These NCERT Solutions for Class 10 Science Chapter 15 Our Environment Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.
Our Environment NCERT Solutions for Class 10 Science Chapter 15
Class 10 Science Chapter 15 Our Environment InText Questions and Answers
In-text Questions (Page 257)
Question 1.
Why are some substances biodegradable and some non-biodegradable?
Answer:
Some substances are biodegradable because the enzymes released by the micro-organism helps in breaking down the biodegradable wastes but some are non-biodegradable because they can not be broken down by the micro-organism.
Question 2.
Give any two ways in which biodegradable substances would affect the environment.
Answer:
- Biodegradable substances like food materials rancid after some time and produce bad smell and causes air pollution.
- Biodegradable substances causes water pollution and make it unfit for domestic purposes.
Question 3.
Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
- Non-biodegradable substances concentrated at different trophic levels and causes various health problems in human beings and animals.
- Non-biodegradable substances do not break-down by organisms in the simpler substances so they disturb terrestrial and aquatic ecosystems.
In-text Questions (Page 261)
Question 1.
What are the trophic levels? Give an example of a food chain and state the different trophic level.
Answer:
The various links or steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic levels.
For example in the following food chain.
Plants → Deer → Lion
The plants constitute the first trophic level. Deer constitute the second trophic level and Lion constitute the third trophic level. Plants produce their food themselves in presence of sun light so they constitute first trophic level. Deer consume plants so it. constitute second trophic level. Lion consume deer so it constitute third trophic level.
Question 2.
What is the role of decomposers in the ecosystem?
Answer:
Decomposers consume, and thus decompose, the dead Demains of the other organisms i.e, autotrophs and heterotrophs. For example, certain bacteria and fungi break down the complex compounds present in the dead organisms into simpler-substances. Through the decomposers the elements enter the earth again, which are in turn again taken up by the plants. So, the cycle of exchange of matter continues. By their activity, the decomposers also maintain soil fertility.
In-text Questions (Page 264)
Question 1.
What is ozone and how does it affect any ecosystem?
Answer:
Ozone (O2) is a molecular gas formed by three atoms of oxygen. While O2, which we normally refer to as oxygen, is essential for all aerobic forms of life, ozone is a deadly poison. However at the higher levels of the atmosphere, ozone performs an essential functions, it shields the surface of the earth from ultraviolet radiation from the sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
Is stratosphere ozone form a layer, known as ozone layer which protect us from harmful ‘UV’ rays of Sun. But due to some holes in the ozone layer ‘UV’ rays are reaching on earth and increasing its temperature. The increase in temperature of earth is causing global warming. So ozone can affect all ecosystems on earth.
Question 2.
How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
With the growing population, the generation of wastes is increasing day by day. Increased use of disposable items is also in favour of increasing waste. The problem of waste disposal can be reduced as follows :
- By using disposable paper cups.
- By using disposable cups made of clay or by using steel.
Class 10 Science Chapter 15 Our Environment Textbook Questions and Answers
Page no. 264
Question 1.
Which of the following groups contains only biodegrable items ?
(a) Grass, flower, leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer:
(d) Cake, wood and grass.
Question 2.
Which of the following constitute a food- chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer:
(b) Grass, goat and human
Question 3.
Which of the following are environment-friendly practices?
(a) Carrying cloth bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer:
(d) All of the above
Question 4.
What will happen if we kill all the organisms in one trophic level?
Answer:
The various lins or steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic’ levels. For examples, plants constitute the first trophic level and the herbivores consumer plants e.g, deer or cow they constitute second trophic level. Lion consume deer, so lion consitute third trophic lelve. If we kill all the organisms of the one trophic level then food or energy cannot be transferred to the next trophic level and the organisms of this trophic level and all organisms of next to this trophic level will suffer for survival.
Question 5.
Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer:
Yes the impact of removing all the organisms in a trophic level will be different for different trophic level. For example, let all the organisms of third trophic level has been removed, so the number of organisms of second trophic level will be increased with a great number and they will consume large quantity of first trophic level so the quantity of first trophic level decreases sharply. No the removal of organisms of any trophic level causes damage to the ecosystem.
Question 6.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer:
Unknowingly some harmful chemical enter our body through the food chain such as pesticides, weedicides and rodenticides etc. These chemicals are either washed down into the soil and finally enter the water or are taken up from the soil by the plants along with water and minerals and thus enter the food chain. As these chemicals are not degradable, these harmful chemicals get concentrated at each trophic level. This is known as biomagnification or biological magnification.
The levels of the magnification will be different at different trophic levels of the ecosystem. The animals at the highest trophic level or the extreme right side of the food chain have the maximum concentration of harmful chemicals in the body.
Question 7.
What are the problems caused by the non-biodegradable wastes that we generate?
Answer:
The waste materials which cannot be broken down to non-poisonous substances easily are called non-biodegradable wastes. Bacteria and other saprophytes cannot break down such wastes. For example, DDT, plastics, polythene bags, synthetic fibre, glass, aluminium cans, iron nails and radioactive (nuclear) wastes.
Non-biodegradable waste cause the following problems :
1. Poisonous chemicals like DDT and other pesticides remain as such in the biosphere for a long time. These enter the food chain where they get biomagnified at each trophic level.
2. Industrial or mining wastes are toxic and cumulative in their harmful effects. Accumulation of metals contain by industrial wastes in a human body can cause permanent damage to the human systems.
3. Polychlorinated biphenyls are resistant to oxidation and highly stable. These are used in transformers and capacitors. Release of PCBs in the air causes skin disorders. They are reported to be carcinogenic.
4. Nuclear radiations causes somatic effects ie, it lead to deadly diseases like cancer and genetic disorders.
Question 8.
If all the waste we generate is biodegradable will this have no impact on the environment?
Answer:
Waste that can be broken down to non-poisonous or harmful substances by the action of certain micro-organism are called biodegradable wastes. The enzymes released by microorganisms helps in breaking down the biodegradable wastes.
Waste in any form i.e., biodegradable or non-biodegradable have an impact on the environment. So we cannot say that if all the waste is biodegradable it will not have any impact on the environment.
Question 9.
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:
The most important gas present in the stratosphere is ozone. At an altitude of about 23 km, its concentration is about 10 ppm.
Ozone absorbs ultraviolet radiation coming from the sun and thus protect us from the harmful effects of the ultraviolet radiation, Ultraviolet rays are known to cause skin cancer, eye damage and damage to the immune system. It also kills the minute aquatic plant life, the phytoplanton. But the amount of ozone in the atmosphere began to drop sharply in 1980s. This decrease has been linked to synthetic chemicals like CFCs which are used as refrigerants and is fire extinguishers. Ozone is a very reactive compelem and it oxidise CFCs. In doing so, ozone is converted into gain oxygen.
Ozone + CFG → Oxygen + Oxidation
Thus ozone layer is depleled and it allows the harmful radiations i.e., ‘UV’ radiations on earth which cause so many negative effect on human beings, which are already discussed. So depletion of ozone layer is harmful for living things on earth.
Control Measures:
- By reducing the use of CFCs, many countries have already banned the use of CFCs.
- By developing substitutes to replace CFCs. These include the compounds called hydro-fluoro-carbons (HFC-134), hydro-chlorofluro-carbons (HCFCs) and methycyclohexane (MCH).
Class 10 Science Chapter 15 Our Environment Textbook Activities
Activity 15.1 (Page 256)
- Collect waste material from your homes. This could include all the waste generated during a day, like kitchen waste (spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons), waste paper, empty medicine bottles/strips/bubble packs, old and torn clothes and broken footwear.
- Bury this material in a pit in the school garden or if there is no space available, you can collect the material in an old bucket/ flower pot and cover with at least 15 cm of soil.
