CBSE Class 8

These NCERT Solutions for Class 8 Science Chapter 8 Cell – Structure and Functions Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Cell – Structure and Functions NCERT Solutions for Class 8 Science Chapter 8

Class 8 Science Chapter 8 Cell – Structure and Functions Textbook Exercise Questions and Answers

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Question 1.
Indicate whether the following statements are True (T) or False (F).
a. Unicellular organisms have one-celled body. (T/F)
b. Muscle cells are branched. (T/F)
c. The basic living unit of an organism is an organ. (T/F)
d. Amoeba has irregular shape. (T/F)
Answer:
(a) True,
(b) False,
(c) False,
(d) True

Question 2.
Make a sketch of the human nerve cell. What function do nerve cells perform?
Answer:

The function of a nerve cell is to transmit messages to the brain and also from the brain to the receptor organs. Thus, it controls the working of different parts of the body.

Question 3.
Write short notes on the following:
a. Cytoplasm
b. Nucleus of a cell
Answer:
a. Cytoplasm: A jelly-like substance present between the cell membrane and the nucleus is called cytoplasm. Different cell organelles are present in the cytoplasm. Examples of cell organelles are mitochondria, Golgi body, ribosomes, lysosomes, chloroplasts, etc. The cytoplasm acts as a medium for the exchange of materials across the cell organelles.

b. Nucleus of a cell: This is a spherical structure which is present inside the celt usually at the centre of the cell. Nucleus is surrounded by a double membrane called nuclear membrane. A spherical structure called nucleolus is present inside the nucleus. Nucleus contains chromosomes which are thread-like structures carrying genes. These genes are responsible for transferring the characters from parents to their offspring.

Question 4.
Which part of the cell contains organelles?
Answer:
Cytoplasm is the part of the cell that contains various organelles such as mitochondria, ribosomes, Golgi bodies, etc.

Question 5.
Make sketches of animal and plant cells. State three differences between them.
Answer:

Question 6.
State the difference between eukaryotes and prokaryotes.
Answer:

Question 7.
Where are chromosomes found in a cell? State their function.
Answer:
Chromosomes are found inside the nucleus. Chromosomes are responsible for the inheritance of characters from one generation to the next.

Question 8.
‘Cells are the basic structural units of living organisms’. Explain.
Answer:
All organisms are made up of cells. The way a building is made up of bricks, an organism is made up of cells. Many cells group together to make a tissue. Many tissues come together to make an organ which in turn come together to make an organ system. Many organ systems together make an organism. Thus, it is clear that cells are the basic structural units of living organisms.

Question 9.
Explain why chloroplasts are found only in plant cells?
Answer:
Chloroplasts contain a green pigment called chlorophyll. This green pigment is important for photosynthesis in green plants. This chlorophyll pigment traps solar energy and utilises it to manufacture food for the plant. Since animals do not photosynthesise, they do not require chlorophyll. Hence, chloroplasts are found only in plant cells.

Question 10.
Complete the crossword with the help of clues given below.
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.

Answer:
Across
1. Chlorophyll
3. Organelle
6. Protoplasm
8. Genes

Down
1. Chloroplasts
2. Organ
4. Membrane
5. Vacuole
7. Tissue

NCERT Extended Learning Activities and Projects

Question 1.
Visit a laboratory for senior secondary students in your school or in a neighbouring school. Learn about the functioning of a microscope in the laboratory. Also observe how a slide is observed under the microscope.
Hint:
Do it yourself.

Question 2.
Talk to the senior biology teacher in your school or a neighbouring school. Find out if there are diseases which are passed on from parents to the offspring. Find out how these are carried and also if these diseases can be treated. For this you can also visit a doctor.
Hint:
Yes, there are several diseases which are passed on from the parents to their offsprings. These are genetic diseases which are controlled by the chromosomes. Some examples include haemophilia, sickle cell anaemia, Huntington’s disease, etc.

Question 3.
Visit an agriculture extension centre in your area. Find out about genetically modified (GM) crops. Prepare a short speech for your class on this topic.
Hint:
Genetically modified or GM crops refer to the plants whose DNA (or specific genes) has been modified with the help of genetic engineering techniques and are then grown and cultivated. Mutation breeding was the earlier alternative to provide better yields where an organism is exposed to radiations or chemicals to bring permanent changes in the quality of the plant and its yield. The objectives were primarily to prevent the attack of insects and pests, resistance to diseases and changing environmental conditions, enabling a plant to grow in a different soil and climate than the one in which it normally grows. Golden rice is a variety of rice produced through genetic engineering to incorporate vitamin A in it. This improves the nutritional value of rice. Hence, required traits can be incorporated into the GM crops by genetic modifications.

Question 4.
Find out about Bt cotton from an agriculture expert. Prepare a short note on its advantages/disadvantages.
Hint:
But cotton is a genetically modified crop and a pest resistant variety. It contains a gene taken from the bacterium, Bacillus thuringiensis. This gene produces an enzyme which is poisonous to the pests. In this way, But cotton is able to produce this enzyme and kill the invading pests.

Activity 1

Objective: To study the permanent slide of Amoeba.
Materials Required: Slide of Amoeba and a microscope.
Procedure:

• Focus the microscope lens on the slide.
• Study the slide carefully and write your observations.

Observations:

• The body structure of Amoeba is irregular.
• The body of Amoeba has 3 main parts: plasma membrane, cytoplasm and nucleus.
• Amoeba has cytoplasmic projections called pseudopodia which help it in locomotion and feeding.

Cell Structure and Functions

• Tissue: A group of specialised cells which are similar in structure and work together to achieve a specific task is called a tissue.
• Organ: An organ is a group of tissues which together perform a specific function or specialised functions.
• Organ system: An organ system is a group of organs in which each organ performs a different function in order to complete a particular life process. For example, digestive system, respiratory system, etc.

A cell consists of three parts namely cell membrane, cytoplasm and nucleus.
Cell Membrane: Cell membrane is also called plasma membrane. It makes the boundary of a cell. It is composed of proteins and lipids, and is porous. It allows the entry and exit of various materials across it. Cell membrane is semi-permeable in nature which means that it allows only selected materials to pass through it. Following are the functions of a cell membrane:

• Cell membrane separates the contents of the cell from the external environment.
• Cell membrane provides protection to the cell.
• Cell membrane facilitates the exchange of materials between the cell and its external environment.

Cell Wall: Cell wall is an additional covering present next to the cell membrane in plant cells and in bacteria. Cell wall in plants is made up of cellulose. It gives additional strength and protection to the plant cells. It helps the plants to withstand variations in temperature, wind and atmospheric moisture.

Activity 2

Objective: To prepare a slide of onion peel cells and observe it under a microscope.
Materials Required: Onion bulb, glass slide, coverslip, safranin stain, dropper, brush and microscope.
Procedure:

• Cut a slice of onion peel and peel off its skin. Take out the thin membrane present between the two fleshy layers.
• Put this portion of the onion peel in water in the watch glass.
• With the help of a dropper, put one or two drops of safranin stain in the watch glass and mix well with the help of a brush.
• Transfer the peel to a clean and dry glass slide and cut the peel in a proper rectangular shape with the help of a blade or needle.
• With the help of a dropper, put one drop of glycerine on the stained onion peel kept on the slide and gently place a coverslip on it.
• Remove excess of glycerine by using filter paper and observe the slide under the microscope.

Observation: There are a large number of compactly arranged cells. These cells are rectangular in shape. Each cell has a membrane covered with another thick covering called cell wall. They have a jelly-like substance, called the cytoplasm, between the nucleus and the membrane.

Cytoplasm: A jelly-like substance present between the cell membrane and the nucleus is called cytoplasm. It is made up of basic elements found in the form of chemical substances like carbohydrates, proteins and water. Various other components of a cell are suspended in the cytoplasm.

Cell Organelles: Organelles are small structures scattered in the cytoplasm, that work together to carry out various life processes. There are various types of cell organelles that perform different functions. Some of these are as follows:
i. Mitochondria: Mitochondria are small sausage-shaped structures which provide energy in the form of ATP. Therefore, they are known as powerhouse of the cell.

ii. Plastids: Plastids are disc-shaped structures present only in plant cells. They can be of three types-chloroplasts, chromoplasts (provide colour) and leucoplasts (store food). The chloroplast is green in colour due to the presence of green pigment called chlorophyll. It is known as the kitchen of the celt because it helps plant to make food by the process of photosynthesis.

iii. Golgi bodies: These are membranous sac-like structures concerned with the secretion of useful substances such as enzymes and hormones.

iv. Endoplasmic reticulum: The endoplasmic reticulum is a network of membranous tubes that connect the cell membrane with the nuclear membrane and helps to transport the substances in and out of the cell.

v. Ribosome: Ribosomes are tiny structures found either attached to the surface of endoplasmic reticulum or scattered in the cytoplasm. They help in protein synthesis.

vi. Vacuoles: Vacuoles are sac-like structures in the cell. In mature plant cells, they occupy most of the space within the cell and help to store food, water and wastes. In animal cells, vacuoles are smaller and maybe larger in number. They also help in waste removal and digestion.

Nucleus: This is a spherical structure which is present usually at the centre of the cell. Nucleus is surrounded by a double membrane called nuclear membrane. A spherical structure called nucleolus is present inside the nucleus. Nucleus contains genetic material in the form of thread-like structures called chromosomes. These carry genes which are responsible for transferring characters from parents to their offspring. Based on this organisms are divided into two groups:
i. Prokaryotes: When nuclear material is not enclosed by a nuclear membrane, the organism is called a prokaryote. In other words, a true nucleus is absent in prokaryotes. Bacteria and blue-green algae are examples of prokaryotes.

ii. Eukaryotes: When nuclear material is organised and enclosed by a nuclear membrane, the organism is called a eukaryote. In other words, true nucleus is present in eukaryotes. Organisms other than bacteria and blue-green algae are eukaryotes. Animals, plants, fungi, etc., are all eukaryotes.

Activity 3

Objective: To observe the human cheek cells through temporary slide.
Materials Required: Slide, coverslip, toothpick, watch glass, methylene blue stain and microscope.
Procedure:

• Take a clean toothpick and gently scrap the inner side of the cheek.
• Put the epithelial scrapping in a drop of water on a glass slide and spread it evenly.
• Put a drop of methylene blue on the material.
• Put a drop of glycerine on it.
• Put a coverslip on the material taking care that no air bubbles enter.
• Remove extra glycerine with a filter paper.
• Examine the slide under the microscope.

Observation: The human cheek cells are irregular in shape and have a thin cell membrane. A central dense nucleus is also present.

Functions of Nucleus:
i. Nucleus controls the entire functioning of a cell.
ii. Nucleus contains genetic material and controls inheritance of characters, i. e., transfer of characters from one generation to the next generation.

Comparison between Plant Cell and Animal Cell:

Class 8 Science Chapter 8 Cell – Structure and Functions Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define a cell.
Answer:
Cell is the structural and functional unit of life.

Question 2.
Which organism has the smallest cell?
Answer:
Mycoplasma [a bacterium formerly known as pleuro-pneumonia-like organism (PPLO)].

Question 3.
Name the longest plant cell.
Answer:
Fibre of Ramie.

Question 4.
Name the layer outside the plasma membrane of a plant cell.
Answer:
Cell wall.

Question 5.
What are the basic components of a cell?
Answer:
Cell membrane, cytoplasm and nucleus are the basic components of a cell.

Question 6.
What is the common feature of all living organisms?
Answer:
All living organisms are made up of cells which coordinate to perform the various life processes.

Question 7.
A hen’s egg can be seen easily. Is it a cell or a group of cells?
Answer:
The egg of a hen represents a single cell and it is big enough to be seen by an unaided eye.

Question 8.
Name the device that is used to visualise cells in a laboratory.
Answer:
Microscope.

Question 9.
What is the minimum size that can be seen with a microscope?
Answer:
10^-6M.

Question 10.
Define a unicellular organism.
Answer:
An organism which is composed of a single cell is called unicellular organism,
e. g., Amoeba.

Question 11.
Define a multicellular organism.
Answer:
An organism which is composed of more than one cell is called multicellular organism. E.g., humans.

Question 12.
What is tissue?
Answer:
A group of specialised cells which are similar in structure and work together to achieve a particular function is called a tissue.

Question 13.
What is an organ?
Answer:
A group of similar tissues which perform a specific set of functions is called an organ.

Question 14.
What are pseudopodia?
Answer:
Finger-like projections on the surface of the cell of Amoeba are called pseudopodia.

Question 15.
Which is the smallest cell of the human body?
Answer:
Sperm cell.

Question 16.
Which is the longest cell of the human body?
Answer:
Nerve cell.

Question 17.
Define genes.
Answer:
Gene is a unit of inheritance in living organisms which controls the transfer of a hereditary characteristic from parents to offspring.

Question 18.
Define vacuoles.
Answer:
The blank looking structures in the cytoplasm are called vacuoles.

Question 19.
What are plastids?
Answer:
The small coloured bodies in plant cells are called plastids.

Question 20.
Name the green coloured plastids.
Answer:
Chloroplast.

Short Answer Type Questions

Question 1.
Write a short note on plasma membrane.
Answer:
Plasma membrane also called as cell membrane, makes the boundary of a cell. It is composed of proteins and lipids. It is porous and allows various materials to pass through it. Cell membrane is semi-permeable in nature which means that it allows selected materials to pass through it.

Question 2.
What are the functions of the nucleus?
Answer:
Functions of nucleus are as follows:

• Nucleus controls all the functions of a cell.
• It controls the inheritance of characters, i.e., transfer of characters from one generation to the next.

Question 3.
What are the functions of pseudopodia?
Answer:
Functions of pseudopodia are as follows:

• Movement and locomotion
• Capturing food

Question 4.
Differentiate between unicellular and multicellular organisms.
Answer:

Question 5.
What is meant by the term ‘cell division’? Why is cell division necessary?
Answer:
The process by which existing cells divide to form new cells is known as cell division. It is necessary to facilitate the growth of an organism, reproduction and to replace the dead cells.

Question 6.
What is protoplasm?
Answer:
Protoplasm is a fluid viscous substance of the cell and is surrounded by a membrane called plasma membrane. It can be said that protoplasm is cell minus cell membrane. In other words, the nucleus and the cytoplasm together constitute the protoplasm of the cell. It is constituted by different compounds such as water, carbohydrates, proteins, fats, nucleic acid and mineral salts.

Question 7.
Name four elements which form a major part of the protoplasm. What gives living nature to the protoplasm?
Answer:
Ninety-nine percent of protoplasm, by its weight, is made up of four elements, namely, carbon, hydrogen, nitrogen and oxygen. It also contains other elements and compounds such as water, carbohydrates, fats, proteins and mineral acids. Both the elements and the compounds in unique combination provide living nature to the protoplasm.

Question 8.
Describe the discovery of cell.
Answer:
An English researcher named Robert Hooke is credited with the discovery of the cell. In the year 1665, he observed thin slices of cork (a part of the bark of a tree) under a microscope and saw honeycomb structures in it. The slices of cork appeared to be composed of small compartments which were further separated by a wall. Even though, he observed dead cells of the cork, he discovered the building blocks of life and coined the term “cell”. Later, many scientists observed and studied about the cell and its components. They also developed the cell theory.

Question 9.
Why do plants have an extra outer covering called the cell wall?
Answer:
Plant cells are openly exposed to the environment. They need to be protected against the extreme variations of the environment, e.g., change in temperature, moisture, strong winds, etc, The cell wall gives protection from these agents. This becomes more important for plants because unlike animals, they cannot move to escape the harsh climatic conditions.

Question 10.
What is nucleolus?
Answer:
Nucleolus is a small, spherical and dense body present inside the nucleus. It is visible only with a microscope of higher magnification.

Question 11.
What are prokaryotes and eukaryotes?
Answer:
Cells having a well defined nuclear membrane to contain the chromosomes within are called eukaryotic cells and the organisms with such cells are called eukaryotes, e.g., Amoeba. Organisms with cells which do not have well defined nuclear membrane are called prokaryotes, e.g., bacteria.

Question 12.
What are the two types of organisms on the basis of number of cells?
Answer:
On the basis of the number of cells, organisms can be classified as unicellular and multicellular organisms.

• Unicellular organisms are the singled-celled organisms. They are made up of a single cell. Organisms like Amoeba, Paramecium, etc., are single-celled organisms.
• Organisms that consist of more than one cell are known as multicellular organisms, e.g., humans.

