Nutrition in Animals-Class 7-Science-NCERT solutions
NCERT notes alongwith solutions for class 7 science “Nutrition in Animals” are provided here. The notes as well as solutions are very much helpful for the students to understand the topics. The solutions will be handy for quickly completing the homework and preparing for exams.
In earlier chapter 1 “Nutrition in Plants“, we have learnt that Plants are autotrophs which means that plants can prepare their own food. But, in this chapter (Nutrition in Animals) we will learn about “how animals get their nutrition from the food which they eat. Animals are heterotrophs which means animals depend upon others for their food. Animals get their food from plants, either directly by eating plants or indirectly by eating plants eating animals.
Different Ways of Taking Food
The mode of taking food into the body varies from organism to organism such as:
- Bees and humming-birds suck the nectar of plants
- Infants of humans and many other animals feed on mother’s milk.
- Snakes like the python swallow the animals they prey upon.
- Some aquatic animals filter tiny food particles floating nearby and feed upon them.
What is digestion?
Digestion is the process by which our body breaks down complex food into smaller and simpler substances so that it can be absorbed and used for energy, growth and repair.
Digestion in Humans
Human beings show a holozoic mode of nutrition which involves basically five basic steps.
- Ingestion: The process of taking food into the body is called ingestion.
- Digestion: the process by which our body breaks down complex food into smaller and simpler substances so that it can be absorbed and used for energy, growth and repair.
- Absorption: It is the process in which all the digested food is absorbed by the walls of the intestines.
- Assimilation: It is the process in which the absorbed food is transported to every cell of the body where they are used to produce energy.
- Egestion: It is the process in which the undigested food/ waste is excreted out from the body.
Let`s know what happens to the food in our body.
- When we eat food. The food passes through a continuous canal, also called alimentary canal or digestive tract, which begins at the buccal cavity and ends at the anus.
- The alimentary canal can be divided into six (06) compartments: (1) the buccal cavity, (2) food pipe or oesophagus (3) stomach, (4) small intestine, (5) large intestine ending in the rectum and (6) the anus.
These six parts together form the alimentary canal, also called digestive tract.
- The food components gradually get digested as food travels through these compartments.
- The inner walls of the stomach and the small intestine, and the various glands associated with the canal such as salivary glands, the liver and the pancreas secrete digestive juices.
- The digestive juices convert complex substances of food into simpler ones. The digestive tract and the associated glands together constitute the digestive system.
Digestion of food in different parts of the digestive tract
1. The mouth and buccal cavity
- Food is taken into the body through the mouth. We chew the food with the teeth and break it down mechanically into small pieces.
- Human Teeth – Each tooth in the human mouth is rooted in a separate socket. These sockets are known as “Gums”. In human beings, there are four types of teeth – Incisor, Canine, Premolar and Molar.
Human Tongue
- The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. It is free at the front and can be moved in all directions.
- We use our tongue for talking. Besides, it mixes saliva with the food during chewing and helps in swallowing food.
- We also taste food with our tongue. It has taste buds that detect different tastes of food. Regions of the tongue for different tastes are shown in the picture given below:
2. The foodpipe or Esophagus
- The swallowed food passes into the foodpipe or oesophagus. It is a muscular tube that connects throat to stomach.
- Food is pushed down by movement of the wall of the foodpipe. Actually this movement takes place throughout the alimentary canal and pushes the food downwards.
3. The stomach
- The stomach is a thick-walled bag. Its shape is like a flattened J and it is the widest part of the alimentary canal.
- It receives food from the food pipe at one end and opens into the small intestine at the other.
- The inner lining of the stomach secretes mucous, hydrochloric acid (HCl) and digestive juices. The mucous protects the lining of the stomach. The hydrochloric acid (HCl) kills many bacteria that enter along with the food and makes the medium in the stomach acidic and helps the digestive juices to act.
- The digestive juices break down the proteins into simpler substances.
4. The small intestine
- The small intestine is highly coiled and is about 7.5 metres long.
- It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices.
- Liver – The liver is a reddish brown gland situated in the upper part of the abdomen on the right side. It is the largest gland in the body. It secretes bile juice that is stored in a sac called the gall bladder. The bile plays an important role in the digestion of fats.
- Pancreas – The pancreas is a large cream-coloured gland located just below the stomach. The pancreatic juice acts on carbohydrates, fats and proteins and changes them into simpler forms.
- The partly digested food now reaches the lower part of the small intestine where the intestinal juice completes the digestion of all components of the food.
- The carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and proteins into amino acids.
Absorption in the small intestine
- The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi.
- Each villus has a network of thin and small blood vessels close to its surface. The surface of the villi absorbs the digested food materials.
- The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the body. This is called assimilation.
- In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water, and energy is released. The food that remains undigested and unabsorbed enters into the large intestine.
5. Large intestine
- The large intestine is wider and shorter than the small intestine. It is about 1.5 metre in length.
