NCERT Solutions for Class 7 Science Chapter 2 Nutrition in Animals

These NCERT Solutions for Class 7 Science Chapter 2 Nutrition in Animals Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Nutrition in Animals NCERT Solutions for Class 7 Science Chapter 2

Class 7 Science Chapter 2 Nutrition in Animals Textbook Exercise Questions and Answers

Question 1.
Fill in the blanks.
a. The main steps of nutrition in humans are ……………., ……………., ……………., ……………., ……………..
b. The largest gland in the human body is …………….
c. The stomach releases hydrochloric acid and ……………. juices which act on food.
d. The inner wall of the small intestine has many finger-like out growths called …………….
e. Amoeba digests its food in the …………….
Answer:
a. ingestion, digestion, absorption, assimilation, egestion,
b. liver,
c. digestive,
d. villi,
e. food vacuole.

Question 2.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
a. Digestion of starch starts in the stomach.
b. The tongue helps in mixing food with saliva.
c. The gall bladder temporarily stores bile.
d. The ruminants bring back swallowed grass into their mouth and chew it for some time.
Answer:
a. False,
b. True,
c. True,
d. True.

Question 3.
Tick (✓) mark the correct answer in each of the following:
a. Fat is completely digested in the:
(i) stomach
(ii) mouth
(iii) small intestine
(iv) large intestine
Answer:
a. (iii) small intestine

b. Water from the undigested food is absorbed mainly in the:
(i) stomach
(ii) food pipe
(iii) small intestine
(iv) large intestine
Answer:
b. (iv) large intestine

Question 4.
Match the items of column I with those given in column II:

Column I (Food components)	Column II (Product(s) of digestion)
1. Carbohydrates	(a) Fatty acids and glycerol
2. Proteins	(b) Sugar
3. Fats	(c) Amino acids

Answer:
1. (b),
2. (c),
3. (a).

Question 5.
What are villi? What is their location and function?
Answer:
Villi are the finger-like projections in the inner walls of the small intestine. Villi increase the surface area for absorption of the digested food into the blood.

Question 6.
Where is the bile produced? Which component of the food does it help to digest?
Answer:
The liver secretes bile juice that is stored in a sac called gall bladder. The bile plays an important role in the digestion of fats.

Question 7.
Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Answer:
Cellulose is the carbohydrate that can be digested by ruminants. Ruminants have large sac-like structure called rumen between the small intestine and large intestine. The cellulose of the food is digested by the action of certain bacteria in the rumen which are not present in humans and hence they cannot digest cellulose.

Question 8.
Why do we get instant energy from glucose?
Answer:
We get instant energy from glucose because in the cells, glucose breaks down with the help of oxygen into carbon dioxide and water and energy is released.

Question 9.
Which part of the digestive canal is involved in:
a. absorption of food ____________
b. chewing of food ____________
c. killing of bacteria ____________
d. complete digestion of food ____________
e. formation of faeces ____________
Answer:
a. small intestine,
b. buccal cavity,
c. stomach,
d. small intestine,
e. large intestine.

Question 10.
Write one similarity and one difference between the nutrition in Amoeba and human beings.
Answer:
One similarity is that both Amoeba and humans have holozoic mode of nutrition. The difference is that human beings have complex structures for ingestion, digestion and egestion of food while Amoeba has simple process in which it engulfs the food with the help of pseudopodia and food gets trapped in the food vacuole.

Question 11.
Match the items of column I with suitable items in column II:

Column I	Column II
a. Salivary gland	(i) Bile juice secretion
b. Stomach	(ii) Storage of undigested food
c. Liver	(iii) Saliva secretion
d. Rectum	(iv) Acid release
e. Small intestine	(v) Digestion is completed
f. Large intestine	(vi) Absorption of water
	(vii) Release of faeces

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

Question 12.
Label the diagram of the digestive system.

Answer:

Question 13.
Can we survive only on raw, leafy vegetables/grass? Discuss.
Answer:
No, we cannot survive only on raw, leafy vegetable or grass. It is because the grass contains cellulose which is a type of carbohydrate that humans are not able to digest due to the absence of cellulose-digesting enzymes. Also, we need all the different types of nutrients for our survival and hence it is necessary to take a balanced diet.