Question 13.
Describe the structure of a cell.
Answer:
A typical cell consists of three basic parts: (a) Cell membrane (b) Cytoplasm (c) Nucleus.
a. The cell membrane is also called a plasma membrane. This membrane separates the cells from one another. The plasma membrane is porous and allows the movement of selected substances across it. If forms the boundary of the cell.

b. The cytoplasm is a thick jelly-like fluid inside the cell membrane. It occupies the space between the cell membrane and the nucleus. Various cell organelles are suspended in it.

c. Nucleus is a central, dense and spherical structure present in the cytoplasm. It contains genetic material and controls all the functioning of the cell.

d. Cell wall is an additional rigid covering present in plant cells to provide protection and strength.

Question 14.
Describe the structure of onion peel cells with the help of a diagram.
Answer:
An onion is multicellular (consisting of many cells). As in all plant cells, the cell of an onion peel consists of a cell wall, cell membrane, cytoplasm, nucleus and a large central vacuole. The nucleus is present at the periphery of the cytoplasm. The vacuole is prominent and present at the centre of the cell. It is surrounded by cytoplasm.

Question 15.
Explain the structure of human cheek cells.
Answer:
As in all animal cells, the cells of the inner lining of human cheek do not possess a cell wall. A semi-permeable cell membrane surrounds the cytoplasm. Unlike plant cells, the cytoplasm in an animal cell is denser, granular and occupies a larger space. The vacuole is smaller in size, or absent. The nucleus is present at the centre of the cytoplasm.

Question 16.
Name a cell organelle found only in a plant cell and list its various types.
Answer:
Plastids are the cytoplasmic organelles found only in plant cells. On the basis of pigments, plastids are of three types:

• Leucoplasts (colourless plastids)
• Chloroplasts (green-coloured plastids)
• Chromoplasts (coloured plastids other than green)

Leucoplasts perform the storage of starch and oil drops. Chloroplasts contain chlorophyll and are mainly for photosynthesis. Chromoplasts are responsible for the characteristic colours of flowers and fruits.

Question 17.
Give the functions of the plant cell wall.
Answer:

• The plant cell wall provides definite shape, strength and rigidity to the plant cell.
• It helps in controlling cell expansion.
• It helps in preventing water loss from the cell.
• It is involved in transportation of substances across the cell as well as between two or more cells.
• It acts as a barrier between the cell interior and the outer environment.
• It helps to maintain the shape and size of the cell.
• It protects the plant cells from various disease-causing microbes.
• It provides rigidity to withstand mechanical stress.

Question 18.
Why do plant cells possess large sized vacuoles?
Answer:
Plant cells have distinct vacuoles. They use their vacuoles for transporting and storing nutrients, metabolites and waste products. Plants also accumulate water in their vacuoles when they become larger through turgor pressure driven by inward movement of water.

Question 19.
Shreyansh was taken to the biology lab along with other students where his teacher told the features and differences of plant and animal cells. They were told that plant cells generally have dead cells whereas animal cells have most of the component living in the cell. Shreyansh wants to know if these characters show any advantage.
Do the characters show any advantage to the plants and animals? If yes, what are they?
Answer:
Yes, plants do not have to locomote in search of food as they are autotrophs and so do not need much energy. But the dead cells present in plants provide rigidity to the structure. On the other hand, animals need energy for locomotion and other cellular functions.

Long Answer Type Questions

Question 1.
Explain the position and functions of nucleus in a cell.
Answer:
Nucleus is called the brain of a cell. It is situated within the cytoplasm. It is small in size and spherical in shape. It is filled by a gel-like substance called nucleoplasm. The nucleoplasm is surrounded by a thin nuclear membrane. The nucleoplasm and the cytoplasm together form the protoplasm.

The nucleus controls all the functions of a cell. It directs the functions related to the growth and working of organelles going on in the cell. Nucleus contains the genetic material of the cell in the form of thread-like structures called chromosomes. Chromosomes contain all the genetic information and pass it further to the offspring during reproduction.

Question 2.
What are the functions of the following in a cell-cell membrane, cytoplasm, vacuoles, mitochondria?
Answer:

1. Cell membrane: The cell membrane separates the cell from its surrounding medium and helps in the selective transport of materials into and out of the cell.
2. Cytoplasm: The cytoplasm is a jelly-like substance that makes up most of the inside of a cell. All life functions take place in the cytoplasm. It facilitates the functioning and coordination of various cell organelles suspended in it.
3. Vacuoles: Vacuoles are sac-like structures. They store food, water and wastes and maintain the electrolyte balance of the cell.
4. Mitochondria: Mitochondria are small sausage-shaped structures. They oxidise food to provide energy. They are, therefore, often called the powerhouses of the cell.

Question 3.
With the help of examples, explain the variation in shapes and sizes of the cells.
Answer:
In multicellular organisms, cells have special jobs, according to which they have different shapes and sizes.

• Nerve cells, for example, have fibres that may be more than one metre long. Message passes from one nerve cell to another along these fibres.
• Muscle cells expand and contract. Their long, thin shape helps them do this. The outer layer of skin forms a protective covering over the body. Their flat shape helps them to cover a larger area.
• White blood cells (WBCs) present in the blood can change their shape. This helps them to engulf and destroy the germs.
• Plant cells located on the outer part of the stem give strength to a plant. These cells have thick cell walls for support. Some cells in plants are used to store food. These cells are larger than other cells.

Question 4.
What are the main points of the cell theory of life?
Answer:
The main points of the cell theory of life are as follows:

• The cell is the basic structural and functional unit of life. All organisms are composed of cells.
• All celts arise from pre-existing cells. Each cell contains genetic material that is passed on to the next generation during this process.
• All the basic chemical and physiological functions, e.g., repair, growth, movement, immunity, communication and digestion, are carried out inside the cells,
• The activities of cells depend on the activities of sub-cellular structures within the cell. These sub-cellular structures include organelles, plasma membrane and nucleus.

Picture-Based Questions

Question 1.
Draw a labelled diagram of (a) Amoeba (b) Paramecium. Name the locomotory organs in both of them.
Answer:


Locomotory organs: Amoeba moves with the help of pseudopodia while Paramecium moves through cilia.

Question 2.
Draw a labelled diagram of a prokaryotic cell.
Answer:

Question 3.
Draw a well-labelled sketch of the plant cell.
Answer:

These NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Conservation of Plants and Animals NCERT Solutions for Class 8 Science Chapter 7

Class 8 Science Chapter 7 Conservation of Plants and Animals Textbook Exercise Questions and Answers

Page 86-87

Question 1.
Fill in the blanks:
a. A place where animals are protected in their natural habitat is called ……………….
b. Species found only in a particular area is known as ……………….
c. Migratory birds fly to far away places because of ………………. changes.
Answer:
a. wildlife sanctuary,
b. endemic species,
c. climate

Question 2.
Differentiate between the following:
a. Wildlife sanctuary and biosphere reserve
Answer:

b. Zoo and wildlife sanctuary
Answer:

c. Endangered and extinct species
Answer:

d. Flora and Fauna
Answer:

Question 3.
Discuss the effects of deforestation on the following:
a. Wild animals
b. Environment
c. Villages (Rural areas)
d. Cities (Urban areas)
e. Earth
f. The next generation
Answer:
a. Wild Animals: When forests are cut, the natural habitat of animals is destroyed. Without their natural habitat, the animals are left with no place to live and breed. As a result of this, many animals are on the verge of their extinction.

b. Environment: Environment is adversely affected by deforestation as ecological balance is disturbed. Carbon dioxide is not absorbed by plants and it gets accumulated in the atmosphere leading to global warming. It increases the temperature of the earth and disturbs the water cycle.

c. Villages (Rural areas): The villagers depend on forests for their basic needs. They are closely related to forests. Due to deforestation, various wild animals run to nearby villages and cause danger to people living there. Also, villagers will not get sufficient fruits, fuel and wood due to deforestation.

d. Cities (Urban areas): People in urban areas may not get sufficient products, for which raw materials come from forests. Reduction in farm output results in rise of price of food items.

e. Earth: The whole earth is full of various ecosystems which together make up the biosphere. Deforestation disturbs the balance in the biosphere. It disturbs climatic patterns, natural habitats, etc.

f. The next generation: The next generation will be the biggest sufferer because of deforestation. They will find drastic seasonal and climatic changes. Natural calamities like droughts and floods will become more frequent. Air quality will be very poor. They will also find very little vegetation and wildlife on the earth.

Question 4.
What will happen if:
a. we go on cutting trees?
b. the habitat of an animal is disturbed?
c. the top layer of soil is exposed?
Answer:
a. Mindless cutting of trees will result in deforestation. This will result in various kinds of damage to the environment. It will result in global warming, increased cases of floods and droughts. It will also result in many wild animals getting wiped off the earth.

b. If the habitat of an animal is disturbed, it will suffer from shortage of food and space to live. Many wild animals would enter human settlements in search of food. Instances of clash between humans and wild animals will be on rise. A complete destruction to habitat may even lead to the extinction of that animal species.

c. The soil will become deficient in humus and important nutrients. In the long run, the soil will become infertile. The whole area would become a desert in due course of time.

Question 5.
Answer in brief:
a. Why should we conserve biodiversity?
b. Protected forests are also not completely safe for wild animals. Why?
c. Some tribals depend on the jungle. How?
d. What are the causes and consequences of deforestation?
e. What is Red Data Book?
f. What do you understand by the term migration?
Answer:
a. A healthy biodiversity is necessary to maintain a healthy ecosystem. This is important for our survival. Hence, we need to conserve biodiversity.

b. In spite of various laws, it is difficult to completely stop the poaching of wild animals. Moreover, environmental damage in the surrounding areas can harm even the protected forests. Hence, it can be said that protected forests are also not completely safe for wild animals.

c. Tribal people have been living in or around the jungle since ages. They use most of the forest produce for their day-to-day needs. For example, they use firewood as kitchen fuel, bamboo to make houses and many useful items, medicinal plants to treat diseases, etc. They also take various items from forests to sell them into the market in order to earn some money. Thus, tribals depend on the jungles in a significant way.

d. Following are the causes of deforestation:

• Procuring land for cultivation.
• Building houses and factories.
• Making furniture and using wood as fuel.
• Clearing land for making roads, railway lines, dams, etc.
• Grazing cattle.

Following are the consequences of deforestation:

• Reduced forest cover increases the level of carbon dioxide in the atmosphere. This results in global warming.
• Reduces groundwater level.
• Reduces rainfall.
• Reduces soil fertility.
• Can result in severe droughts or in excess floods.
• May also lead to desertification.

e. The International Union for Conservation of Nature and Natural Resources (IUCN) first came with the Red Data Book. It is a sourcebook which keeps record of all the endangered plants and animals. Each country publishes its own version of Red Data Book from time to time.

f. The long distance movement undertaken by animals to escape the harsh climatic conditions of an area is called migration. Many birds and animals migrate long distances during unfavourable seasons. Human beings also migrate in search of livelihood. Siberian crane migrates from Siberia to India during winters to escape the harsh conditions in Siberia and to get comfortable climatic conditions and food in India.

Question 6.
In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.
Answer:
The question arises a conflict between development and conservation. But when we keep in mind the need for sustainable development, it becomes necessary to strike a balance between development and conservation. If we keep on clearing forests in the name of economic development, a time will come when there will be no forests left. That will be disastrous for the environment. All efforts should be done to prevent clearing of forests as much as possible. If clearing of trees is at all necessary, suitable measures should be taken for reforestation at alternate locations to compensate for the loss of trees.

Question 7.
How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you.
Answer:
We can help in maintaining the green wealth of our locality in the following ways:

• By practising horticulture and floriculture.
• By practising afforestation.
• Motivating people so that they do not destroy their green surroundings for more space and other requirements.
• Bringing awareness among citizens regarding the importance of conserving our environment.

Question 8.
Explain how deforestation leads to reduced rainfall.
Answer:
Plants help in bringing rain by recycling moisture from the soil. Plants absorb water from the deeper layers of soil. This water is released into the atmosphere as water vapour by the process of transpiration. This helps in bringing rain. In the absence of forests, there will be no significant transpiration, hence cloud formation will be affected. This will ultimately reduce rainfall.

Question 9.
Find out about national parks in your state. Identify and show their location on the outline map of India.
Answer:
Do it yourself.

Question 10.
Why should paper be saved? Prepare a list of ways by which you can save paper.
Answer:
Paper is made from wood pulp. This means that trees need to be cut down to make paper. However, paper can be recycled many times. Recycling of paper helps in saving trees. This will save our environment. We can save paper in the following ways:

• Use every page of notebook for writing and never leave a page blank.
• Use pencil wherever possible so that your writing can be erased to make the pages reusable.
• Do not waste paper by making paper planes.
• Use old envelopes and pamphlets for doing rough calculations during solving mathematics problems.
• Reuse old envelopes and packets.
• Use notebooks of recycled paper for rough works.

Question 11.
Complete the world puzzle.
Down
1. Species on the verge of extinction.
2. A book carrying information about endangered species.
5. Consequence of deforestation.
Across
1. Species which have vanished.
3. Species found only in a particular habitat.
4. Variety of plants, animals and microorganisms found in an area.

Answer:
Down:
1. Endangered
2. Red Data Book
5. Deserts

Across
1. Extinct
3. Endemic
4. Biodiversity

NCERT Extended Learning Activities and Projects

Question 1.
Plant at least five different plants in your locality during this academic year and ensure their maintenance till they grow.
Hint:
Do it yourself.

Question 2.
Promise yourself that this year you will gift at least 5 plants to your friends and relatives on their achievements, or on occasions like birthdays. Ask your friends to take proper care of these plants and encourage them to gift plants to their friends on such occasions. At the end of the year count the plants that have been gifted through this chain.
Hint:
Do it yourself.

Question 3.
Is it justified to prevent tribals from staying in the core area of the forest? Discuss the matter in your class and note down the points for and against the motion in your notebook.
Hint:
Points in favour of the motion: Yes, it is justified since the core area of a forest (biosphere reserve) is a legally protected ecosystem. Endangered plants and animals are kept here. In case tribals are permitted to stay in the core area of the biosphere reserve, they would disturb the animals and plants residing there, thus defeating the main purpose of creating a biosphere reserve.

Points against the motion: It is not justified because forests are the livelihood and habitat of tribals. They have very deep knowledge of forests and also care to preserve them. They depend on forests for their daily needs, livelihood, culture, etc.

Question 4.
Study the biodiversity of a park nearby. Prepare a detailed report with photographs and sketches of the flora and fauna.
Hint:
Do it yourself.

Question 5.
Make a list of the new information you have gathered from this chapter. Which information did you find the most interesting and why?
Hint:
In this chapter, we found the information about the following topics:
Deforestation and its consequences, conservation of forests and wildlife, flora and fauna and their habitats, protected areas (wildlife sanctuaries, national parks and biosphere reserves), endemic species, endangered species, extinct species, Red Data Book, migration of animals and birds, recycling of paper, and reforestation.

Recycling of paper and ways of saving paper may be regarded as the most interesting information as by saving papers we can contribute towards saving the environment to some extent.

Question 6.
Make a list of various uses of papers. Observe currency notes carefully. Do you find any difference between a currency paper and paper of your notebook? Find out where currency paper is made.
Hint:
Paper is used in making notebooks, envelopes, newspapers, tissue papers, currency notes, for recording any statement and so on. Normal paper is made from the cellulose found in trees while currency paper is made from cotton and linen fibers. Currency paper is thin compared to normal paper. India imports currency paper from NATO (North Altlantic Treaty Organisation) countries but mostly from United Kingdom (NATO member) and Germany (NATO member).

Question 7.
Karnataka Government had launched ‘Project Elephant’ to save Asian elephants in the state. Find out about this and other such campaigns launched to protect threatened species.
Hint:
Project Elephant (PE), a centrally sponsored scheme, was launched by the Karnataka Government in February 1992 to provide financial and technical support to major elephant bearing states in the country for the protection of elephants, their habitats and corridors. It also seeks to address the issues of human-elephant conflict and welfare of domesticated elephants. The Project is being implemented in 13 States/Union territories, namely, Andhra Pradesh, Arunachal Pradesh, Assam, Jharkhand, Karnataka, Kerala, Meghalaya, Nagaland, Orissa, Tamil Nadu, Uttarakhand, Uttar Pradesh and West Bengal.