- Keep this material moist and observe at 15-day intervals.
Question 1.
What are the materials that remain unchanged over long periods of time?
Answer:
The materials that remain unchanged over long periods of time are: Milk packets, empty medicine bottles, broken footwear.
Question 2.
What are the materials which change their form and structure over time?
Answer:
The materials which change their form and structure over time are : spoilt food, vegetable peels, used tea leaves, empty cartoons, waste paper, strips, bubble packs, old and tom clothes.
Question 3.
Of these materials that are changed, which ones change the fastest?
Answer:
Spoilt food changed the fastest.
Activity 15.2 (Page 257)
Question 1.
Use the library or internet to find out more about biodegradable and non-biodegradable substances.
Answer:
The substances that are broken down by biological processes are called biodegradable, e.g. food, paper, wood etc.
The substances that are not broken down by biological processes are called non-biodegradable, e.g plastics, rubber etc.
Question 2.
How long are various non-biodegradable substances expected to last in our environment?
Answer:
The non-biodegradable substances may be inert and simply persist in the environment for a long time.
Question 3.
These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment.
Answer:
Now a days a number of new types of plastics are available. These plastics are biodegradable and do not harm the environment.
Activity 15.3 (Page 258)
- You might have seen an aquarium. Let us try to design one.
- What are the things that we need to keep in mind when we create an aquarium? The fish would need a free space for swimming (it could be a large jar), water, oxygen and food.
- We can provide oxygen through an oxygen pump (aerator) and fish food which is available in the market.
- If we add a few aquatic plants and animals it can become a selfsustaining system. Can you think how this happens? An aquarium is an example of a human-made ecosystem.
- Can we leave the aquarium as such after we set it up? Why does it have to be cleaned once in a while? Do we have to clean ponds or lakes in the same manner? Why or why not?
Observation : If we add a few aquatic plants and animals in an aquarium it can be a self sustaining system if animals are able to take food directly from plants otherwise it will not be a sell sustaining system. No we cannot leave the aquarium as such after we set it up An aquarium should be cleaned once in a while because refuse or debris of fish collected in the aquarium can pollute the water of the aquarium. No, we do not have to clean ponds or lakes in the same manner because these cover a large area and many organisms living in it can die.
Activity 15.4 (Page 259)
Question 1.
While creating an aquarium did you take care not to put an aquatic animal which would eat others? What would have happened otherwise?
Answer:
While creating an aquarium we should take care not to put an aquatic animal which would eat other because after consuming all animals, carnivores face food crisis and lastly they will die.
Question 2.
Make groups and discuss how each of the above groups of organisms are dependent on each other.
Answer:
We know that organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment.
Question 3.
Write the aquatic organisms in order of who eats whom and form a chain of at least three steps.
Answer:
Phytoplanktons → Zooplanktons → Small fish.
Question 4.
Would you consider any one group of organisms to be of primary importance? Why or why not?
Answer:
In aquatic system phytoplanktons (algae) are basically needed because they are producers.
Activity 15.5 (Page 261)
1. Newspaper reports about pesticide levels in ready-made food items are often seen these days and some states have banned these products. Debate in groups the need for such bans.
2. What do you think would be the source of pesticides in these food items? Could pesticides get into our bodies from this source through other food products too?
3. Discuss what methods could be applied to reduce our intake of pesticides.
- The chemical substances that are used to kill, or block the reproductive process in harmful organisms such as rodents, insects, mites, bacteria, fungi etc. are called pesticides.
- There is an international standard for the use of pesticides in food items to protect them from bacteria, fungi etc. But in India the quantity of pesticides added in food items is more than hundred times as compared to international standard. That is why some states banned these products. Pesticides are highly harmful for health so a ban is justified on ready-made food items containing a high level of the pesticides.
- Basically the pesticides are added in food items to protect from bacteria and fungi during their preparation. In our bodies pesticides can enter through food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration get accumulated in our bodies.