- Its function is to absorb water and some salts from the undigested food material.
- The remaining waste passes into the rectum and remains there as semi-solid faeces. The faecal matter is removed through the anus from time-to-time. This is called egestion.
Digestion in grass eating animals
- Cow, Goats, Buffaloes and other grass eating animals quickly swallow the grass and store it in a part of stomach called rumen. Rumen possesses cellulose digesting bacteria which breakdown the food by fermentation. This partially digested food or grass present in the rumen of cow is called cud.
- This cud is brought back into the mouth of the cow from the rumen into small lumps and animal chews it again. This process is called rumination and animals are called ruminants.
- When this cud is thoroughly chewed in the mouth of the cow, it is swallowed again. This time the chewed cud does not go back to rumen but enter into the other compartments of cow’s stomach and then into the small intestine for complete digestion and absorption of food.
Feeding and Digestion in Amoeba
- Amoeba is a microscopic single-celled organism found in pond water.
- Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles in its cytoplasm.
- Amoeba constantly changes its shape and position. 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 particle and engulfs it.
- The food becomes trapped in a food vacuole. Digestive juices are secreted into the food vacuole. They act on the food and break it down into simpler substances. Gradually the digested food is absorbed.
Activity 1: List all the components of food
Sol:
- Carbohydrates
- Fats
- Proteins
- Vitamins
- Minerals
Activity 2.1 Type of food and mode of feeding of the following animals
Activity: 2.2 (Human Teeth)
Solution of the exercise
1. Fill in the blanks
(a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________.
(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 outgrowths called _________.
(e) Amoeba digests its food in the ____________
Solution:
(a) ingestion, digestion, absorption, assimilation, egestion
(b) Liver
(c) digestive
(d) Villi
(e) food vacuole.
2. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Digestion of starch starts in the stomach. (T/F)
(b) The tongue helps in mixing food with saliva. (T/F)
(c) The gall bladder temporarily stores bile. (T/F)
(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F)
Solution:
(a) False. (The digestion of starch begins in the mouth. The salivary gland present in the mouth releases saliva which mixes and moistens the food that we eat. The saliva also contains an enzyme called “Salivary Amylase” which breaks down the starch into simpler ones.)
(b) True.
(c) True
(d) True
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
(b) Water from the undigested food is absorbed mainly in the
(i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine
Solution:
(a) (iii) small intestine
(b) (iv) large intestine
4. Match the items of Column I with those given in Column II:
5. What are villi? What is their location and function?
Sol:
Villi are small finger-like outgrowths that originate from the inner walls of the small intestine. Villi are located in the inner walls of the small intestine. Its main function is to increase the surface area of the small intestine and facilitate the absorption of nutrients from the digested food into the bloodstream.
6. Where is the bile produced? Which component of the food does it help to digest?
Sol:
Bile juice is produced in the liver and stored in a sac called gall bladder. It plays a key role in the digestion of fats in the small intestine.
7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Sol:
Cellulose, a type of carbohydrate, that ruminants can digest but not by humans. Ruminants like-horses, rabbits etc. have a large sac-like structure called Caecum between the Oesophagus and the small intestine. The cellulose of the food is digested here by the action of certain bacteria which are not present in humans. Due to the absence of such bacteria, humans cannot digest cellulose.
8. Why do we get instant energy from glucose?
Sol:
Glucose is a simple sugar. When we consume glucose, it breaks down with the help of oxygen in the cells and gives instant energy to the body. Glucose does not need digestion, it is directly absorbed into the blood.
9. Which part of the digestive canal is involved in:
(i) absorption of food ________________.
(ii) chewing of food ________________.
(iii) killing of bacteria ________________.
(iv) complete digestion of food ________________.
(v) formation of faeces ________________.
Sol:
(i) small intestine
(ii) mouth/ buccal cavity
(iii) stomach
(iv) small intestine
(v) large intestine
10. Write one similarity and one difference between the nutrition in amoeba and human beings.
Sol:
Similarity- (i) Both amoeba and humans have the same basic process of digestion of food and release of energy. They both secrete digestive juices that act on food and break it into simpler substances.
Differences- (i) Amoeba engulfs its food by surrounding the food particle with its pseudopodia whereas humans take the food inside its mouth with the help of its hand.
(ii) In amoeba, the digestive juices are secreted in the food vacuole whereas in humans digestive juices are secreted in the buccal cavity, stomach and small intestine.
11. Match the items of Column I with suitable items in Column II
The solution of the match the items of Column I with Column II
12. Label Fig. 2.11 of the digestive system.
Solution: The picture of the digestive system after labelling is shown below.
13. Can we survive only on raw, leafy vegetables/grass? Discuss
Sol:
No, we cannot survive only on raw, leafy vegetables/ grass. The reason is that the grass is rich in cellulose, a type of carbohydrate. Humans cannot digest cellulose because certain types of bacteria and enzymes are absent in their digestive organs.