Other such campaigns launched to protect the threatened species are Gir Lion Project, Crocodile Breeding Project, Rhino Conservation, Snow Leopard Project, Chiru Conservation, etc.

Activity 1

Objective: To understand the factors disturbing biodiversity.
Procedure: List the factors disturbing the biodiversity of your area. Some of these factors and human activities may disturb the biodiversity unknowingly. List these human activities and discuss how these can be checked.

Observation: There are various factors which can disturb the biodiversity of an area. The big factors are cutting of trees and using the forest land for construction and industrialisation. Excessive rains or droughts also affect the biodiversity of an area. Certain human activities which give rise to polluting end products also disturb the biodiversity. When plants and animals do not get clean environment, they die.

The government conserves our forests and wildlife: The government lays down rules, regulations and policies to protect our forests and wildlife. Besides, it also earmarks rich flora and fauna habitats as protected areas where the activities like cutting down trees, grazing cattle, hunting, plantation and cultivation, poaching (illegal killing or capturing wild animals), etc., are prohibited.

Biosphere Reserve: A biosphere reserve is an area which aims to conserve the biodiversity of the area as well as its culture. It may contain other protected areas within it. For example, Pachmarhi Biosphere Reserve has a national park called the Satpura National Park and two wildlife sanctuaries called the Bori Wildlife Sanctuary and the Pachmarhi Wildlife Sanctuary.

Wildlife Sanctuary: A sanctuary is an area where animals are protected from any disturbance to them or their habitat. In a wildlife sanctuary, poaching (killing) or capturing animals is strictly prohibited. Sanctuaries have given protection to many endangered species like black buck, white eyed buck, elephant, golden cat, pink-headed duck, gharial, marsh crocodile, python, rhinoceros, etc.

Some of the well known sanctuaries in India are Gir wildlife sanctuary in Gujarat, Periyar wildlife sanctuary in Rajasthan, etc.

National Park: A national park is an area which is reserved for wildlife, and where wildlife can freely use the habitat and natural resources. Satpura National Park is the first reserve forest of India. Rock shelters and rock paintings are also preserved along with the flora and fauna. Some famous national parks of India include Corbett National Park in Uttarakhand, Ranthambhor National Park in Rajasthan, etc.

Activity 2

Objective: To learn about the functions of a zoo.
Procedure: Visit a nearby zoo and observe the conditions provided to the animals. Compare these conditions with their natural habitat.
Observation: The conditions provided to animals in a zoo are artificial. Animals are kept in cages for the purpose of public view. Animals live happily and comfortably only in their natural habitat.

Project Tiger: Project Tiger was launched in 1973 to protect and conserve tigers in India. This project was aimed at protecting the Bengal Tigers. Project Tiger has been successful in improving the population of tigers in India. At present, there are more than 2,000 tigers in India.

Red Data Book: The International Union for Conservation of Nature and Natural Resources (IUCN) first came with the Red Data Book. It is a sourcebook which keeps record of all the endangered plants and animals.

Migration: Long distance movement by animals to escape harsh climatic conditions is called migration. Many birds and animals migrate long distances during unfavourable seasons. For example, Siberian crane migrates from Siberia to India during winters to escape harsh conditions in Siberia and to get comfortable conditions and food in India.

Recycling of Paper: Paper can be recycled many times. As paper is made from wood pulp, recycling of paper helps in saving trees.
Reforestation: Planting trees to recover forests is called reforestation. Reforestation can take place naturally as welt as by human intervention.

Forest (Conservation) Act: The Forest (Conservation) Act of Indian parliament came into effect in 1980. This Act aimed at the preservation and conservation of natural forests and meeting the basic needs of the people who live in or near the forests.

Class 8 Science Chapter 7 Conservation of Plants and Animals Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is desertification?
Answer:
Conversion of fertile land into desert is called desertification.

Question 2.
What is biosphere?
Answer:
The part of earth where all living organisms are present is called biosphere. It is a narrow zone between atmosphere, lithosphere and hydrosphere.

Question 3.
What are the natural causes of deforestation?
Answer:
The natural causes of deforestation are forest fires and severe drought.

Question 4.
What is biodiversity?
Answer:
The variety of living organisms (plants, animals and microbes) existing on the earth comprises biodiversity.

Question 5.
What do you understand by fauna?
Answer:
The animal species found in a particular area are collectively termed as fauna.

Question 6.
What is the function of a biosphere reserve?
Answer:
A biosphere reserve helps to maintain the biodiversity and culture of an area. One biosphere reserve may contain other protected areas in it.

Question 7.
What is a species?
Answer:
A group of population capable of interbreeding is called a species.

Question 8.
What is an extinct species?
Answer:
A species which no longer exists on earth is called an extinct species, e.g., species of dinosaurs, dodo, etc.

Question 9.
What is the role of a national park?
Answer:
A national park helps in preserving the flora, fauna, landscape and historical objects of an area.

Question 10.
What do you mean by endangered species?
Answer:
Species which are under the threat of extinction are called endangered species, for example, elephants, lions, wild buffalo, etc.

Question 11.
Name the first reserved forest of India.
Answer:
Satpura National Park.

Question 12.
What are migratory birds? Give examples.
Answer:
The birds who cover long distances to reach another land for finding suitable climatic conditions are known as migratory birds, e.g., bar-headed goose, Arctic tern, Siberian crane.

Question 13.
Define seed banks.
Answer:
A seed bank is a place where seeds are preserved under controlled conditions to maintain their viability or germinating capacity and to preserve the genetic diversity.

Short Answer Type Questions

Question 1.
What do you understand by endemic species? Give some examples.
Answer:
Species which are found exclusively in a particular area are called endemic species. Sal and wild mango are the flora endemic to Pachmarhi Biosphere Reserve. Bison, Indian giant squirrel and flying squirrel are the fauna endemic to this region.

Question 2.
State some factors which can lead to the extinction of an endemic species.
Answer:
Following can lead to the extinction of an endemic species:

• Destruction of natural habitat.
• Introduction of an exotic species.
• Increase in population and urbanisation.
• Agriculture

Question 3.
What are the features of the members of a species?
Answer:
Members of a species show the following features:

• They look similar.
• They can interbreed.
• They can produce fertile offsprings among themselves only.

Question 4.
How does deforestation reduce rainfall on one hand and lead to floods on the other hand?
Answer:
The cloud formation for rain depends on the water lost by the plants through transpiration and evaporation. So, when the number of trees is reduced, there is a decrease in humidity. Hence, proper cloud formation does not occur and the rainfall is reduced. On the other hand, water holding capacity of the soil is adversely affected by the reduction in the number of trees.

The soil structure also changes. The roots of trees grown deep into the land, firmly bind the soil particles together and help in absorption and underground seepage of flowing water. However, in the absence of trees, soil loses its water holding capacity. In this situation, when there is a heavy rainfall, the water does not seep down into the ground and is not absorbed by the soil. Hence, it flows out and leads to floods.

Question 5.
What is Project Tiger?
Answer:
The Project Tiger was launched on 1st April, 1973 by our government to protect the tigers of our country. Its main objective was to ensure the maintenance of a viable population of tigers in our country.

Question 6.
What are the two reasons for migration of animals?
Answer:
Following are the reasons for migration of animals:

• Unfavourable climatic conditions
• Lack of food
• Breeding and spawning
• Habitat destruction

Question 7.
How does deforestation cause global warming?
Answer:
We know that plants take up carbon dioxide and release oxygen during photosynthesis. This helps in maintaining the balance of carbon dioxide and oxygen in the atmosphere. Deforestation results in loss of green cover on the earth. Due to less number of plants, the level of carbon dioxide increases in the atmosphere. Carbon dioxide traps solar energy and thus leads to an overall increase in the global temperature. Thus, deforestation causes global warming.

Question 8.
Write any three functions of a biosphere reserve.
Answer:
Functions of a biosphere reserve are as follows:

• It helps to maintain the biodiversity of that area.
• It helps to maintain the culture of that area.
• It prevents the commercial exploitation of the area.

Question 9.
Why was IUCN established?
Answer:
International Union for the Conservation of Nature and Natural Resources was established by the United Nations to promote the conservation of wildlife and habitats as part of the national policies of member states.

Question 10.
How does deforestation lead to a decrease in the water holding capacity of the soil?
Answer:
Forests drop organic matter on the surface of soil. This organic matter holds a lot of water. Also, the trees have roots which go deep into the soil. When these roots die and rot, they leave holes in the soil and channels for water to get into the soil. Hence, due to deforestation all these phenomena stop and soil loses its water holding capacity.

Question 11.
Why is it important to conserve forests?
Answer:
It is important to conserve forests because forests:

• maintain the level of CO₂ in the atmosphere.
• bind the top layer of soil, thereby increasing its fertility.
• help in absorbing rainwater and thus, preventing floods.
• maintain the water cycle.
• serve as a natural habitat for various species.

Question 12.
Can a forest regenerate naturally in a short period of time?
Answer:
Reforestation (i.e., regeneration of a forest) can take place naturally by leaving the deforested area undisturbed for some time. During this period, the forest re-establishes itself without the interference of human beings by the natural growth of trees. This process, however, takes many years.

Question 13.
Why are wildlife sanctuaries important for the conservation of plants and animals?
Answer:
In a wildlife sanctuary, killing and capturing of wild animals is strictly prohibited. Any human activity which disturbs the wild animals and plants or their habitat is not allowed. So, in these areas, animals live in their natural environment protected from any human interference. This is why, sanctuaries are important for conservation of plants and animals.

Question 14.
Why are endemic organisms in greater danger of becoming extinct?
Answer:
Endemic organisms are confined to a limited geographical area. They cannot adapt or live outside their natural habitat. This means that any disturbance to their habitat will adversely affect them. Thus, they are in a greater danger of becoming extinct.

Question 15.
What is the unique feature of the biodiversity found in Pachmarhi Biosphere Reserve?
Answer:
The biodiversity found in Pachmarhi Biosphere Reserve is similar to that of the upper Himalayan peaks and to that belonging to the lower Western Ghats. Thus, it is unique.

Question 16.
How does recycling of certain things help in saving our environment?
Answer:
Plastic, paper, glass and metals can be recycled easily. Their recycling helps in saving our environment in the following ways:

• Recycling helps in saving land as we do not require large land area for dumping waste.
• Recycling prevents the faster depletion of natural resources.
• Recycling prevents pollution of land, water and air.

Question 17.
What are the causes of extinction of wildlife?
Answer:
Causes of extinction of wildlife are:

• Indiscriminate cutting of forests which destroys their habitat.
• Large scale mining and raising of huge buildings and dams which disturbs the natural habitat of many animals.
• Natural calamities such as droughts, floods and forest fires have made many of the rare species extinct.
• Indiscriminate hunting and poaching of animals.

Question 18.
What type of animals are much more in danger of becoming extinct?
Answer:
The smaller animals are much more in danger of becoming extinct than the bigger animals. People kill snakes, frogs, lizards, bats and owls ruthlessly without realising their importance in the ecosystem. They might be small in size but their role in the ecosystem cannot be ignored. They form a part of food chains and food webs.

Long Answer Type Questions

Question 1.
Explain the different types of protected areas.
Answer:
Different types of protected areas are as follows:
a. Sanctuary: An area where animals are protected from any disturbance to them or their habitat is called a sanctuary. Poaching (killing) or capturing an animal is strictly prohibited in a wildlife sanctuary. Some examples of wildlife sanctuaries are Bharatpur bird sanctuary, Gir sanctuary, etc. Some examples of threatened species which are protected in wildlife sanctuaries in India are: black buck, white eyed buck, elephant, golden cat, pink headed duck, gharial, marsh crocodile, python, rhinoceros, etc.

b. National Park: Areas reserved for wildlife where they can freely use the habitat and natural resources are called national parks. Satpura National Park is the first reserve forest of India. Other examples are Corbett national park, Kariranga national park, etc.

c. Biosphere Reserve: Large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in that area are called biosphere reserves, e.g., Pachmarhi Biosphere Reserve, Nitgiri Biosphere Reserve, etc.

Question 2.
Discuss five methods of forest conservation.
Answer:
Five methods of forest conservation can be:

1. Planned harvesting, i.e., cutting only some of the trees in an area. The uncut trees prevent soil erosion and produce seeds so that new trees can grow.
2. Afforestation (or Reforestation), which means renewing a forest by planting seedlings or small trees of the same species as found in that forest.
3. Protection from forest fires by spraying fire extinguishing solutions from aircrafts.
4. Protection from insects and pests by using insecticides and fungicides and removing infected trees.
5. Protection from overgrazing to protect the growing plants by providing pastures which can be obtained as by products from agricultural fields.

Question 3.
Discuss the steps necessary for wildlife conservation?
Answer:
The steps necessary for wildlife conservation are:
a. Habitat preservation: Preserving the habitat of wildlife helps in their conservation. Preventing deforestation is an important method of habitat preservation. Afforestation provides shelter and food for the wildlife.

b. Hunting regulations: Government regulations related to hunting and their effective implementation is very important for wildlife conservation. The hunting of endangered species is completely banned.

c. Biosphere Reserves, Wildlife Sanctuaries and National Parks: To effectively implement the methods of conserving forests and wildlife, the government has set aside permanent protected areas for conservation of biodiversity in that area. These include biosphere reserves, national parks and wildlife sanctuaries. They provide protection and suitable living conditions for wild animals and plants. Living organisms can breed and multiply in these areas.

Question 4.
Differentiate between afforestation and deforestation.
Answer:
The difference between afforestation and deforestation is summarised below:

Picture-Based Questions

Question 1.
Draw a labelled diagram depicting the greenhouse effect.
Answer:

Question 2.
Identify the following map and name two wildlife sanctuaries and a national park.

Answer:
The map shows the Pachmarhi biosphere reserve.
Two sanctuaries are: Bori and Pachmarhi. The national park is Satpura national park.

These NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Combustion and Flame NCERT Solutions for Class 8 Science Chapter 6

Class 8 Science Chapter 6 Combustion and Flame Textbook Exercise Questions and Answers

Page – 75

Question 1.
List conditions under which combustion can take place.
Answer:
Following are the conditions under which combustion can take place:

• The presence of fuel is necessary.
• The presence of air or oxygen.
• Heat should be supplied to raise the temperature of the fuel beyond its ignition temperature.

Question 2.
Fill in the blanks:
a. Burning of wood and coal causes …………… of air.
b. A liquid fuel, used in homes is ……………
c. Fuel must be heated to its …………… before it starts burning.
d. Fire produced by oil cannot be controlled by ……………
Answer:
(a) pollution,
(b) kerosene,
(c) ignition temperature,
(d) water

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:
The use of diesel and petrol as fuels in automobiles is a major cause of air pollution today. During combustion, these fuels release a large amount of unburnt carbon particles which are highly poisonous and harmful for living beings and the environment. These fine particles are dangerous pollutants causing respiratory diseases, such as asthma. Incomplete combustion of these fuels gives off carbon monoxide gas. It is a very poisonous gas.

Combustion of most fuels releases carbon dioxide in the environment. Increased emission of carbon dioxide in the air is one of the major causes for global warming. The use of diesel and petrol as fuels in automobiles is being replaced by CNG (Compressed Natural Gas), because CNG produces the harmful products in very small amounts. CNG is a cleaner fuel. It has high fuel efficiency. Hence use of CNG in automobiles has reduced pollution in our cities to a noticeable extent.

Question 4.
Compare LPG and wood as fuels.
Answer:
Wood has traditionally been used as a kitchen fuel and is still predominantly being used in rural areas. Burning of wood releases many air pollutants which can result in respiratory problems. Moreover, incomplete oxidation during burning of wood releases carbon monoxide gas which is a poisonous gas. LPG is a much better fuel because it bums without giving any smoke. It produces lesser amount of air pollutants. Complete oxidation during burning of LPG does not lead to the formation of carbon monoxide gas.

Question 5.
Give reasons:
a. Water is not used to control fires involving electrical equipment.
b. LPG is a better domestic fuel than wood.
c. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer:
a. Pure water is a bad conductor of electricity but normal water contains many salts and hence is a good conductor of electricity. Trying to put off fires involving electrical equipment with water can result in electric shock. Due to this, water is not used to control fires involving electrical equipment.

b. LPG is a better domestic fuel than wood because of several reasons. Unlike wood, LPG bums without smoke. This makes the life of the cook more comfortable and they do not have to worry about blackening of pots and pans. Moreover, use of LPG as domestic fuel also rules out the chances of getting respiratory disorders which may happen when someone uses wood as kitchen fuel. Storage and transportation of LPG is easier as compared to that of wood,

c. The ignition temperature of paper is lower as compared to that of aluminium. When paper is wrapped around an aluminium pipe, the ignition temperature increases. That is why paper itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Question 6.
Make a labelled diagram of a candle flame.
Answer:

Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer:
Kilojoule per kilogram (kJ/kg).

