[Short Notes – E&B] NCERT Class VII – Science – Nutrition in Animals – Chapter 2 – Part 2
[Short Notes – E&B] NCERT Class VII – Science – Nutrition in Animals – Chapter 2 – Part 1
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Read complete book (must) at : NCERT Class VII – Science – Nutrition in Animals – Chapter 2
The stomach
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The stomach is a thick-walled bag. Its shape is like a flattened U 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.
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The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices.
The mucous protects the lining of the stomach. The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic.
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The digestive juices break down the proteins proteins proteins proteins proteins into simpler substances.
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The small intestine
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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.
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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.
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The pancreas is a large cream coloured gland located just below the stomach.
The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms.
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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.
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Absorption in the small intestine
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The digested food can now pass into the blood vessels in the wall of the intestine.
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This process is called absorption.
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The inner walls of the small intestine have thousands of finger-like outgrowths.
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These are called villi (singular villus).
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The villi increase the surface area for absorption of the digested food.
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Each villus has a network of thin and small blood vessels close to its surface.
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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.
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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 then enters into the large intestine.
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Large intestine
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The large intestine is wider and shorter than small intestine.
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It is about 1.5 metre in length.
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Its function is to absorb water and some salts from the undigested food material.
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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.
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DIGESTION IN GRASS – EATING ANIMALS
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They quickly swallow the grass and store it in a separate part of the stomach called rumen.
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Here the food gets partially digested and is called cud.
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But later the cud returns to the mouth in small lumps and the animal chews it.
This process is called rumination and these animals are called ruminants.
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The grass is rich in cellulose, a type of carbohydrate.
Many animals, including humans, cannot digest cellulose.
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Ruminants have a large sac-like structure between the small intestine and large intestine.
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The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.
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FEEDING AND DIGESTION IN AMOEBA
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Amoeba is a microscopic single-celled organism found in pond water.
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It has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles in its cytoplasm.
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It constantly changes its shape and position.
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It pushes out one, or more finger-like projections, called pseudopodia or false feet for movement
and capture of food.
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Amoeba feeds on some microscopic organisms.
When it senses food, it pushes out pseudopodia around the food particle and engulfs it.
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The food becomes trapped in a food vacuole.
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Digestive juices are secreted into the food vacuole.
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They act on the food and break it down into simpler substances.
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Gradually the digested food is absorbed.
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The absorbed substances are used for growth, maintenance and multiplication.
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The undigested residue of the food is expelled outside by the vacuole.
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Chapter 3
