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2 Nutrition in Animals
You have learnt in Chapter 1 that plants can prepare their own food by the process of photosynthesis but animals cannot. Animals get their food from plants, either directly by eating plants or indirectly by eating animals that eat plants. Some animals eat both plants and animals. Recall that all organisms including humans require food for growth, repair and functioning of the body. Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
You have studied in Class VI that food consists of many components. Try to recall and list them below:
The components of food such as carbohydrates are complex substances. These complex substances cannot be utilised as such. So they are brokendown into simpler substances. The breakdown of complex components of food into simpler substances is called digestion.
2.1 DIFFERENT WAYS OF TAKING FOOD
The mode of taking food into the body varies in different organisms. Bees and humming-birds suck the nectar of plants, infants of human and many other animals feed on mother’s milk. Snakes like the python swallow theanimals they prey upon. Some aquatic animals filter tiny food particles floating nearby and feed upon them.
2.2 DIGESTION IN HUMANS
We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. Have you ever wondered what happens to the food inside the body? The food passes through a continuous canal (Fig. 2.2) which begins at the buccal cavity and ends at the anus. The canal can be divided into various compartments: (1) the buccal cavity, (2) foodpipe or oesophagus, (3) stomach, (4) small intestine, (5) large intestine ending in the rectum and (6) the anus. Is it not a very long path? These parts together form the alimentary canal (digestive tract). The food components gradually get digested as food travels through the various compartments. The inner walls of the stomach and the small intestine, and the various glands 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. Now, let us know what happens tothe food in different parts of the digestive tract.
1. Fill in the blanks:
(a) The main steps of digestion 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 ____________ .
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 chewit for some time. (T/F)
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
5. What are villi? What is their location and function?
6. Where is the bile produced? Which component of the food does it digest?
7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
8. Why do we get instant energy from glucose?
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 ________________.
10. Write one similarity and one difference between the nutrition in amoeba and human beings.
Please refer to attached file for NCERT Class 7 Science Nutrition in Animals
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