Question 8.
Explain how CO₂ is able to control fires.
Answer:
Carbon dioxide is heavier than oxygen. Due to this, carbon dioxide forms a blanket around the burning material and makes a barrier between the burning material and oxygen. As oxygen supply is cut off, it helps in extinguishing the fire.

Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer:
Green leaves contain moisture and as a result, the ignition temperature of green leaves is much higher than that of dry leaves. Due to this, it is difficult to bum a heap of green leaves but dry leaves catch fire easily.

Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer:
The outermost zone of a flame is the hottest zone. Due to this, goldsmith uses the outermost zone of a flame for melting gold and silver.

Question 11.
In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer:
Total mass of the fuel = 4.5 kg
Heat produced by burning the given mass of fuel = 180,000 kJ.
We know that calorific value of fuel = \(\frac{\text { Heat produced in } \mathrm{kJ}}{\text { Total mass burnt }}\)
= \(\frac{180,000 \mathrm{~kJ}}{4.5 \mathrm{~kg}}\) = 40,000 kJ/kg
Hence, the calorific value of the given fuel is 40,000 kJ/kg.

Question 12.
Can the process of rusting be called combustion? Discuss.
Answer:
Although the process of rusting also involves oxidation, yet it cannot be termed as combustion. The reason for this is that combustion is defined as a process in which oxidation is accompanied by heat, and heat is not produced during rusting.

Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer:
Since Abida has kept the beaker in the luminous zone of the flame, the beaker will take more time to get heated as this zone is moderately hot. On the other hand, Ramesh has kept the beaker in the non-luminous zone of the flame so his beaker will be heated in shorter time as this is the hottest zone of the flame.

NCERT Learning Activities and Projects

Question 1.
Survey the availability of various fuels in your locality. Find out their cost per kg and prepare a tabular chart showing how many kJ of various fuels you can get for every rupee.
Hint:
Do it yourself.

Question 2.
Find out the number, type and location of fire extinguishers available in your school, nearby shops and factories. Write a brief report about the preparedness of these establishments to fight fire.
Hint:
Basically there are two types of fire extinguishers. They are carbon dioxide fire extinguishers and water fire extinguisher.
Others may include water and foam, dry chemical, wet chemical, clean agent, water mist, etc.
Carbon dioxide fire extinguisher is used when there are fires caused by oil, petrol
or by any electric appliance. Water fire extinguisher is used to fight fires caused by wood or paper.

Question 3.
Survey 100 houses in your area. Find the percentage of households using LPG, kerosene, wood and cattle dung as fuel.
Hint:
Do it yourself.

Question 4.
Talk to people who use LPG at home. Find out what precautions they take in using LPG.
Hint:
The following precautions must be taken while using LPG cylinders:
a. Before igniting the gas, we should make sure that there is no foul smell of the leaking gas. If there is a foul smell of gas, then the doors and windows should be opened at once to allow the gas to escape. The gas cylinder, rubber tubing and gas stove should then be properly checked to detect the cause of gas leakage. Preferably, a mechanic should be called to fix the defect. The gas should be used only after the defect has been rectified. Never use a leaking gas cylinder.
b. We should not use any open flames, like a kerosene stove or an electric heater, near the gas cylinder.
c. The rubber pipe connecting the gas cylinder to the gas stove should be checked regularly for any wear and tear.
d. The gas cylinder should be handled with care to avoid any damage to the cylinder valve.
e. The cylinder valve should be closed when the gas stove is not in use.
f. While lighting the gas stove, we should first open the cylinder (regulator) valve and then turn the knob of the gas stove.

Question 5.
Make a model of a fire extinguisher. Place a short candle and a slightly taller candle in a small dish filled with baking soda. Place the dish at the bottom of a large bowl. Light both the candles. Then pour vinegar into the dish of baking soda. Take care. Do not pour vinegar on the candles. Observe the foaming reaction. What happens to the candles? Why? In what order?

Hint:
When vinegar is combined with baking soda, the two react and produce carbon dioxide gas. The carbon dioxide gas is heavier than the surrounding air so it sinks into the bottom of the bowl. As the reaction continues, more and more carbon dioxide gas is produced which begins to fill up the bowl slowly. When the level of carbon dioxide has risen to the level of the flame, the flame will be extinguished due to lack of oxygen.

Activity 1

Objective: To show that air is necessary for combustion.
Materials Required: A lighted candle, glass chimney, a glass plate and wooden blocks.
Procedure:

• Fix a lighted candle on a table.
• Put a glass chimney over the candle and rest it on a few wooden blocks in such a way that air can enter the chimney. Observe what happens to the flame.
• Now remove the blocks and let the chimney rest on the table. Again observe the flame.
• Finally, put a glass plate over the chimney. Watch the flame again.

Observations:

• When we bum the candle under the chimney rested on the wooden blocks, the candle bums in the presence of air.
• When we remove the blocks, the candle flame flickers and produces smoke in the absence of air.
• When we put a glass plate on it, in the complete absence of air, the flame finally goes off.

Conclusion: In the absence of air, the candle flame goes off. Hence, air is necessary for combustion.

Activity 2

Objective: To show that a substance does not catch fire at a temperature below its ignition temperature.
Materials Required: Candle (two), sheet of paper and water.
Procedure:

• Take a sheet of paper and make two paper cups (100 mL) by folding the paper.
• Place some water into one of the cups so as to fill it up to one-third of its height.
• Hold both the cups separately over burning candle and observe.

Observations:

• When the cup is empty, it catches fire easily.
• When the cup having water in it is heated, it does not catch fire and the water becomes hot and starts boiling.

Conclusion: When we heat a paper bowl containing water, the water present in it absorbs the heat coming from the burning source and thus prevents the paper from reaching its ignition point. Hence, it does not bum.

Contents of a Modern Matchstick:
Matchsticks are in use since ages. Modem matchsticks are made up of a mixture of antimony trisulphide and potassium chlorate with some glue and starch applied on the head of the matchstick. The mbbing surface has powdered glass and some red phosphorus. On striking match stick against the rough surface, red phosphorus gets converted into white phosphorus and it reacts with potassium chlorate to ignite antimony trisulphate, due to which combustion takes place.

Types of Combustion: There are following three types of combustion:
i. Rapid Combustion: When combustion happens at a faster rate, it is called rapid combustion. Petrol and gas show rapid combustion. For example, bring a burning matchstick or gas lighter near a gas stove in the kitchen. Turn on the l knob of the gas stove. We find that the gas burns rapidly and produces heat and light.

ii. Spontaneous Combustion: When combustion starts on its own without an apparent cause, it is called spontaneous combustion. For example, many disastrous fires in coal mines result due to this kind of combustion. The heat rays coming from the sun or a lightning strike might be responsible for this kind of combustion.

iii. Explosion: When combustion reaction is so sudden that it releases a large amount of heat, light and sound, it is called explosion. Fire-crackers explode because of this type of combustion.

Flame: Flame is the visible and gaseous part of fire. When vapour of a substance undergoes combustion, it results in the formation of flame. Only those substances which vapourise on burning produce flame. If a substance does not get vapourised, it does not produce flame on burning.

Three Distinct Zones of a Candle Flame

1. Outer Zone: This zone is blue in colour. It is the hottest part of the flame because compLete combustion takes place in this zone.
2. Middle Zone: This zone is yellow or orange in colour. This zone is moderately hot because partial combustion takes place in this zone. It contains unburnt carbon particles.
3. Inner Zone: This zone is dark in colour. This is the least hot part of the flame because no combustion takes place in this zone. Here, we can find the unburnt wax vapours of a candle.

Activity 3

Objective: To show the presence of unburnt carbon particles in the middle zone of the candle flame.
Materials Required: A wax candle, matchbox, glass slide and a pair of tongs.
Procedure:

• Light the candle and allow the flame to become steady.
• Introduce a clean glass slide into the luminous region of the flame holding it with a pair of tongs.
• Remove the glass slide after 3-4 minutes.

Observation: A circular grey ring forms on the glass.
Conclusion: The circular dark ring is formed on the slide by the deposition of unburnt carbon particles present in the luminous (middle) zone of the candle flame.

Fuel: The substance that undergoes combustion is called a fuel. The fuel can be in the form of solid, liquid or gas.

• Liquid Fuels: Petroleum, crude oil, diesel, kerosene oil, etc.
• Solid Fuels: Firewood, charcoal, coal, dung cake, tallow (animal fat), straw and other agricultural wastes, paraffin wax, camphor, etc.
• Gaseous Fuels: Most commonly used gas, i.e. LPG (Liquid Petroleum Gas) which we use as cooking gas at home and CNG (Compressed Natural Gas).

Characteristics of a Good Fuel:

• It should be easy to store and transport.
• It should bum smoothly without emitting harmful gases.
• It should not produce any smoke.
• It should have moderate ignition temperature.
• It should have high calorific value.

There is probably no fuel that could be considered as an ideal fuel.

Calorific Value: Calorific value gives the measure of fuel efficiency. The amount of heat energy produced on combustion of 1 kg of a fuel is called the calorific value of that fuel. It is expressed as kilo Joule per kg (kJ/kg).

Fire Extinguishers: A substance which disrupts the contact between air and fire so that the fire goes off is called a fire extinguisher. Some common fire extinguishers are as follows:
i. Water: Water is the most commonly used fire extinguisher. It helps in bringing down the ignition temperature of the fuel. When water is poured over a burning material, steam is formed due to heat. The layer of steam cuts off air supply. Thus, water helps in putting off fire.

Drawbacks of Water: Water cannot be used for fires due to oil because oil is lighter than water. When water is poured over fire, oil comes on top and continues to bum. Also, water should not be used for electric fires. We know that water is a good conductor of electricity because it contains many salts. This increases the risk of electric shock for the firefighters.

ii. Blanket: If fire is at a small scale, a blanket can be very useful in controlling the fire. When the burning object is covered with blanket, the oxygen supply is cut off from the fuel. This helps in putting off fire.

iii. Carbon Dioxide: This is the best fire extinguisher. Carbon dioxide creates a blanket over fire and cuts off air supply because it is heavier than air. Carbon dioxide expands quickly and brings down the temperature of the fuel. This helps in putting off fire.

For extinguishing fire, carbon dioxide can be supplied in any of the following ways:

• Carbon dioxide is stored in pressurised cylinders and can be released through a nozzle.
• In soda-acid fire extinguishers, carbon dioxide is evolved because of reaction between soda and acid.
• Baking soda (sodium bicarbonate) or potassium bicarbonate powder is sprayed on the burning substance. The powder releases carbon dioxide because of heat.

Harms of Burning Fossil Fuels:

• Burning of carbon fuels (wood, coal and petroleum) results in the release of unburnt carbon particles in air. These particles cause respiratory disease, like asthma.
• Incomplete combustion of carbon fuels releases carbon monoxide. It is a poisonous gas, even in low concentrations. Hence, coal should not be burnt in a closed room.
• Burning of most fuels results in release of carbon dioxide in the atmosphere. Higher level of carbon dioxide in the atmosphere causes global warming.
• Burning of coal, and diesel results in the release of sulphur dioxide in the air. Burning of petrol produces oxides of nitrogen. Oxides of sulphur and nitrogen mix with rainwater to cause acid rain. Acid rain is harmful for living beings, buildings, crops and for monuments.

Class 8 Science Chapter 6 Combustion and Flame Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define combustion.
Answer:
Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Question 2.
Give examples of some fuels used in our day to day life.
Answer:
Cow dung, coal, wood, petrol, charcoal, compressed natural gas (CNG), etc.

Question 3.
What are the products of combustion?
Answer:
Carbon dioxide, water vapour, heat and light.

Question 4.
What is a combustible substance?
Answer:
A substance which can undergo combustion is called a combustible substance, e.g., wood, paper, kerosene, etc.

Question 5.
What is a non-combustible substance?
Answer:
A substance which cannot undergo combustion is called a non-combustible substance, e.g., stone, soil, etc.

Question 6.
What is an inflammable substance?
Answer:
A substance which has very low ignition temperature and can easily catch fire is called an inflammable substance, e.g. petrol, alcohol.

Question 7.
What is a flame?
Answer:
Flame is the visible and gaseous part of the fire formed by the burning of vapours of fuel.

Question 8.
What is the colour of LPG flame?
Answer:
The colour of LPG flame is blue.

Question 9.
What is a fire extinguisher?
Answer:
The substance which is used for putting off fire is called fire extinguisher.

Question 10.
Give an example of rapid combustion.
Answer:
When we bring a burning matchstick or gas lighter near a gas stove and turn on the knob of stove, the gas bums rapidly and produces heat and tight. This is an example of rapid combustion.

Question 11.
What is the principle to extinguish fire?
Answer:
Fire can be controlled by removing one or more of the essential requirements-air, fuel or heat.

Question 12.
Name two different types of fire extinguishers.
Answer:

• Soda-acid fire extinguisher (contains baking soda and acid),
• Fire extinguisher cylinders having CO₂ stored at high pressure.

Question 13.
Give examples of the substances which give off flame on burning.
Answer:
Kerosene and molten wax.

Question 14.
Give two properties of an ideal fuel.
Answer:
High calorific value and low cost.

Question 15.
Which chemicals give rise to acid rain?
Answer:
Sulphur dioxide and nitrogen oxides.

Short Answer Type Questions

Question 1.
Differentiate between rapid and spontaneous combustion.
Answer:

Question 2.
Why does kerosene oil catch fire faster than wood?
Answer:
This is because the specific heat capacity of the wood is more than that of the kerosene oil. Hence, the wood takes time to bum but burns for a longer period than the kerosene oil.

Question 3.
How many types of combustion are there? Explain them.
Answer:
There are three types of combustion:

1. Rapid Combustion: When combustion happens at a faster rate, it is called rapid combustion. Petrol and gas show rapid combustion.
2. Spontaneous Combustion: When combustion starts on its own, without any apparent cause, it is called spontaneous combustion. For example, coal dust in coal mines can start burning on its own. Forest fires are spontaneous in most of the cases.
3. Explosion: When combustion reaction is so sudden that it releases a large amount of heat, light and sound, it is called an explosion. Firecrackers explode because of this type of combustion.

Question 4.
Explain the different zones of a candle flame with the help of a labelled diagram.
Answer:
A flame has three zones:

• Outermost zone is blue in colour and is the hottest part of the flame. This is also the zone where complete combustion takes place.
• Middle zone is yellow in colour and is moderately hot. In this zone, partial combustion takes place.
• Innermost zone is black in colour and least hot. Here, we can find the unburnt wax vapours of a candle.

Question 5.
State the characteristics of a good fuel.
Answer:
The characteristics of a good fuel are:

• It is readily available.
• It is cheap.
• It bums easily in air.
• It bums at a moderate rate.
• It produces a large amount of heat.
• It does not leave behind any undesirable substance.
• It is easy to store and transport.

Question 6.
List the different methods by which a fire can be extinguished.
Answer:
A fire can be extinguished by one or more of the following methods:

1. Removing the combustible substance.
2. Cooling the substance to bring its temperature below its ignition temperature using water.
3. Cutting off the supply of air or using fire extinguishers.

Question 7.
What is calorific value of a fuel? Why is hydrogen not used as a fuel though it has the highest calorific value?
Answer:
Calorific value: The amount of heat energy produced on complete combustion of one kilogram of a fuel is called the calorific value of that fuel. Hydrogen is not used as a fuel because it has very low ignition temperature and is highly explosive in nature.

Question 8.
How are fuels classified on the basis of their physical state? Give two examples of each.
Answer:
Fuels can be classified on the basis of their physical state as follows:

• Solid fuels: Some solid fuels are wood, coal, cattle-dung cakes, etc.
• Liquid fuels: Some of the liquid fuels are kerosene, LPG, petrol, diesel, etc.
• Gaseous fuels: Some of the gaseous fuels are CNG, coal gas, water gas, producer gas, biogas, etc.

Question 9.
Why are we advised never to sleep in a closed room with burning coal fire in it?
Answer:
In the presence of less amount of oxygen, the carbon monoxide gas is produced by incomplete combustion of coal. It is a poisonous gas and can kill the person sleeping in a closed room. Hence, we are advised not to sleep in a closed room with burning coal fire in it.