NCERT Extended Learning Activities and Projects

Question 1.
Visit a doctor and find out:
a. Under what conditions does a patient need to be on a drip of glucose?
b. Till when does a patient need to be given glucose?
c. How does glucose help the patient recover?
Hint:
a. The various conditions under which a patient needs to be on a drip of glucose are:
i. when the patient is dehydrated.
ii. when the patient is unable to take his food orally.
iii. before doing any type of surgery.

b. A patient should be given glucose only during recovering stage (from any kind of illness).

c. Glucose mixes in the blood instantaneously as it is in the soluble form. Since in patients, the breakdown of food is slowed down due to illness, hence glucose is given because it releases instant energy.

Question 2.
Find out what vitamins are and get the following information.
a. Why are vitamins necessary in the diet?
b. Which fruits or vegetable should be eaten regularly to get vitamins?
Hint:
Vitamins are organic substances that are necessary for normal health and growth in both the animals and the humans. They are required in small quantities in the body.
a. They prevent diseases such as rickets, osteomalacia and scurvy. They promote absorption of calcium and phosphorus compounds from intestines and enable the body to use these information of teeth and bones. Write a one-page note on the information collected by you. You may take help of a doctor, a dietician, your teacher or any other person or from any other source.

b. Fibre rich fruits and vegetables should be eaten. Fruits should be included in our regular diet, especially citrus fruits like orange, lime, grapes, kiwi etc. Vegetables like carrot, beans, beetroot, lady’s finger, cabbage, etc., are rich in all minerals and vitamins, so they should be eaten regularly.

Question 3.
Collect data from your friends, neighbours and classmates to know more about “milk teeth”.
Tabulate your data. One way of doing it is given below:

S. No.	Age at which first tooth fell	Age of which last tooth fell	No. of teeth lost	No. of teeth replaced
1.
2.
3.
4.
5.

Find out from at least twenty children and find the average age at which children lose the milk teeth. You may take help of your friends.
Hint:
Milk teeth are generally shed in 6-8 years of age.

Activity 1

Objective: To study the type of food and mode of feeding of the following animals: snails, ant, eagle, lice, butterfly, housefly, humming-bird, and mosquito.
Procedure: Make a list of various organisms and list their food and mode of feeding as listed below.
Observations:

S. No	Name of the animal	Kind of Food	Mode of Feeding
1.	Snail	Lower plants	Scraping
2.	Ant	Sweets, sugar and flour	Chewing
.3.	Eagle	Rats and birds	Swallowing
4.	Lice	Blood	Sucking
5.	Butterfly	Nectar	Sucking
6.	Housefly	Rubbish	Sponging
7.	Hummingbird	Insects and nectar	Capturing, swallowing and sucking
8.	Mosquito	Blood	Siphoning

Conclusion: Different organisms use different methods to consume food.

Interesting facts: Starfish opens the hard shells of animals on which it preys, like oysters. After opening the shell, the starfish pops out its stomach through its mouth and wraps the stomach around the captured animal. The stomach is then withdrawn into the body and the food is slowly digested.

Animal nutrition is a complex process and involves five important steps:

Ingestion: Ingestion means eating food so as to get energy and carry out the activities of life. Ingestion is the process of taking food into the body.
Digestion: Food that animals eat consists of large insoluble molecules which cannot be absorbed by their body directly. The breakdown of these large insoluble complex molecules, such as carbohydrates, into simpler soluble and usable forms by the body is called digestion.
Absorption: After the food molecules become small and soluble, they pass through the walls of intestine and go into the blood. This process is called absorption
Assimilation: The absorbed food is now carried to all parts of the body and to each and every cell through blood, so as to produce energy and make materials
for the growth and repair of the body. This process is called assimilation.
Egestion: The process through which undigested food is moved out of the body is called egestion.

Digestion in Humans: We take food through our mouth, digest and utilise it with the help of our digestive system.
Human digestive system consists of an alimentary canal and its associated glands. Various organs of human digestive system in sequence are: mouth or buccal cavity, oesophagus (food pipe), stomach, small intestine, large intestine, rectum and anus. Associated with the alimentary canal are some glands that secrete digestive juices. These are salivary glands, liver and pancreas. The alimentary canal along with the associated glands is called the digestive system.