- An International standard should be followed for the”use of pesticides in food items.
- Natural methods should be preferred to get a good crop.
- Minimum use of pesticides.
- All the vegetables, fruits etc. should be washed with water properly before use. Pulses, rice, grams, etc. should be kept in water for 10-11 minutes and washed 3-4 times with water before cooking,
- Avoid the use of ready-made food items, cold drinks burger etc.
Activity 15.6 (Page 262)
Question 1.
Find out from the library, internet or newspaper reports, which chemicals are responsible for the depletion of the ozone layer.
Answer:
Mainly chlorofluorocarbons (CFCs) ie the compounds of carbon, chlorine and fluorine and ‘NO’ are responsible for the depletion of the ozone layer.
Question 2.
Find out if the regulations put in place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years?
Answer:
The United Nations Environment Programme succeeded in forging an agreement to freeze CFC production at 1986 level. Yes these regulations put in place to control the emission of CFCs and other chemicals have succeeded in reducing the damage to the ozone layer. Yes the size of the ozone layer has changed in the recent years.
Activity 15.7 (Page 262)
Question 1.
Find out what happens to the waste generated at home. Is there a system in place to collect this waste?
Answer:
Two waste generated at home is collected in a dustbin. It is good if the biodegradable and non-biodegradable waste collect separately. So it can be disposed easily.
Question 2.
Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the waste. Are there mechanisms in place to treat the biodegradable and non-biodegradable wastes separately?
Answer:
Generally local body does not treat the bioderadable and non-biodegradable waste separately. Now-a-days in some towns and cities waste material treatment plants are established in which the biodegradable and non-biodegradable wastes are treated separately.
Activity 15.8 (Page 263)
Question 1.
Calculate how much waste is generated at home in a day.
Answer:
In a common family of ‘3-4’ members approximately 2 to 3 kg wastes generated in a day.
Question 2.
How much of this waste is biodegradable?
Answer:
Approximately 70% of this waste is biodegradable.
Question 3.
Calculate how much waste is generated in the classroom in a day.
Answer:
Approximately 1 to 2 kg wastes is generated in the classroom in a day.
Question 4.
How much of this waste is biodegradable?
Answer:
Approximately 80% of this waste is biodegradable.
Question 5.
Suggest ways of dealing with this waste.
Answer:
Bio-degradable wastes generally papers should be burnt in a separate comer of the school and non-biodegradable wastes should be sold so that it can be recycled again like polythene, glass bottles etc.
Activity 15.9 (Page 263)
Question 1.
Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage.
Answer:
The city sewage is the main source of pollution in rivers and takes etc. In our locality it is treated as follows.
The large floating and suspended matter, grit, oil and grease are removed by filtration through screens. The wastewater flows through a channel and the solids retained by the screens are disposed of into the land fields. So to keep our water bodies such as rivers, lakes and nearby seashores clean, the sewage waste must be properly treated before discharging into any water body. So this mechanism ensures that the soil and water are not polluted by untreated sewage.
Question 2.
Find out how the local industries in your locality treat their wastes. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste?
Answer:
In our locality, industries treat wastes as follows:
Basically the treatment of wasles depend on its nature. By recycling process a number of waste material can be treated in different industries such as glass industry, Iron and steel industry etc.
Commonly industries leave water treatment plant to purify waste water and then dump this water into canal or rivers.
Activity 15.10 (Page 263)
Question 1.
Search the internet or library to find out what hazardous materials have to be dealt with while disposing of electronic items. How would these materials affect the environment?
Answer:
Electronic items include T.V. Refrigerators, VCD, VCR, Cooler, A.C., Computer. While disposing electronic items hazardous materials such as glass, plastics etc. should be dealt from the electronic items. Thes materials are non-biodegradable so they pollute soil, water etc.
Question 2.
Find out how plastics are recycled. Does the recycling process have any impact on the environment?