Question 10.
Why is the colour of outer zone of a candle flame blue while middle zone is yellow in colour?
Answer:
Outermost Zone: It is blue coloured because complete combustion takes place in this part due to sufficient amount of oxygen. It is the hottest part of the flame.

Middle Zone: The colour of the middle zone is yellow because incomplete combustion takes place in this part due to lack of oxygen. It is comparatively less hot than the outer part of the flame.

Question 11.
What do you mean by global warming? Write its effects.
Answer:
The increase in temperature of the atmosphere of the earth is called global warming. This causes melting of polar ice caps which leads to a rise in the sea level, causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged underwater. Global warming is the result of increase of carbon dioxide concentration in the atmosphere, mostly due to combustion of fuels.

Question 12.
What can we do to cut off the air supply of a burning substance?
Answer:
To put off the air supply of a burning substance, we can cover the surface of the burning substance with sand, foam or a thick cloth like a blanket. Fire extinguishers form a layer of foam or carbon dioxide on the surface of the burning substance.

Question 13.
Why does a matchstick start burning when it is rubbed on the side of the matchbox?
Answer:
The head of the matchstick is made from antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus. When the matchstick is struck against the rubbing surface, some of the red phosphorus is converted into white phosphorus. This immediately reacts with potassium chlorate in the matchstick head to produce enough heat to ignite antimony trisulphide and starts the combustion of matchstick.

Question 14.
Why should we not use water to control oil fires? What should be done to control fire due to oils?
Answer:
Water should never be used for extinguishing oil fires. This is because oil is lighter than water. Oil forms a thin layer over the surface of water and flows with the water, thereby spreading the fire to larger areas. In such a case, sand or soil should be used. They cut off the supply of air and the fire is put off.

Question 15.
How does fire brigade work to extinguish fire?
Answer:
Firemen throw water with pressure on the fire. Water helps in cooling down of the combustible material so that its temperature is brought below its ignition temperature and the fire is controlled. Apart from this, combustible material is surrounded by water vapour which helps in cutting off the air supply and finally the fire is extinguished.

Long Answer Type Questions

Question 1.
Describe the working of soda-acid fire extinguisher.
Answer:
Soda-acid fire extinguisher: This fire extinguisher is a metallic cylinder which contains sodium bicarbonate (NaHCO₃) solution. At the bottom of the cylinder, the concentrated sulphuric acid (H₂SO₄) is placed in a thin sealed glass tube. Fixed wire gauze surrounds this tube.

Below the tube, a plunger is placed with its sharp end touching the thin glass tube. On the top of the cylinder, there is a nozzle which is sealed with wax. When the plunger hits against the floor, its sharp end breaks the thin glass tube and the acid inside it reacts with sodium bicarbonate to produce carbon dioxide. CO₂ forces the wax seal open and rushes out of the nozzle to put out the fire in the direction where the nozzle is pointed.

Question 2.
Discuss the impact of burning fuels on air quality.
Answer:
The main impacts due to burning of fuels are as follows:
a. Burning of carbon-containing fuels releases ash and fine particles of unburnt carbon in the air. These fine particles, called SPM (suspended particulate matter) are dangerous pollutants.

b. Combustion of fuels adds carbon dioxide to the environment. A percentage increase in carbon dioxide in the air leads to the greenhouse effect which can cause global warming. This can result in melting of the polar ice caps and rise in sea levels, leading to floods in low-lying areas.

c. Carbon monoxide produced when fuels containing carbon bum in insufficient supply of air, is a very poisonous gas and can cause death if breathed in.

d. Coal contains sulphur, which produces sulphur dioxide on burning. Besides being a poisonous gas, it dissolves in rain to form sulphuric acid. This gives rise to acid rain, which is very harmful for soil, crops, buildings, etc.

e. The oxides of nitrogen given off from the exhausts of engines of vehicles are poisonous gases. Many vehicles now use catalytic converters to convert these oxides to harmless gases.

f. Lead compounds are released in exhausts of vehicles. They are poisonous. Increasing use of unleaded petrol is expected to reduce lead pollution.

Question 3.
Name the fire extinguisher used for fires involving electrical equipment and inflammable materials. What are its advantages as a fire extinguisher?
Answer:
The most commonly used fire extinguisher is water. It works when wood and paper are on fire. But if electrical equipment is on fire, water may conduct electricity and may harm those trying to douse the fire. Also, water is not suitable for fires involving oil and petrol, since water is heavier than oil, so it sinks below the oil and oil keeps burning on the top. Hence, if electrical equipment and inflammable materials are on fire, carbon dioxide is the best extinguisher. Since it is heavier than oxygen, it covers the burning material so that the contact between fuel and oxygen is cut off and the fire is controlled. It also brings down the temperature of the fuel. For this purpose, carbon dioxide is stored at high pressure, as a liquid, in cylinders.

Question 4.
Describe the history of matchstick.
Answer:
The history of matchstick is very old. More than 5000 years ago, small pieces of pinewood dipped in sulphur were used as matches in ancient Egypt. The modem safety match was developed only 200 years ago. A mixture of antimony trisulphide, potassium chlorate and white phosphorus with some glue and starch was applied on the head of match made of wood. When struck against a rough surface, white phosphorus got ignited due to heat of friction. This started the combustion of matchstick. However, white phosphorus proved to be dangerous to health, both for the workers involved in manufacturing and the users. These days red phosphorus is used in place of white phosphorus.

Picture Based Questions

Question 1.
Observe the given figure and answer the following questions.

a. Name the article shown above.
b. Name two different varieties in which this article is available.
c. How does it work?
Answer:
a. Fire extinguisher.
b. Carbon dioxide and soda-acid type fire extinguisher.
c. It works by cutting off air supply to the burning fuel.

Question 2.
a. Draw a diagram to show the flame of:
(i) Candle (ii) Kerosene lamp and (iii) Bunsen burner.
b. Write the colour of these flames.
Answer:
a.

Flame of (a) candle (b) kerosene lamp, and (c) Bunsen burner
b. The colour of the flame of kerosene lamp and candle is yellow. The colour of the flame of Bunsen burner is blue.

These NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Coal and Petroleum NCERT Solutions for Class 8 Science Chapter 5

Class 8 Science Chapter 5 Coal and Petroleum Textbook Exercise Questions and Answers

Page 62-63

Question 1.
What are the advantages of using CNG and LPG as fuels?
Answer:
Following are the advantages of using CNG and LPG as fuels:

• CNG and LPG are the cleanest of all the fossil fuels. They do not leave behind any residue on burning.
• Compressed Natural Gas (CNG) and LPG are less polluting and non-corrosive which can be used for burning.
• Calorific value of these fuels is very high. Hence they are used for cooking purposes.

Question 2.
Name the petroleum product used for surfacing of roads.
Answer:
These days bitumen, a petroleum product, is used for surfacing the roads in place of coal tar.

Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer:
Millions of years ago, dense forests and animals got buried under the soil due to natural processes like floods, earthquakes and thunderstorms. When they got buried deep in the soil, they were exposed to very high pressure and temperature. Under these conditions, these slowly got converted into coal. This process of formation of coal is called carbonisation.

Question 4.
Fill in the blanks:
a. Fossil fuels are ………………, ……………… and ………………
b. Process of separation of different constituents from petroleum is called ………………,
c. The least polluting fuel for vehicle is ………………,
Answer:
a. coal, petroleum, natural gas,
b. refining,
c. CNG

Question 5.
Tick True/False against the following statements:
a. Fossil fuels can be made in the laboratory. (T/F)
b. CNG is more polluting fuel than petrol. (T/F)
c. Coke is almost pure form of carbon. (T/F)
d. Coal tar is a mixture of various substances. (T/F)
e. Kerosene is not a fossil fuel. (T/F)
Answer:
(a) False
(b) False
(c) True
(d) True
(e) False

Question 6.
Explain why fossil fuels are exhaustible natural resources.
Answer:
Fossil fuels require millions of years to form from the dead vegetation and animals that got buried deep inside the earth. They require high temperature and pressure for their formation, which cannot be provided in the laboratory. Thus, fossils are limited. Therefore, the use of fossil fuels at this rate will lead to their exhaustion. Since, the time taken for the formation of fossil fuels is much higher than the human life span, they are considered as exhaustible natural resources.

Question 7.
Describe characteristics and uses of coke.
Answer:
Coke is a type of coal. It is a tough, porous and black substance. It is almost pure form of carbon. Coke is much cleaner than coal and provides more energy on burning. It is used in the manufacture of steel and in the extraction of many minerals.

Question 8.
Explain the process of formation of petroleum.
Answer:
Petroleum is a dark, oily and thick liquid. It is a mixture of various fractions. Petroleum was formed by the decomposition of the remains of tiny plants and animals under the sea. It is believed that millions of years ago, the tiny plants and animals which lived in the sea, died. Their dead bodies sank to the bottom of sea and were soon covered with mud and sand. Due to high pressure, heat, action of bacteria and in the absence of air. the dead remains of tiny plants and animals were slowly converted into petroleum. The petroleum thus formed got trapped between the two layers of impervious rock, forming an oil deposit.

The more volatile component of petroleum formed a gaseous cover over petroleum. Such a gaseous mixture covering the crude oil is known as natural gas.

Question 9.
The following table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.

Answer:
Scale: Along X-axis: 1 unit = 1 year
Along Y-axis: 1 unit = 1%

NCERT Extended Learning Activities and Projects

Question 1.
Get an outline map of India. Mark the places in the map where coal, petroleum and natural gas are found. Show the places where petroleum refineries are situated.
Hint:
Do it yourself.

Question 2.
Choose any five families of your neighbourhood. Enquire whether their energy consumption (coal, gas, electricity, petrol, kerosene) has increased or decreased in the last five years. Enquire also about the measures they adopt to conserve energy.
Hint:
Do it yourself.

Question 3.
Find out the location of major thermal power plants in India. What could be the reasons for their being located at those places?
Hint:
Do it yourself.

Activity 1

Objective: To classify the resources as natural or man-made.
Materials Required: Pen and paper.
Procedure:

• Observe your surroundings and make a list of various materials used by us in daily life.
• Classify these materials as natural or man-made in a table as shown below.

Observation:

Conclusion: Natural resources like air, water, sunlight, etc., are present in nature while man-made resources like building, roads, plastics, etc., are synthesised by humans.

Fossil Fuels: Dead remains of organisms (plants or animals) which are more than 10,000 years old are called fossils. The fuels which are formed by the decomposition of fossils over millions of years are called fossil fuels, e.g., coal and petroleum.

Coal: Coal is a hard, black, combustible mineral that consists mainly of carbon. It is formed by the deeply buried remains of vegetation under high pressure and high temperature over millions of years. Since coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.

Uses of Coal: Coal bums in air to produce heat and carbon dioxide. Coal is used as a fuel because it provides large amount of heat energy.
C + O₂ → CO₂

• Coal was used as a fuel in steam engines.
• Most of the thermal power plants still use coal as a fuel.
• Coal is still being used as a kitchen fuel in some households, dhabas and restaurants.
• Many useful products, like coke, coal-tar and coal gas, are made by processing coal.

Destructive distillation: When any substance is heated in the absence of air to form a number of different products, the process is known as destructive distillation. The products which are obtained by the process of destructive distillation of coal are coke, coal tar and coal gas.
i. Coke: Coke is an almost pure form of carbon, is tough, porous and black. Coke is used in the manufacture of steel and extraction of many metals.
ii. Coal Tar: It is a black thick liquid with an unpleasant smell. Coal tar is a mixture of about 200 substances. It is used as a raw material for making various items like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls, etc. It is used for making the surface of roads. Bitumen (a petroleum product) has almost replaced coal tar for making road surfaces.
iii. Coal Gas: Coal gas is produced during the processing of coke from coal. Coal gas is used as a fuel in many industries which are situated near coal mines.

Petroleum: Petroleum is a dark oily liquid and has a foul smell. It contains many constituents like petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.

Formation of Petroleum: Petroleum was formed from the organisms living in the seas. When these organisms died, their bodies got settled at the bottom of the sea and eventually, layers of sand and clay got deposited over them. After millions of years in the absence of air, the high temperature and high pressure converted them into petroleum and natural gas. Today, we drill down through layers of sand, silt and rock to reach the rock formation that contains oil and natural gas deposits.

Refining of Petroleum: It is the process of separating the various constituents of petroleum and is carried out in a petroleum refinery. The various constituents of petroleum and their uses are as follows:
Various Constituents of Petroleum and their Uses

Natural Gas: Natural gas is considered important as this fossil fuel can easily be transported through pipes. It is stored as CNG (compressed natural gas) which is used for several purposes and is also used as a starting material for manufacturing many chemicals and fertilisers. Natural gas does not cause pollution and has a high calorific value.

Limitations of Natural Resources: Fossil fuels like coal, petroleum, etc., need millions of years to get transformed from dead bodies into fuels. But currently, their demands are so high that after a few hundred years there will be a scarcity of these resources. In addition, too much of air pollution is caused when these fuels are burnt. These fuels are also responsible for the problems associated with the global warming. Hence, it is very important to use these fuels wisely.

Some of the PCRA (Petroleum Conservation Research Association) recommendations for the conservation of petrol and diesel are as follows:

• Drive at constant and moderate speed as far as possible.
• Switch off the engine at traffic lights or at a places where you have to wait.
• Ensure correct tyre pressure.
• Ensure regular maintenance of the vehicle.

Class 8 Science Chapter 5 Coal and Petroleum Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is a natural resource?
Answer:
A resource which is obtained from nature is called a natural resource.

Question 2.
What do you mean by inexhaustible natural resources?
Answer:
The resources which are available in huge quantity and cannot be exhausted by human activities are called inexhaustible natural resources, e.g. sunlight, air, water, etc.

Question 3.
What is an exhaustible natural resource?
Answer:
A resource which is available in limited quantity and can be exhausted by human activities is called exhaustible natural resource, e.g., coal, petroleum, natural gas, etc.

Question 4.
Name the substance obtained from coal tar which is used to repel moths
and insects.
Answer:
Naphthalene ball.

Question 5.
Where was the first oil well drilled?
Answer:
The first oil well was drilled at Pennsylvania, USA, in 1859.

Question 6.
Name two fractions of petroleum which are used as fuel.
Answer:
Petrol and diesel.

Question 7.
Where and when was the first oil well drilled in India?
Answer:
In 1867, at Digboi in Assam.

Question 8.
What is diesel?
Answer:
Diesel is a fuel which is used in heavy vehicles, like buses and trucks. It is obtained after refining of petroleum.

Question 9.
Can we use all our natural resources forever?
Answer:
No, we cannot use all our natural resources forever because these are going to exhaust one day.

Question 10.
Define petrochemicals.
Answer:
The useful substances formed from natural gas and petroleum are called petrochemicals.

Question 11.
Why is coke not used as a fuel?
Answer:
It is more valuable when used in the extraction of metals, hence not used as a fuel.

Question 12.
How do we obtain coke from coal?
Answer:
By the process of destructive distillation.

Question 13.
Which fuel is promoted as a pollution-free fuel?
Answer:
CNG.

Question 14.
Why is natural gas a convenient fuel?
Answer:
It is because natural gas can be supplied through pipes in homes and is less polluting.

Question 15.
Write some places of India where oil is found.
Answer:
Assam, Gujarat, Bombay High and river basins of Godawari and Krishna.

Question 16.
Which constituents are separated from petroleum during refining?
Answer:
Petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.

Short Answer Type Questions

Question 1.
What is coal? Write its uses.
Answer:
Coal is a black stone like substance. It is formed by the dead remains of the living organisms.
Uses of coal:

• Coal was used as a fuel in steam engines.
• Most of the thermal power plants still use coal as a fuel.
• Coal is still being used as kitchen fuel in some households, dhabas and restaurants.
• Many useful products like coke, coal tar and coal gas are made by processing coal.

Question 2.
What is coal-tar? How is it useful to us?
Answer:
The black liquid obtained during destructive distillation of coal is known as coal tar. It is thick, viscous and has unpleasant smell. It is a mixture of hundreds of substances. It is used as a raw material for making various items like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls, etc. It is used for making the surface of roads.

Question 3.
What happens after the petroleum is taken out of the oil well?
Answer:
Crude oil needs to be processed to obtain useful products. After extraction from oil wells, petroleum is sent to oil refineries. Petroleum is subjected to fractional distillation in the oil refinery where various constituents of petroleum are separated through this process.