Mouth or Buccal Cavity: We take in food through our mouth and the process of taking food into the body is called ingestion. The mouth consists of teeth, tongue and salivary glands that help in this process.
i. Teeth: Teeth are used for cutting, chewing, grinding and tearing the food before you swallow it. There are four types of teeth in humans- incisors, canines, premolars and molars.

Your front four teeth in each jaw are the incisors. They are used for biting and cutting. Next to incisors are canines. These are pointed and two in number on either side in each jaw. They are used for piercing and tearing the pieces of food.

Premolars are behind the canines, two in number on either side in each jaw. Molars are behind the premolars. They are meant for grinding and crushing the food. In an adult, they are six in number in each jaw, three each on either side of the premolars.

In young adults, there are 8 molars in all. The second set of 4 molars appears at the age eighteen or even later. These are called the wisdom teeth. Each jaw in an adult has 16 teeth. Hence, each adult human has 32 teeth in all.

In humans, the first set of teeth grows during infancy and they fall off at the age of 8-10 years. These are called milk teeth. The second set of teeth grows to replace them and are called permanent teeth.

ii. Tongue: It is a muscular organ attached at the floor of the buccal cavity at the back. It helps in mixing the chewed food with saliva and swallowing the food. The tongue has taste buds. These buds distinguish four basic tastes, i.e., salty, sour, sweet, and bitter. In addition, it helps us to speak.

iii. Salivary glands: The salivary glands present in the mouth secrete watery liquid called saliva. Saliva helps in the digestion of food. It contains an enzyme called salivary amylase (also called ptyalin). Salivary amylase acts on complex starch (a carbohydrate) and changes it into simple sugar in the mouth. Besides, saliva also contains enzymes that kill germs and bacteria that may enter the body along with the food. It also softens and lubricates the food for its easy passage along the alimentary canal.

Activity 2

Objective: To show that certain chemicals digest food.
Materials Required: Test tubes (two), test tube stand (one), water, iodine solution, amylase and a potato.
Procedure:

Place a few potato pieces in a test tube. Add water to it and label this test tube A.
Place the test tube A in the test tube stand.
Place some more potato pieces in the second test tube. Now add water to it. Then add the digestive chemical amylase. Label this test tube B.
Place the test tube B in the test tube stand.
Let both the test tubes stand for 30 minutes, and then add iodine solution to both the test tubes.

Observations: Potato pieces in test tube A turn blue-black while those in test tube B do not.
Conclusion: Digestion has taken place as the starch in test tube B has been acted upon by amylase and hence it does not give starch test.

Oesophagus (Gullet or Food pipe): The swallowed food passes into the food pipe or oesophagus. Hence, oesophagus leads from the mouth to the stomach and it is made up of muscles. The food that we eat is pushed down the oesophagus to the stomach by peristaltic movements that occur all along the alimentary canal.

Stomach: Stomach is the thick-walled bag-like structure present on the left side of the abdomen. It is the widest part of the alimentary canal, and is roughly J-shaped. The stomach walls contain gastric glands which secrete various digestive juices called gastric juices. The stomach walls also secrete mucous and hydrochloric acid. This acid kills the bacteria that may have entered the body with food while the mucous protects the stomach lining from the damage by acid. The digestive juices digest the proteins by breaking them into simpler substances.

Small Intestine: Small intestine is highly 26 coiled and is about 7.5 m long. After leaving stomach, food enters the small intestine and last step of digestion takes place here. In the small intestine, the food is mixed with bile juice and pancreatic juice. Bile is secreted by the liver (a reddish-brown gland) and is stored in gall bladder while the pancreatic juice is secreted by the pancreas (a large cream-coloured gland below the stomach). These juices are important for the process of digestion. While bile helps in digestion of fats, pancreatic juice helps in the digestion of carbohydrates, proteins and fats. In the lower part of the intestine, various intestinal juices are also mixed with the food to complete the process of digestion. Carbohydrates are broken into simple sugars like glucose, fats into fatty acid and glycerol and proteins into amino acids.