Answer:
When waste plastic material is heated at a high temperature it is melted and can be moulded in desired shape again. Recycling process has a very little impact on the environment because during recycling some vapours are formed which pollute air.
Class 10 Science Chapter 15 Our Environment Additional Important Questions and Answers
Very Short Answer Type Questions
Question 1.
What are the components of environment?
Answer:
- Atmosphere
- Hydrosphere
- Lithosphere
- Biosphere.
Question 2.
Which is the largest Biological system on earth?
Answer:
Biosphere
Question 3.
What is the smallest functional unit of Biosphere?
Answer:
Ecosystem
Question 4.
What is an ecosystem?
Answer:
The functional unit of environment in which living organisms interact with one another as well as with the non-living components.
Question 5.
Give an example of a real natural ecosystem.
Answer:
A pond ecosystem.
Short Answer Type Questions
Question 1.
Explain decomposers or saprophytes with examples.
Answer:
Saprophytes consume both autotrophs and heterotrophs and thus decompose, the dead remains. For example, certain bacteria and fungi break down the complex organic compounds present in the dead organisms into simpler substances. Through the decomposers the elements enter the earth again, which are in turn again taken up by the plants. Thus, the cycle of exchange of matter continues. Decomposers also maintain soil fertility.
Question 2.
How is ozone formed? Give chemical equations.
Answer:
Ozone is formed in the stratosphere. When UV rays falls on oxygen molecules (O2), as a result molecule of oxygen is split into nascent oxygen atoms. These oxygen atoms then combine with the molecular oxygen to form ozone.
Question 3.
What are the causes of Ozone depletion?
Answer:
There are several reasons for the depletion of Ozone layer. The chloroflurocarbons are mainly responsible for depletion of Ozone layer and the other factor is nitrogen monoxide (NO). CFCs are gases which readily solidify when compressed. This makes them useful in refrigeration as propellants in fire extinguishers, in aerosol cans and in plastic foams. CFCs are very stable compounds and accumulate in the upper atmosphere, where they react with ozone. Ozone is a very reactive element and it oxidizes CFCs. In doing so, Ozone is converted into Oxygen.
Ozone + CFC → Oxygen + Oxidation Products.
Nitrogen monoxide (NO) is released in the upper atmosphere from the exhausts of high altitude aircraft. Ozone oxidises nitrogen monoxide to nitrogen dioxide (NO).
Ozone + NO – Oxygen + NO2
Long Answer Type Question
Question 1.
What are the features of an ecosystem?
Answer:
The features of an ecosystem are :
- An ecosystems is a self-sustaining, structural and functional unit of biosphere in which living organisms interact with each other as well as with the abiotic components like air, water and soil.
- It depends on solar energy which is captured by the green plants and passed on to the subsequent heterotrophic organisms Without assures of energy, an ecosystem will not be able to function.
- An ecosystem is an open system in terms of energy and a closed system as flow of minerals is concerned.
- A pond, a lake, a river, a forest, a desert even a man-made aquarium and a crop field are all examples of ecosystems.
Multiple Choice Questions
Question 1.
The flow of energy in a food chain is
(a) unidirectional
(b) Two-directional
(c) Three-directional
(d) Multi-directional
Answer:
(a) unidirectional
Question 2.
The sequential process of eating and being eaten is called
(a) Food web
(b) Food chain
(c) Energy flow
(d) Trophic level
Answer:
(b) Food chain
Question 3.
Man is a
(a) Producer
(b) Carnivore
(c) Herbivore
(d) Omnivore
Answer:
(d) Omnivore
Question 4.
Municipal solid waste, commonly called
(a) Domestic waste
(b) biodegradable waste
(c) garbage
(d) Sewage
Answer:
(c) garbage
Question 5.
Non-biodegradable wastes is/are
(a) Paper
(b) Human excreta
(c) DDT, BHC
(d) Vegetables, Plastic
Answer:
(c) DDT, BHC