Question 4.
Define refining of petroleum.
Answer:
Petroleum is a dark oily liquid. It has an unpleasant odour. It is a mixture of various constituents such as petrol, diesel, etc., and the process of separating these constituents from crude oil is called refining.

Question 5.
Why should we use certain resources, like coal and petroleum, judiciously?
Answer:
As we know that coal and petroleum are fossil fuels. The dead organisms take millions of year to get converted into these fuels. On the other hand, the known reserves of these fuels will last only a few hundred years. Apart from this, these products are not environment-friendly as burning of these fuels is a major cause of air pollution and their use is also linked to global warming. Hence, we should use these resources only when absolutely required.

Question 6.
What can be the potential effect of petroleum products on the environment?
Answer:
The effect of petroleum products on environment is as follows:

• While transporting petroleum and its products, there might be oil spillage.
• The process of refining petroleum generates various products that can lead to air and water pollution.
• Drilling of petroleum may result into serious disturbances in the aquatic life.
• Any leakage in the tanks in which petroleum is stored may lead to pollution and deterioration of groundwater.

Question 7.
Differentiate between renewable and non-renewable sources of energy with one example of each.
Answer:

Question 8.
Write down the consequence of excessive usage and mining of coal and petroleum.
Answer:
Excessive usage and mining of coal and petroleum may:

• lead to energy crisis.
• result in creation of a large hollow space underneath which may cause minor earthquakes or landslides.
• lead to the greenhouse effect, acid rain and many health-related problems.

Question 9.
Why is coke considered a better fuel than coal? Give three reasons.
Answer:
Coal and coke are both fuels. But, coke is considered to be a better fuel than coal because of the following reasons:

• Coke has higher calorific value than coal. So, coke produces more heat than the same mass of coal.
• Coke does not produce smoke on burning. So, there is lesser air pollution when coke is burnt as compared to the burning of coal.

Question 10.
What is the basis of the process of fractional distillation of petroleum?
Answer:
The different components of petroleum have distinctly different boiling points. These components get separated in the fractional distillation tower when their boiling point is reached. The component having the maximum boiling point is at the bottom while the component having the minimum boiling point is at the top.

Long Answer Type Questions

Question 1.
Describe some ways to conserve fossil fuels.
Answer:
Economic and controlled consumption of fossil fuels can help conserving our natural resources. Following ways and measures can conserve our fossil fuels:

• Vehicles should be driven at constant and moderate speed.
• Engines should be switched off at traffic lights or other temporary halts.
• Proper and regular maintenance of vehicles should be done.
• Vehicle pooling can reduce the number of vehicles plying on the road, thereby decreasing fuel consumption.
• At home, gas stoves should be cleaned properly and burners should not be left burning unnecessarily.
• Pressure cookers should be preferred to pans. If pans are being used, they should be properly covered and their bottoms should not have deposits of burnt oil.
• Small pans and burners should be used and pulses, etc., should be soaked in water before cooking them.

Question 2.
What are the different constituents of petroleum and their uses?
Answer:
Following are the various constituents of petroleum oil obtained during fractional distillation in oil refineries:

• LPG or petroleum gas is used as a fuel for home and industry.
• Petrol is used as a motor fuel, aviation fuel and a solvent for dry cleaning.
• Kerosene is used as a fuel for stoves and lamps and also in jet aircrafts.
• Diesel is used as a fuel for heavy motor vehicles and electric generators.
• Lubricating oil is used for many lubricating purposes.
• Paraffin wax is used in ointments, candles and Vaseline.
• Bitumen is used in paints and also to surface the roads.
• Petrochemicals are used in the manufacture of detergents, polyester, nylon fibres, polythene and other man-made plastics.

Question 3.
Discuss the advantages of using compressed natural gas.
Answer:
Advantages of CNG:

• CNG is a very important fossil fuel because it is easy to transport through pipes.
• CNG is also used for power generation and now used as a fuel for vehicles because it is less polluting.
• It is a cleaner fuel.
• Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs is eliminated.
• CNG-powered vehicles have low maintenance cost when compared with other fossil fuel-powered vehicles.
• CNG fuel systems are sealed which prevents any spill or evaporation losses.
• CNG mixes easily and evenly in air being a gaseous fuel.
• CNG is less likely to auto-ignite on hot surfaces, since it has a high auto-ignition temperature and a narrow range of flammability. Thus it is less polluting and more efficient.

Question 4.
What is destructive distillation of coal? Describe the constituents obtained from this process.
Answer:
The process in which a solid material (usually coal or wood) is heated at high temperature in absence of air to make coke, coal tar and charcoal is called. It is called ‘destructive’ because the chemical composition of the end product is significantly different from that of the input material.

a. Coke: Coke is almost pure form of carbon, is tough, porous and black. Coke is used in manufacture of steel and extraction of many metals.

b. Coal tar: It is a black thick liquid with an unpleasant smelt. Coal tar is a mixture of about 200 substances. It is used as a raw material for making various items, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls, etc. It is used for making the surface of roads. Bitumen (a petroleum product) has almost replaced coal tar for making road surface.

c. Coal gas: Coal gas is produced during the processing of coke from coal. Coal gas is used as a fuel in many industries which are situated near coal mines.

Question 5.
Prakash worked in an MNC which is 20 km away from the society. He had a CNG vehicle and he displayed a notice in his society informing the people that if anybody is interested to pool a car, feel free to contact him for the same.
a. What is the fuel used in CNG vehicle and how it is better than petrol?
b. Mention two harmful effects/ disadvantages of petrol as a fuel.
Answer:
a. The compressed natural gas and methane is the fuel used in CNG vehicles. Compressed natural gas is a clean-burning fuel. It is actually the cleanest of all fossil fuels. Since natural gas is composed mainly of methane, burning it produces carbon dioxide and water vapour. These are the same compounds we exhale when we breathe. On the other hand, petroleum produces higher carbon emissions, nitrogen oxides and sulphur dioxide. Burning fuel oil also produces ash particulates that worsen pollution,

b. Two harmful effects of petrol are:

• It can lead to environmental pollution.
• It can be harmful to health.

Picture-Based Questions

Question 1.
Observe the given figure and answer the following questions:

a. Name the substance shown.
b. Name the process by which it is obtained.
c. Give any three uses of this substance.
Answer:
a. Coal tar.
b. Destructive distillation.
c. It is used in the manufacturing of dyes, drugs, paints, naphthalene balls, etc.

Question 2.
Draw a line diagram to show the position of layers of natural gas, petroleum and water deposits.
Answer:

These NCERT Solutions for Class 8 Science Chapter 4 Materials: Metals and Non-Metals Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Materials: Metals and Non-Metals NCERT Solutions for Class 8 Science Chapter 4

Class 8 Science Chapter 4 Materials: Metals and Non-Metals Textbook Exercise Questions and Answers

Page 53-55

Question 1.
Which of the following can be beaten into thin sheets?
a. Zinc
b. Phosphorus
c. Sulphur
d. Oxygen
Answer:
a. Zinc

Question 2.
Which of the following statements is correct?
a. All metals are ductile.
b. All non-metals are ductile.
c. Generally, metals are ductile.
d. Some non-metals are ductile.
Answer:
c. Generally, metals are ductile.

Question 3.
Fill in the blanks:
a. Phosphorus is a very …………….. non-metal.
b. Metals are …………….. conductors of heat and ……………..
c. Iron is …………….. reactive than copper.
d. Metals react with acids to produce …………….. gas.
Answer:
a. reactive,
b. good, electricity,
c. more,
d. hydrogen

Question 4.
Mark ‘T’ if the statement is true and ‘F’ if it is false.
a. Generally, non-metals react with acids. ( )
b. Sodium is a very reactive metal. ( )
c. Copper displaces zinc from zinc sulphate solution. ( )
d. Coal can be drawn into wires. ( )
Answer:
a. False
b. True
c. False
d. False

Question 5.
Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties.

Answer:

Question 6.
Give reasons for the following:
a. Aluminium foils are used to wrap food items.
b. Immersion rods for heating liquids are made up of metallic substances.
c. Copper cannot displace zinc from its salt solution.
d. Sodium and potassium are stored in kerosene.
Answer:
a. Aluminium reacts with air to make a coating of aluminium oxide on it. This layer prevents aluminium from further reactions with any substance. Due to this, aluminium foils are used to wrap food items because it does not react with food.

b. Metals are good conductors of heat and have a high melting point. Immersion rods need to heat up quickly and should not melt at high temperatures. Hence, immersion rods for heating liquids are made up of metallic substances.

c. Copper is less reactive than zinc. Hence, copper cannot displace zinc from its salt solution.

d. Sodium and potassium are highly reactive and react vigorously with water even at room temperature. The reaction is highly exothermic and the reaction mixture instantly catches fire. Sodium and potassium are stored in kerosene to prevent this reaction and to prevent accidental fire.

Question 7.
Can you store lemon pickle in an aluminium utensil? Explain.
Answer:
No, it is not possible to store lemon pickle in an aluminium utensil because lemon pickle is acidic and can react with aluminium (metal) liberating hydrogen gas. This may spoil the pickle.

Question 8.
Match the substances given in Column A with their uses given in Column B.

Answer:
(i) → d,
(ii) → e,
(iii) → c,
(iv) → f,
(v) → b,
(vi) → a

Question 9.
What happens when
a. Dilute sulphuric acid is poured on a copper plate?
b. Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.
Answer:
a. Copper does not react with dilute sulphuric acid. So, no reaction takes place when dilute sulphuric acid is poured on a copper plate. However, when concentrated sulphuric acid is poured on copper plate, hydrogen gas evolves along with the formation of blue coloured copper sulphate crystals.
Cu + H₂SO₄ (conc.) → CuSO₄ + H₂O
Copper + Dilute sulphuric acid → No reaction

b. When iron nails are placed in copper sulphate solution, the blue colour of copper sulphate solution is replaced by a light green colour. This happens because, iron being more reactive than copper, displaces copper from copper sulphate and makes iron sulphate solution.
Copper sulphate (blue) + Iron → Iron sulphate (light green) + Copper
Fe + CuSO₄ → FeSO₄ + Cu

Question 10.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
a. How will she find the nature of the gas?
b. Write down word equations of all the reactions taking place in this process.
Answer:
a. Saloni should bring a wet blue litmus paper near the evolved gas. If litmus paper turns to red, it indicates that the evolved gas is acidic in nature.

b. Carbon (in charcoal) reacts with oxygen to produce carbon dioxide gas.
C + O₂ → CO₂
Carbon dioxide reacts with water to form carbonic acid.
CO₂ + H₂O → H₂CO₃ (acidic)

Question 11.
One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?
Answer:
Jewellers use aqua regia to clean the jewellery. Gold is an inert metal which does not react with acids. But aqua regia is a mixture of hydrochloric acid and nitric acid in 3 : 1 ratio. It is so potent that it even dissolves gold and silver. Some of the gold is thus lost during the cleaning of jewellery. This explains the weight loss in jewellery.

NCERT Extended Learning Activities and Projects

Question 1.
Prepare Index Cards for any four metals and four non-metals. The card should have information like name of metal/non-metal; its physical properties, chemical properties and its uses.
Hint:
Uses of Metals

• Iron metal is used for making cooking vessels, water boilers, stoves, tools, wires, nails, bolts, electromagnets, etc.
• Aluminium is a very light metal so it is used in making the aircraft bodies,
• Copper is most widely used for making electric wires and all things related to electricity because it is a good conductor of electricity,
• Silver is widely used for making jewellery.

Uses of Non-metals

• Phosphorous is used in matchbox industry and in fertilisers,
• Iodine is used as an antiseptic,
• Oxygen is essential for all living beings.
• Sulphur is used for making firecrackers, gun powder and sulphuric acid.

Question 2.
Visit a blacksmith and observe how metals are moulded.
Hint:
Do it yourself.

Question 3.
Suggest an experiment to compare the conductivity of electricity by iron, copper, aluminium and zinc. Perform the experiment and prepare a short report on the results.
Hint:
Let us make a simple circuit by connecting one end of the torch bulb to a cell and another end of torch bulb to an aluminium metal strip or wire and back to the cell (as shown in figure).
Repeat the same activity with different metal strips like iron, copper and zinc.

In the case of copper, we will observe that the bulb glows the fastest and more brightly than others, while in case of iron, the bulb glows the slowest and less brightly than the others.
Hence, the sequential order of their decreasing electrical conductivity is: copper → aluminium → zinc → iron.

Question 4.
Find out the locations of the deposits of iron, aluminium and zinc in India. Mark these in an outline map of India. In which form are the deposits found? Discuss in the class.
Hint:
Iron is found as haematite ore, aluminium as bauxite and zinc as zinc blende or zinc carbonate.

Question 5.
Discuss with your parents/ neighbours/goldsmiths why gold is preferred for making jewellery.
Hint:
Gold is the most ductile and least reactive metal with large amount of lustre.

Activity 1

Objective: To show that the oxides of non¬metals (e.g., sulphur) are acidic in nature.
Materials Required: Powdered sulphur, deflagrating spoon, gas jar, glass cover, water, litmus solution.
Procedure:

• Take a small amount of powdered sulphur in a deflagrating spoon.
• Heat it over a flame.
• As soon as the sulphur starts burning, introduce the spoon into a gas jar.
• Cover the gas jar with a glass cover.
• When the reaction is over, remove the spoon and add 5 mL of water into the jar and replace the glass cover.
• Shake the jar and add about 1 mL blue litmus solution in it.
• Shake it and observe the colour change.

Observation: When the solution of sulphur is mixed with blue litmus, it turns red.
Conclusion: Sulphur is a non-metal and its oxide is acidic in nature.

ii. Reaction with Water:
Metals: When a metal reacts with water, a metal hydroxide and hydrogen gas are formed. Different metals react with water at different temperatures. Some metals react vigorously with water, while some others do not react with water at all.
Metal + Water → Metal hydroxide + Hydrogen

Example: Sodium is a highly reactive metal and reacts vigorously with water. This is a highly exothermic reaction. During this reaction, sodium catches fire because of too much heat being evolved. Due to this, sodium is stored in kerosene to prevent accidental fires.

Non-metals: Generally, non-metals do not react with water though they may be very reactive in air. Some non-metals, such as phosphorus, react with air vigorously. It catches fire if exposed to air. Hence, phosphorus is stored in water.

iii. Reaction with Acids:
Metals: Metals give hydrogen gas every time they react with a dilute acid.
Metal + Acid → Metal salt + Hydrogen
Example: Zinc gives hydrogen gas along with zinc chloride when it reacts with hydrochloric acid.

Similarly, zinc also gives hydrogen gas when it reacts with sulphuric acid.
Also, metals like copper do not react with dilute sulphuric acid even on heating but it reacts with concentrated sulphuric acid.

Non-metals: Non-metals do not react with acids.

Activity 2

Objective: To show the reaction of metals and non-metals with dilute hydrochloric acid and dilute sulphuric acid.
Materials Required: Test tube, metals and non-metals (magnesium ribbon, aluminum foil, iron filings, charcoal and sulphur powder), hydrochloric acid, sulphuric acid and matchbox.
Procedure:

• Take a samples of metals and non-metals in separate test tubes and label them as A, B, C, D and E.
• With the help of a dropper, add 5 mL of dilute hydrochloric acid to each test tube one by one.
• Observe the reaction carefully. If no reaction occurs in the cold solution, warm the test tube gently.
• Bring a burning match stick near the mouth of each test tube.
• Repeat the same activity using dilute sulphuric acid in place of dilute hydrochloric acid.

Observations:

Conclusion: Metals usually displace hydrogen from dilute acids and liberate hydrogen gas while non-metals do not react with dilute acids and no hydrogen gas is evolved.

iv. Reaction with Bases:
Metals: Metals give hydrogen gas when they react with a base. This gas produces a pop sound when a burning matchstick is put above the mouth of the beaker containing reaction mixture.
Example: Aluminium metal reacts with sodium hydroxide to fonn hydrogen gas and sodium aluminate.

Non-metals: Reactions of bases with non-metals are complex.
Aqua regia: It is a freshly-prepared solution of concentrated HCl and concentrated HNO₃ in the ratio of 3 : 1 respectively. It can dissolve even gold and platinum.

Displacement reaction: When a more reactive metal displaces a less reactive metal from its salt solution, it is called a displacement reaction.
Metal A + Salt solution of metal B → Salt solution of metal A + Metal B
In the above equation, metal A is more reactive than metal B, so B will be displaced.