Absorption in Small Intestine: The small intestine absorbs the digested nutrients from the food. The inner walls of the small intestine have thousand of finger¬like projections. These are called villi. The surface of the villi are richly supplied with blood vessels and absorb the digested food materials. The villi increase the surface area for the absorption of the digested food into the blood. The digested food is transported in the entire body through blood and assimilated by the cells. Here, glucose is broken down into carbon dioxide and water to release energy with the help of oxygen.

Large Intestine: The undigested and unabsorbed food enters large intestine. Large intestine has no digestive function to carry out. It is about 1.5 m long and helps in absorbing water from the undigested food material.

Rectum: It is the lowermost part of large intestine. The undigested waste material passes into the rectum, where it is sorted as semi-solid faeces. The faecal matter is passed out through the anus by the process of egestion.

Diarrhoea is a disorder of digestive system where a person needs to pass watery stool frequently. It may be caused by the intake of contaminated food or indigestion. Such patients should be given plenty of Oral Rehydration Solution (ORS) which is prepared by dissolving a pinch of salt or sugar in boiled and cooled water.

Digestion In Grass-eating Animals:
Grass-eating animals like cow, buffaloes, goat, sheep, etc., have a separate part of the stomach called rumen. The rumen contains cellulose digesting bacteria. These bacteria, present in the rumen of an animal, helps to digest cellulose (a carbohydrate) present the in grass food eaten by the animal.

The partially digested food in the rumen of an animal is called cud. Rumination is the process by which cud returns to the mouth in a small lump and the animal chews it. When the cud is thoroughly chewed in themouth of the animal, it is swallowed again. The animals which have rumen and carry out rumination are known as ruminants.

Many other animals such as horses, rabbit, etc., have a structure called caecum that helps in digesting cellulose by the action of various bacteria. Many animals, including humans cannot digest cellulose.

Tooth Decay: After eating food items, sweets, chocolates, cold drink and other sugars, if mouth is not washed properly, some leftover food and sugars remain attached to the teeth. The harmful bacteria breakdown these sugars and release acids. These acids gradually damage the teeth. This is called tooth decay which may lead to toothache and even loss of tooth.

Healthy teeth are white and healthy gums are pink. If proper care is not taken, teeth become yellowish due to the formation of a sticky film containing food particles, saliva and bacteria which may lead to loosening of the teeth. Hence, one should brush teeth at least twice daily and should thoroughly rinse the mouth after every meal.

Nutrition in Amoeba: Amoeba is a microscopic single-celled organism found in pond water. It has a cell membrane, a dense rounded nucleus and many small bubble¬like vacuoles in its cytoplasm. Amoeba constantly changes its shape and positions. Hence, it has no definite shape. It pushes out one or more finger-like projections, called pseudopodia or false feet for movement and capture of food. When it senses food, it pushes out pseudopodia around the food particles and engulfs it. The food becomes trapped in a food vacuole.

Various digestive juices secreted inside the food vacuole digest the ingested food. The digested food is absorbed be the cytoplasm to provide energy to the cell body. The undigested waste is expelled by the body through the vacuole.

Class 7 Science Chapter 2 Nutrition in Animals Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define the term ingestion.
Answer:
The process of talking food into the body is called ingestion.

Question 2.
What is the other name of food pipe?
Answer:
The other name of food pipe is Oesophagus.

Question 3.
What is the function of salivary glands?
Answer:
Salivary glands secrete saliva that helps in softening and lubricating the food. It also contains salivary amylase that digests starch into simple sugars.

Question 4.
What is the length of small intestine in humans?
Answer:
The length of small intestine in humans is 7.5 cm.

Question 5.
What is the role of rectum in human digestive system?
Answer:
The rectum helps to store undigested waste material until it is passed out through anus.

Question 6.
Name the various types of teeth.
Answer:
The various types of teeth are incisors, canines, premolars and molars.

Question 7.
What is rumen?
Answer:
It is the part of stomach of some animals like cow, buffaloes and other grass-eating animals that contain cellulose digesting bacteria.

Question 8.
What is cud?
Answer:
The partially digested food in the rumen of a ruminant animal is called cud.

Question 9.
Where is the water from undigested food absorbed in the body?
Answer:
It is absorbed in the large intestine.

Question 10.
What are the different organs of alimentary canal?
Answer:
The different organs of the alimentary canal are mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Question 11.
What is digestion?
Answer:
The process in which complex food materials are broken into simpler and absorbable substances is called digestion.

Question 12.
What is the function of digestive juices?
Answer:
The digestive juices convert complex substances of food into simpler, soluble and absorbable forms.

Question 13.
What is the role of incisors?
Answer:
The incisors are used for biting and cutting the food.

Question 14.
What is absorption?
Answer:
After the food molecules become small, they pass through the walls of intestine and go into blood. This process is called absorption.

Question 15.
Name the five stages of the animal nutrition.
Answer:

Ingestion,
Digestion,
Absorption,
Assimilation,
Egestion.

Question 16.
Where does the process of digestion start and where does it end?
Answer:
The digestion starts from the mouth and is completed in the small intestine.

Question 17.
Name the juice secreted by the salivary glands.
Answer:
The juice secreted by the salivary glands is saliva.

Question 18.
What is the function of large intestine?
Answer:
Large intestine absorbs water from the undigested food material.

Question 19.
What is the function of oesophagus?
Answer:
The walls of oesophagus pushes the food from mouth towards the stomach.

Question 20.
What the pseudopodia?
Answer:
The body of amoeba has finger-like projections which are called pseudopodia.

Question 21.
Where is the pancreas located?
Answer:
Pancreas is located just below the stomach in the abdomen.

Short Answer Type Questions

Question 1.
State the various types of teeth and their function in human body.
Answer:
There are four kinds of teeth in human beings. Incisors are four in number in each jaw and help to cut and bite the food. Canines are two in number in each jaw and help to piercing and tearing the food. Premolars are four in number in each jaw and help in chewing and grinding the food. Molars are six in number in each jaw and also help in chewing and grinding the food like premolars.

Question 2.
What is rumination? Explain.
Answer:
The grass-eating animals like cow, buffalo, etc., chew continuously even when they are not eating grass. They store the eaten grass in a separate part of the stomach. The is part is called rumen. Here the food gets partially digested to form cud. Later, the cud returns to the mouth and animals chew it. This process is called rumination and the animals are called ruminants.

Question 3.
What is tongue? Write its function.
Answer:
Tongue is a muscular organ in our mouth. It helps in mixing the chewed food with saliva and swallowing the food. The tongue senses various tastes in the food as it has sense organs called the taste buds.

Question 4.
What is the unique feature of stomach?
Answer:
The stomach is a large organ which expands when food enters into it. The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices. Also, they secrete mucous and hydrochloric acid. The acid kills bacteria and the mucous protects the stomach lining from the action of acid.

Question 5.
Differentiate between absorption and assimilation?
Answer:

Absorption	Assimilation
1. The uptake of the digested food into the blood vessels is called absorption.	1. The process in which the absorbed food is used for producing energy and growth is called assimilation.

Question 6.
What does the gastric juice help to digest?
Answer:
The stomach secretes a digestive juice called gastric juice and hydrochloric acid. Protein present in the food is digested by the gastric juice.

Question 7.
What is cellulose?
Answer:
It is a type of complex carbohydrate. Many animals, including humans, cannot digest cellulose. The rumen in ruminants contain cellulose digesting bacteria.

Question 8.
What is the role of hydrochloric acid in human digestive system?
Answer:
Hydrochloric acid secreted inside the stomach makes the medium acidic for digestion of proteins by the gastric juices. Hydrochloric acid also causes disinfection of the food by killing the germs and bacteria.

Question 9.
How does the small intestine work in digestion of food in humans?
Answer:
The food in the small intestine is mixed with the bile juice from the liver and the pancreatic juice from the small intestine. While bile helps in the digestion of fats, pancreatic juice helps in the digestion of carbohydrates, proteins and fats. Intestinal juices from the small intestine are also mixed with the food and help in completing the process of digestion.