Example 1: When aluminium metal is dipped in the solution of copper sulphate, it forms aluminium sulphate and copper.

Example 2: When iron reacts with solution of copper sulphate, it gives iron sulphate and copper.

In the above two reactions, aluminium and iron are more reactive than copper, that is why they displaced copper from the copper sulphate solution.

Activity 3

Objective: To show displacement reaction with the help of an activity.
Materials Required: Five beakers (100 mL), water, zinc sulphate, iron sulphate, copper sulphate, zinc granules, iron nails and copper turnings
Procedure:

• Take five 100 mL beakers and label them as A, B, C, D and E.
• Take about 50 mL of water in each beaker.
• Dissolve in beakers A and B, a teaspoonful of copper sulphate (CuSO₄), in beakers C, D and E zinc sulphate (ZnSO₄), iron sulphate (FeSO₄) and zinc sulphate (ZnSO₄), respectively.
• Put zinc granules, iron nail, copper turnings, copper turnings and iron nail in beakers A, B, C, D and E, respectively.
• Observe the changes.

Reactions:
A : CuSO₄ + Zn → ZnSO₄ + Cu
B : CuSO₄ + Fe → FeSO₄ + Cu
C : ZnSO₄ + Cu → No change
D : FeSO₄ + Cu → No change
E : ZnSO₄ + Fe → No change

Observation: We see that in beakers A and B, colour is changed while in C, D and E, there is no change of colour. Beakers A and B show displacement reactions.

Conclusion: We have seen that only a more reactive metal displaces a less reactive metal from its salt solution but a less reactive metal does not do so.

Uses of Metals:
i. Metals are used in making wires and sheets, which are used for various purposes. For example, copper and aluminium wires are used for the conduction of electricity, in electrical equipments, etc. Iron wires are used for fencing and various other purposes. Iron sheets are often used for making roof sheds.
ii. Metals are used in making machinery, automobiles, utensils, industrial gadgets, water boilers, etc.
iii. Some metals like iron, sodium and calcium are essential parts of our body.
iv. Alloys: An alloy is a solid mixture of two or more metals or a metal and a non¬metal.
a. Alloys of metals are used in making coins, satellites, stainless steel, wooden ships sheathing and casting. For example, Muntz is an alloy of 60% Cu and 40% Zn. Similarly, brass is an alloy of copper and zinc.
b. Alloys like duralumin, have great strength. It is used in aircrafts, pressure cookers, automobiles, etc. Naval brass is used for marine and engineering castings.

Uses of Non-metals:

• The number of non-metals is very less in comparison to metals, but non-metals are very useful for us. So far, only about 22 non-metals have been discovered.
• Non-metals, such as oxygen, are essential for our life which all living being inhale during breathing.
• Sodium chloride (common salt) cannot be formed without chlorine (a non¬metal) which is a necessary ingredient of our food.
• Non-metals are used in fertilisers to enhance the growth of plants. For example, NPK fertilisers.
• They are also used in water-purification process. Chlorine, a non-metal, is used as a disinfectant in water treatment plants.

Class 8 Science Chapter 4 Materials: Metals and Non-Metals Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define metal.
Answer:
Metal is usually a hard substance which is lustrous, sonorous, ductile and is a good conductor of heat and electricity.

Question 2.
Define non-metal.
Answer:
Non-metal is a substance which is usually soft, non-lustrous, non-sonorous, non-ductile and is a bad conductor of heat and electricity.

Question 3.
What is lustre?
Answer:
The typical shine of a metal is called lustre.

Question 4.
Name two metals which can be cut with a knife?
Answer:
Sodium and potassium.

Question 5.
Name a non-metal which is a good conductor of electricity.
Answer:
Graphite.

Question 6.
An element forms an oxide which is acidic in nature. Is the element a metal or a non-metal?
Answer:
Non-metal.

Question 7.
Give the chemical equation representing the reaction of iron with oxygen.
Answer:
2Fe + O₂ + H₂O → Fe₂O₃.xH₂O

Question 8.
What is the chemical formula of magnesium oxide?
Answer:
MgO.

Question 9.
Do metals also react with bases?
Answer:
Metals also react with bases like sodium hydroxide and produce hydrogen gas.

Question 10.
What is the chemical formula of copper hydroxide?
Answer:
Cu(OH)₂.

Question 11.
What are metalloids?
Answer:
The elements which show the properties of both metals and non-metals e.g., silicon and arsenic, are called metalloids.

Question 12.
What is a displacement reaction?
Answer:
It is a reaction in which a more reactive metal displaces a less reactive metal from its salt solution.

Question 13.
Give an example of a displacement reaction.
Answer:
CuSO₄ (copper sulphate) + Zn (Zinc) → ZnSO₄ (Zinc sulphate) + Cu (Copper).

Question 14.
Give the name of one metal and one non-metal which exist in liquid state.
Answer:
Mercury (liquid metal) and bromine (liquid non-metal).

Short Answer Type Questions

Question 1.
Copper coins develop greenish patches when kept unused for a long time. Why?
Answer:
When copper is exposed to moist air for a long time, it acquires a greenish coating. The green coat is a mixture of copper hydroxide and copper carbonate which is formed as a result of reaction of copper with moist air.
2Cu + H₂O + CO₂ + O₂ → Cu(OH)₂ + CuCO₃
Due to this, copper coins develop greenish patches when kept unused for a long time.

Question 2.
What happens when a magnesium ribbon is heated in the presence of air?
Answer:
Magnesium bums with a bright dazzling light in the presence of oxygen and forms a white powder of magnesium oxide.
2Mg(s) + O₂(g) → 2MgO(s)

Question 3.
How does a base react with metals and non-metals?
Answer:
Reaction of base with metals and non-metals is as follows:
a. Metals react with bases to produce metal salt and hydrogen gas.
For example: Aluminium + Sodium hydroxide → Sodium aluminate + Hydrogen gas
b. Reaction of non-metals with bases is much complex.

Question 4.
What happens when zinc granules are kept in copper sulphate solution?
Answer:
When zinc granules are kept in copper sulphate solution, the blue colour of copper sulphate disappears and the solution becomes colourless. Zinc is more reactive than copper and hence displaces copper from copper sulphate solution and forms zinc sulphate solution which is colourless.
CuSO₄ (Blue) + Zn → ZnSO₄ (Colourless) + Cu

Question 5.
What happens when copper turnings are kept in zinc sulphate solution?
Answer:
Copper is less reactive than zinc. Hence, copper cannot displace zinc from its salt solution. Hence, no reaction takes place when copper turnings are kept in zinc sulphate solution.

Question 6.
Explain an activity to test the nature of rust.
Answer:
Collect some quantity of rust after a reaction between iron, oxygen and water. Dissolve it in a very little amount of water. Shake the mixture of rust and water well. Test the solution with red and blue litmus papers. It will be observed that the red litmus paper turns blue. It shows that the nature of rust is basic.

Question 7.
Metals are good conductor of electricity. Explain this with the help of an activity.
Answer:
Make an electric circuit as shown in the given figure. The circuit is used to test whether electricity can pass through a given material or not. Repeat this activity with different materials as shown in the table. Observe whether the bulb glows or not in each case and identify whether they are good or bad conductors of electricity.

It will be observed that iron rod/nail and copper wire are good conductors while rolled sulphur piece and coal piece are bad conductors.

Question 8.
Explain the reaction of sodium with water with the help of an activity.
Answer:
Take a 250 mL beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in small pieces of cotton. Put the sodium piece wrapped in cotton into the beaker. Observe carefully. During observation, keep yourself away from the beaker. When reaction stops, touch the beaker. Now test the solution with red and blue litmus papers. The solution turns red litmus into blue.

This activity indicates that sodium is highly reactive and it reacts vigorously with water. A lot of heat is generated in the reaction to form basic solution of sodium hydroxide.
Sodium + Water → Sodium hydroxide + Heat

Question 9.
Have you ever seen a blacksmith beating an iron piece? Find a change in the shape of these pieces on beating. Would you expect a similar change in a wood log on beating?
Answer:
Yes, we have seen blacksmith beating the iron pieces. We have seen the changes in the shape on beating. It increases in size and it does not break. A similar change in a wood log cannot be expected at all. A wood log will break into pieces if beaten.

Question 10.
State three reasons (of which at least one must be chemical) for believing that sulphur is a non-metal.
Answer:

1. Sulphur is neither malleable nor ductile. It cannot be hammered into sheets or drawn into wires. Sulphur is brittle and breaks into pieces when hammered.
2. Sulphur does not conduct electricity.
3. Sulphur forms an acidic oxide, i.e., sulphur dioxide, hence it is a non-metal.

Question 11.
Concentrated sodium hydroxide solution cannot be stored in aluminum containers. Give reasons.
Answer:
Aluminium metal will react will NaOH base and liberate highly inflammable hydrogen gas.
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂
Hence, sodium hydroxide solution cannot be kept in aluminium containers.

Question 12.
What happens when metals react with dilute acids? Write equations of the reactions of magnesium and zinc metals with dilute hydrochloric acid.
Answer:
Metals form their respective salts when they react with dilute acids and liberate hydrogen gas.
Metal + dilute acid → Metal salt + Hydrogen

a. Reaction of magnesium metal with dilute hydrochloric acid:
Magnesium chloride and hydrogen gas are formed when magnesium reacts with dilute hydrochloric acid.
Mg + 2HCl → MgCl₂ + H₂

b. Reaction of aluminium with dilute hydrochloric acid: Aluminium chloride and hydrogen gas are formed.
2Al + 6HCl → 2AlCl₃ + 3H₂

Question 13.
A solution of copper sulphate was kept in an iron pot. After a few days, the iron pot was found to have a number of holes in it. Write the reaction that took place. Explain this reaction.
Answer:
Iron is more reactive than copper. Iron displaces copper from copper sulphate solution and forms iron sulphate. Hence, holes appear on the pot as iron gets dissolved in the solution.
Fe + CuSO₄ (aq) → FeSO₄ (aq) + Cu

Question 14.
Why are aluminium and zinc known as self protecting metals?
Answer:
Aluminium and zinc are self protecting metals because when they come in contact with air, they form their respective oxides that form an impermeable layer on their surface which prevents further attack of air on the metal.

Long Answer Type Questions

Question 1.
What is the difference between the chemical properties of metals and non-metals?
Answer:

Question 2.
State five uses each of metals and non-metals.
Answer:
Uses of metals:

• Lead metal is used in making car batteries.
• Zinc is used for galvanizing iron to protect it from rusting.
• Iron, copper and aluminium are used to make utensils.
• Copper and aluminium metals are used to make electrical wires.
• Aluminium is used to make aluminium foil for packing food materials.

Uses of non-metals:

• Hydrogen is used in the hydrogenation of vegetable oils.
• Carbon is used to make electrodes of electrolytic cells and dry cells.
• Nitrogen is used in the manufacture of ammonia, nitric acid and fertilisers.
• Sulphur is used for producing sulphuric acid.
• Liquid hydrogen is used as rocket fuel.

Question 3.
You are given samples of three metals-sodium, magnesium and copper. Suggest any two activities to arrange them in order of their decreasing reactivities.
Answer:
a. Activity 1: When sodium, magnesium and copper are left in air, sodium reacts vigorously with oxygen to form sodium oxide, magnesium reacts with oxygen to form magnesium oxide only on heating, whereas copper does not bum in air even on strong heating. It reacts only on prolonged heating. This shows that sodium is most reactive, then magnesium and copper is the least reactive among the three.

b. Activity 2: Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen, magnesium does not react with cold water but reacts with hot water to form magnesium hydroxide and hydrogen but copper does not react even with steam. This shows that sodium is highly reactive, magnesium is less reactive than sodium and copper is the least reactive among the three.

Picture-Based Questions

Question 1.
Observe the given diagram and answer the following questions:

a. Which property of metals is shown by this diagram?
b. Name two metals, other than iron, which have this property.
c. Name a non-metal which has this property.
Answer:
a. The given diagram shows the property of electrical conductivity of metals.
b. Copper and silver.
c. Graphite.

Question 2.
Observe the given figure and answer the following questions:

a. Which property of metals is shown in the figure?
b. Names the articles shown in the figure.
c. Name two metals which show this property.
d. Name two metals which lack this property.
Answer:
a. In the given figure, the property of malleability of a metal is shown.
b. Hammer and iron nails.
c. Gold and silver.
d. Sodium and potassium.

These NCERT Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Synthetic Fibres and Plastics NCERT Solutions for Class 8 Science Chapter 3

Class 8 Science Chapter 3 Synthetic Fibres and Plastics Textbook Exercise Questions and Answers

Page 41-42

Question 1.
Explain why some fibres are called synthetic.
Answer:
Some fibres are called synthetic fibres because they are man-made. These fibres are made by the combination of different types of chemicals in industries and their properties are also different from those of the natural fibres. Some of the examples of synthetic fibres are nylon, rayon, acrylic, polyester, etc.

Question 2.
Mark (✓) the correct answer. Rayon is different from synthetic fibres because
a. it has a silk-like appearance.
b. it is obtained from wood pulp.
c. its fibres can also be woven like those of natural fibres.
Answer:
b. it is obtained from wood pulp.

Question 3.
Fill in the blanks with appropriate words.
a. Synthetic fibres are also called …………… or …………… fibres.
b. Synthetic fibres are synthesised from raw material called ……………
c. Like synthetic fibres, plastic is also a ……………
Answer:
a. artificial, or man-made
b. petrochemicals,
c. polymer

Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
Nylon is used for making parachutes. A parachute needs to be strong as it has to withstand high speed wind and huge amount of air pressure. Nylon ropes are used by mountaineers. A mountaineer’s life highly depends on the strength of ropes he is using. These examples show that nylon fibres are very strong.

Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Plastic does not react with most of the substances. Hence, food kept in plastic container remains fresh for longer duration. Due to this, plastic containers are preferred for storing food.

Question 6.
Explain the difference between thermoplastic and thermosetting plastic.
Answer:

Question 7.
Explain why the following are made up of thermosetting plastics.
a. Saucepan handles
b. Electric plugs/switches/plugboards
Answer:
a. Thermosetting plastic is fire-resistant and can withstand very high temperatures. Due to this, saucepan handles are made up of thermosetting plastic. Such handles do not heat up during cooking,

b. Thermosetting plastic is a bad conductor of electricity and heat. Hence, electric plugs, switches and plugboards are made up of thermosetting plastic.

Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:

• Can be recycled: plastic toys, ballpoint pens, plastic bowls, plastic chairs, carry bags, plastic covering on electrical wires.
• Cannot be recycled: Cooker handles, telephone instruments, electrical switches.

Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
A shirt made from synthetic materials does not allow air to pass through it. On the other hand, a shirt made from cotton allows air to pass through it. Also, water from cotton evaporates easily, causing a cooling effect while a synthetic fibre retains moisture leading to humidity in summers. Hence, a cotton shirt keeps the body temperature lower. Hence, a cotton shirt is more comfortable in summers than a shirt made from synthetic material. Therefore, Rana should buy a cotton shirt.

Question 10.
Give examples to show that plastics are non-corrosive in nature.
Answer:
We know that acids and bases are corrosive in nature. Nowadays, many acids and bases are stored in plastic containers. This is possible because of non-corrosive nature of plastic. A plastic chair does not get rusted like an iron chair does. This also happens because of the non-corrosive nature of plastic.

Question 11.
Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer:
Purpose of the handle of a toothbrush is different from the purpose of bristles of the toothbrush. The handle needs to be strong and less flexible. The bristles need to be highly flexible, soft yet durable. Hence, bristles need to be made up of a different material than the material of toothbrush handle.

Question 12.
‘Avoid plastics as far as possible’. Comment on this advice.
Answer:
We know that plastic is non-biodegradable. This means that plastic waste keeps getting accumulated in our environment. Accumulation of plastic waste is creating a huge problem for us. Hence, we should avoid plastic as far as possible. We should switch over to biodegradable alternatives wherever possible. For example, we should use shopping bags made up of jute or cloth instead of plastic. If plastic is burnt it releases poisonous gases and the plastic bags thrown in the garbage dump are swallowed by animals. They choke their respiratory system and this causes fatalities in animals.

Question 13.
Match the terms of column A correctly with the phrases given in column B.

Answer:
(i) → (d),
(ii) → (c),
(iii) → (a),
(iv) → (b)

Question 14.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Answer:
Synthetic fibres have replaced natural fibres for most uses. It has resulted in reducing our dependency on natural fibres. Many natural fibres come from plants and hence plants need to be cut down to obtain these fibres. Less demand for natural fibres means there is a reduced need to cut down the trees. It has helped in conservation of forests. Hence, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.

Question 15.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
For this, take a small piece of thermoplastic, some copper wires, two electric cells and an electric bulb (from torch).

• Connect the bulb with the battery and attach the thermosetting plastic to wires to make a circuit.
• It is observed that the bulb does not glow.
• When thermosetting plastic is replaced with a metal rod in the circuit, the bulb begins to glow.
• This shows that thermosetting plastic is a poor conductor of electricity.

Caution: Do this activity in the presence of your teacher or parent.

NCERT Extended Learning Activities and Projects

Question 1.
Have you heard of the campaign: “Say No to Plastics”. Coin a few more slogans of this kind. There are certain governmental and non-governmental organisations who educate general public on how to make a wise use of plastics and develop environment friendly habits.
Find out organisations in your area which are carrying out awareness programmes. If there is none, form one.
Hint.
Related slogans:
a. “Don’t laminate the earth!”
b. “Eating plastic, animals died; seeing plastic, nature cried. So, say no to plastics!”
c. “Plastics are dangerous which spoil the river. After some days we will shiver.”

There are many organisations which carry out awareness programmes such as Bharat Seva Sangh [established in 2000], Sewak (established in 1998), Aarti (established in 2009), MUSS (Manav Uthhan Seva Sansthan) (established in 2001).

Question 2.
Organise a debate in the school. Children may be given an option to role play as manufacturers of synthetic fabrics or those of fabrics from natural sources. They can then debate on the topic ‘My Fabric is Superior’.
Hint.
The clothes which we wear are made up of fabrics. Fabrics are made from fibres obtained from natural or artificial sources. Fibres are obtained from four main sources: animal (wool, silk), plant (cotton, flax, jute), mineral (asbestos, glass fibre) and synthetic (nylon, polyester, acrylic). Fibres are also used for making a large variety of household articles.

Question 3.
Visit five families in your neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them in terms of cost, durability and maintenance. Make a short report and submit it to your teacher.
Hint:
Do it yourself.

Question 4.
Devise an activity to show that organic waste is biodegradable while plastic is not.
Hint:
Activity: Collect garbage from your house before it is thrown into the dustbin. Separate the garbage into two groups.

In group 1, include wastes such as polythene bags, chips packets, empty plastic bottles, plastic toys, etc. In group 2, include only kitchen wastes like peels of fruits and vegetables, waste food, newspaper and garden wastes like dead leaves and other plant parts. Bury these materials separately in two pots and label them as A and B. Remove the top soil after one week and check the status of the garbage. Then approximately after four weeks, check the condition of the garbage again.

It will be observed that the waste in pot B decomposes, while the waste in pot A does not decompose.

This shows that the waste (plastic) kept in pot A is non-biodegradable, while the waste (organic waste) kept in pot B is biodegradable.

Activity 1

Objective: To show that the nylon thread is stronger than cotton, wool, silk and polyester threads.
Materials Required: Different threads (cotton, wool, silk, nylon and polyester), iron stand and pan.
Procedure:

• Take an iron stand with clamp.
• Take a cotton thread of about 60 cm length.
• Tie it to the clamp so that it hangs freely from it as shown in the figure.
• At the free end, suspend the pan so that weight can be placed on it.
• Add weight one by one till the thread breaks.
• Note down the total weight required to break the thread. This weight indicates the strength of the fibre.
• Repeat the same activity with threads of wool, silk, polyester and nylon.

Observation: It can be observed that more weight is required to break the nylon thread in comparison to wool, silk, cotton and polyester threads.
Conclusion: Nylon thread is stronger than any other thread.

i. Polyester: Polyester is made up of repeating units of a chemical called ester. The fibres of polyester do not get wrinkled easily, remain crisp and easy to wash. They are used for making clothes, curtains and dress materials. Terylene, when blended with cotton, is called terry cot while with wool it gives terry wool. Clothes made up of such polymers are convenient to use.

PET (Polyethylene terephthalate) is another example of a polyester. It is used for making bottles, utensils, films, wires and many other items. Polyester fabrics do not wrinkle easily and are easy to wash.

iv. Acrylic: Acrylic resembles wool and hence is also called as synthetic wool. It is cheaper and more durable than wool and is easier to wash and maintain.

Characteristics of Synthetic Fibres

• Synthetic fibres are cheaper, stronger and more durable than natural fibres.
• These are easy to maintain, easy to wash, dry up in less time and readily available.
• These fibres possess unique characteristics which make them popular dress materials.

Activity 2

Objective: To study and compare the water absorbing property of natural and synthetic fibres.
Materials Required: Two types of cloth (cotton and polyester), water, and mug.
Procedure:

• Soak the two cloth pieces in different mugs containing same amount of water.
• Now, take out the cloth pieces after five minutes and spread them in the Sun.
• Compare the amounts of water remaining in the mugs.
• Also compare the dryness of both the cloth pieces after keeping in Sun for a few minutes.

Observation: It can be observed that the cotton cloth absorbs more water than the polyester cloth. Also, polyester dries up quickly but cotton does not.
Conclusion: Synthetic libres absorb much less water than the natural fibres.

Plastics: Plastic too is a polymer. However, arrangement of units is different in different types of plastics. In some plastics, the individual units are linked in a linear fashion. In some other plastics, the individual units are cross-linked. Plastic is easily moutdable, recyclable, reusable, colourable, can be melted, rolled into sheets or drawn into wires.

(b) Cross-linked arrangement of units:
Plastic is used in making toys, suitcase, bags, cabinets, brush, chairs, tables and many other countless items. Polythene (Poly + ethene) is one of the most famous examples of plastic, which is used in the manufacturing of carry bags.

Plastics as Materials of Choice: Due to various qualities, plastics are used in our everyday life.

• Plastic is non-reactive: Plastics do not react with water and air due to which they do not get rusted like iron. They are not corroded easily. So, they are used to store various kinds of materials, including many chemicals.
• Plastic is light, strong, cheaper and durable: They are generally cheaper than metals. Hence, they are widely used in industry and household articles.
• Plastic is a poor conductor of heat: Plastics are poor conductors of heat. They are therefore used in making handles of screwdrivers and cooking vessels and in making containers for microwave oven.
• Plastic is poor conductor of electricity: Plastics are poor conductors of electricity and are used in making a cover for electric wires, cables and appliances. Electric switches are made from bakelite.

Plastic and the Environment:
i. Biodegradable: A material which can be decomposed by microbes is called a biodegradable material, e.g., jute, cotton, paper, leftover food, etc.
ii. Non-biodegradable: A material which cannot be decomposed by microbes is called a non-biodegradable material, e.g., plastic, iron, copper, etc.

Plastics take several years to decompose, thus cause environmental pollution.
Burning of synthetic materials releases lots of poisonous fumes into the atmosphere causing air pollution. So, plastics and synthetic fibres are not environment-friendly.

Nuisance of Plastic Bags

• Plastic bag keeps on accumulating in the environment.
• It chokes drains leading to waterlogging.
• A stray animal can die if it accidentally swallows a plastic bag.

How to tackle the problem of plastic waste?

i. Avoid the use of plastics as far as possible.
ii. Follow the 5R principle i.e., Reduce, Reuse, Recycle, Recover and Refuse.
Recycle

iii. Use recyclable plastic or use shopping bags of cloth or jute.
iv. Do not throw plastic bags on roads or in drains.
v. Reuse plastic containers for keeping household items.

Class 8 Science Chapter 3 Synthetic Fibres and Plastics Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are natural fibres? Give examples.
Answer:
The fibres obtained from plants and animals are called natural fibers. For example cotton, silk, jute, etc.

Question 2.
Define polymer.
Answer:
A polymer is a large molecule formed by the combination of many small molecules, each of which is called a monomer.

Question 3.
Name a natural polymer.
Answer:
Cellulose.

Question 4.
What are the monomer units of cellulose?
Answer:
Cellulose is made up of a large number of glucose units.

Question 5.
Name the fibre having properties similar to that of silk.
Answer:
Rayon.

Question 6.
What is polyester?
Answer:
The polymer made up of the repeating units of ester is called polyester.

Question 7.
What is the full form of PET?
Answer:
Polyethylene terephthalate.

Question 8.
What is the full form of PVC?
Answer:
Polyvinyl chloride.

Question 9.
What are plastics?
Answer:
The plastics are a mouldable synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon, etc.

Question 10.
What are the two types of arrangement of units in plastic?
Answer:
Linear linking and cross-linking.

Question 11.
Which synthetic fibre is also known as ‘artificial wool’?
Answer:
Acrylic.

Question 12.
Why is teflon used as a tape for sealing purposes?
Answer:
Because of its toughness, teflon is used as a tape for sealing purposes.

Question 13.
Name the first fully synthetic fibre.
Answer:
Nylon.

Question 14.
Why is nylon used for making parachutes?
Answer:
Nylon is used for making parachutes because it is very strong, elastic and light.

Question 15.
What are petrochemicals?
Answer:
Petrochemicals are the raw materials which are further used to make synthetic fibres.

Short Answer Type Questions

Question 1.
How can polythene carry bags be harmful for animals?
Answer:
Polythene carry bags are thrown here and there after being used. Stray cattle consume them. In this case, it can choke their respiratory system and damage their stomach. It can even cause their death.

Question 2.
Give two disadvantages of synthetic fibres.
Answer:

1. Most synthetic fibers catch fire very easily. Therefore, it is not advisable to wear them near a source of fire,
2. Most synthetic fibers absorb very little moisture. They become sticky when the body sweats, which makes them uncomfortable to wear in hot weather.

Question 3.
Write a short note on acrylic.
Answer:
Acrylic resembles wool and hence is also called synthetic wool. It is cheaper and more durable than wool and is easier to wash and maintain. Acrylic is less expensive and easily available.

Question 4.
What is the difference between nylon and rayon?
Answer:

Question 5.
What do you mean by biodegradable and non-biodegradable materials? Explain with examples.
Answer:

• Biodegradable materials: A material which can be decomposed by the action of microbes is called a biodegradable material, e.g., jute, cotton, paper, leftover food, etc.
• Non-biodegradable materials: A material which cannot be decomposed by the action of microbes is called a non- biodegradable material, e.g., plastic, iron, copper, etc.

Question 6.
What is 5 R principle?
Answer:
5 R stands for:

• Reduce the use of non-biodegradable things.
• Reuse the things again and again.
• Use the thing which can be recycled.
• Recover the lacking substance.
• Refuse the plastics and other harmful articles.

Question 7.
Why has the government banned the use of polythene bags?
Answer:
Polythene or plastic bags are non-biodegradable. It means that they cannot be decomposed or recycled by the action of microorganisms. Besides this, an improper disposal of polythene leads to the following environmental problems:

• Soil and water pollution.
• Blockage and choking of drains and sewer lines.
• Death of animals that chew these polythene bags along with any food.

Question 8.
Why do mountaineers use nylon ropes for climbing the mountains?
Answer:
Mountaineers use nylon ropes for climbing the mountains because nylon is a high strength fibre and does not break easily. It has capacity to bear weight and helps the mountaineers to climb.

Question 9.
What is the chemical nature of polyester? What are polycot and poly wool?
Answer:
Polyester is actually made by the repeating units of a chemical called ester. Esters are the chemicals which give a characteristic fruity smell. Fabrics are sold by the names like poly cot, poly wool, terry cot, etc. As the name suggests, these are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton while poly wool is a mixture of polyester and wool.

Question 10.
Why is polyester quite suitable for making dress materials?
Answer:
Fabric made from polyester does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.

Question 11.
Why has artificial wool become more popular than natural wool?
Answer:
Artificial wool is prepared from a synthetic fibre called acrylic. The material obtained from natural sources is quite expensive whereas materials made from acrylic are relatively cheaper and available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres.

Question 12.
Give three advantages of polythene over natural materials.
Answer:
Three advantages of polythene over natural materials are:

1. It is light, strong and durable.
2. It can be rolled into sheets.
3. It does not react with water and air.

Question 13.
Why is a plastic bucket preferred over an iron bucket?
Answer:
Plastic bucket is preferred over an iron bucket because iron is reactive and it oxidises upon reaction with oxygen and moisture to form rust while plastic is non-reactive and does not form any rust.

Question 14.
Name two polyester fabrics and write their uses.
Answer:
Terylene and PET are polyester fabrics:

• Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yam.
• PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Question 15.
Why should we not wear synthetic clothes while working in kitchen or in a laboratory?
Answer:
Synthetic fibres melt on heating. If the clothes catch fire, it can be disastrous. The fabric will melt and stick to the body of the person wearing it causing bums. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.

Question 16.
Differentiate between natural and synthetic fibres.
Answer:

Question 17.
Describe the characteristic features of the synthetic fibres.
Answer:
Following are the characteristic features of synthetic fibres:

• Raw materials: All synthetic fibres are made from chemicals. They are prepared by a number of processes using raw materials of petroleum family called petrochemicals.
• Strength: Synthetic fibres are quite strong, e.g., nylon.
• Durability: Synthetic fibres are quite durable. They do not wither easily.
• Soak less water: Synthetic fibres absorb small quantities of water and lose it quickly. Hence, they dry up very soon.
• Availability and cost: Synthetic fibres are less expensive and readily available.

Long Answer Type Questions

Question 1.
Explain the discovery and unique features of nylon.
Answer:
Nylon was synthesized in 1935 by Wallace Carothers in DuPont’s research laboratory. The term ‘nylon’ has been derived from the letters of ‘New York’ and ‘London’. No ingredient from plant or animal source was used in making nylon. It was made from coal, water and air. Hence, nylon is called the first truly synthetic fibre. Some of its unique features are as follows:

• Nylon is strong, light and elastic.
• It is lustrous and easy to wash.
• Nylon is used in many articles, like socks, bags, toothbrushes, ropes, sneakers, parachutes, etc.
• For the same thickness, a nylon thread is stronger than a steel wire.

Question 2.
Explain different types of plastics and their uses.
Answer:
Different types of plastic and their uses are as follows:
a. Thermoplastic: Some plastics get easily deformed on heating, and can be easily bent and re-shaped. They are called thermoplastics. Polythene and PVC are examples of such plastics. Thermoplastic is used for making combs, toys, buckets, mugs, etc.

b. Thermosetting Plastic: Some plastics do not get deformed on heating, and cannot be re-moulded into a new shape. Such plastics are called thermosetting plastics. Bakelite and melamine are examples of thermosetting plastic. Bakelite is used for making electrical switches and electrical switchboards because it is a poor conductor of heat and electricity. Melamine is resistant to fire and is hence used for making utensils.

Question 3.
What are the reasons for the popularity of plastic?
Answer:
Following are the reasons for the popularity of plastic:
a. Plastic is non-reactive: Unlike iron, plastic does not react with air to form rust. Due to this, plastic has replaced iron from many articles. Plastic does not react with many chemicals and hence, plastic containers are used for keeping many materials and chemicals.

b. Plastic is light, strong and durable: Plastic is light-weighted, strong and durable. Plastic chairs have replaced wooden chairs in most of the households. Wooden crates have been replaced by plastic crates for keeping milk and cold drinks. Most of the warehouses now use plastic pellets for keeping goods.

c. Plastic is a poor conductor of heat and electricity: Because of poor conductivity to heat and electricity, plastic is used for making switches and many components of electrical appliances. Handles of utensils are made up of plastic because such handles do not heat up.

Question 4.
Suggest some methods to minimise or limit the consumption of plastics.
Answer:
Some ways to limit plastic consumption are:

• Reducing the use of plastics. Whenever possible, use paper or jute bags instead of plastic or jute bags.
• Reusing it for some other purpose, thereby decreasing its consumption.
• Recycling of plastic. It requires the plastic to be collected, sorted, chopped, melted and remoulded.

Question 5.
Make a table to show the time taken by various types of wastes to degrade.
Answer:
According to the research, following is the estimated time taken by some everyday items to decompose in landfill sites:

Picture-Based Questions

Question 1.
Draw a diagram to show the:
a. Linear arrangement of units in plastic.
b. Cross-linked arrangement of units in plastic.
Answer:

Question 2.
Observe the given articles and name the fibrous material they are made from.

Answer:
a. Plastic food container
b. Bakelite switch
c. Teflon-coated pan