Question 10.
What happens when we do not clean our teeth after eating the food?
Answer:
If we do not clean our teeth after eating the food, then various harmful bacteria begin to live and grow on the food trapped in the teeth. These bacteria breakdown the sugar present in the food into acids and remain attached with teeth. The acid formed gradually damages the teeth. This is called tooth decay. This will eventually lead to pain or even loss of teeth.

Question 11.
At times, we feel burning sensation in our throat due to indigestion. Give the possible reason.
Answer:
It is due to the excessive spicy food we eat. When more amount of HCl is released by the stomach to digest the spicy food, then the mucus present in our stomach is not able to neutralise the effect of HCl. This sometimes gives rise to a burning sensation in our throat due to indigestion.

Question 12.
It is said that, ‘small intestine the site of the complete digestion’. Why it so?
Answer:
The small intestine receives the secretions of the liver and pancreas which help in the complete digestion of carbohydrates, proteins and fats. Hence, the digestion of food is completed here.

Long Answer Type Questions

Question 1.
Briefly explain the process of digestion in ruminants.
Answer:
Many animals including humans cannot digest cellulose. But ruminants can digest it. Ruminants include animals like cows, buffaloes and other grass-eating animals. These animals quickly swallow the grass and store it in a separate part of the stomach called rumen. The rumen contains cellulose digesting bacteria. The bacteria present in the rumen of the animal start to digest cellulose carbohydrate present in the grass food. Thus, the grass is partially digested in the rumen. The partially digested food in the rumen of the animals is called cud. After some time, the cud of the rumen returns to the mouth in small lumps and the animals chew it. This process is called rumination.

Question 2.
What is dental plaque? What harm can it do? How can the formation of plaque be prevented.
Answer:
If the teeth are not cleaned regularly, they become covered with a sticky, yellow layer of food particles and bacterial cells called dental plaque. Since plaque covers the teeth forming a layer over them, the alkaline salts cannot reach the tooth surface to neutralise the acid formed by the bacteria and hence tooth decay sets in. Brushing the teeth regularly after eating food, removes the plaque before bacteria produce acid. This will prevent tooth decay.

Question 3.
Explain the digestion in Amoeba.
Answer:
Amoeba is a microscopic organism and eats tiny plants and animals which float in water in which it lives. The mode of nutrition in amoeba is holozoic. The process of obtaining food by Amoeba is called phagocytosis. When it senses food in its surroundings, it projects various pseudopodia around it and engulf the food particle inside the food vacuole. Digestive juices digest the food inside the vacuole which is then absorbed be the cell cytoplasm. The waste is expelled out of the body by the vacuole.

Question 4.
Explain the human digestive system with the help of a labelled diagram?
Answer:
The human digestive system comprises of a group of organs and associated glands that work together in converting food into energy and other basic nutrients to obtain power for the body. The process of digestion starts from mouth and ends at anus. Alimentary canal is a long, muscular and coiled tube.

There are different organs in alimentary canal: mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus. When we take food in our mouth, salivary glands of mouth secrete saliva which moistens the food and digests starch. The tongue helps in chewing the food. From the mouth, food goes into the food pipe called oesophagus.

The food we eat is pushed down the oesophagus to the stomach by peristaltic movements. In the stomach, the food is churned and converted into a semi-solid paste. The stomach secretes a digestive juice called gastric juice that digests proteins. Then the food goes into the small intestine where the food is mixed with bile juice and pancreatic juice. These juices are important for digestion of fats, carbohydrates and proteins.

The undigested food moves from the small intestine to the large intestine where mainly absorption of water from the undigested food takes place. From the large intestine, the undigested food passes to the rectum which pushes it out of the body through the opening called anus.

Picture-Based Questions

Question 1.
Draw a diagram of tongue and label the regions of salt, bitter, sweet and sour sensations on it.
Answer:

Question 2.
Draw a diagram of arrangement of teeth in the buccal cavity of human beings and label the various types of teeth.
Answer:

Question 3.
a. Label the marks 1 and 2 shown in the diagram of digestive system of the ruminant animal given below.

b. Name the partially digested food in the rumen.
Answer:
a. 1. Rumen 2. Stomach
b. Partially digestive food in rumen is called cud.