NCERT Gist: Nutrition in Animals | Additional Study Material for UPSC PDF Download

- Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
- The components of food such as carbohydrates are complex substances.
- These complex substances cannot be utilised as such.
- So they are broken down into simpler substances.
- The breakdown of complex components of food into simpler substances is called digestion.
- Starfish feeds on animals covered by hard shells of calcium carbonate.

Digestion in Humans

- The food passes through a continuous canal which begins at the buccal cavity and ends at the anus.
- The canal can be divided into various compartments: (1) the buccal cavity, (2) food pipe oesophagus, (3) stomach, (4) small intestine , (5) large intestine ending in the rectum rectum and (6) the anus.
- These parts together form the alimentary canal (digestive tract). The digestive tract and the associated glands together constitute the digestive system.
- The saliva breaks down the starch into sugars.
- The swallowed food passes into the food pipe or oesophagus.
- The stomach-widest part of the alimentary canal.
- 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.
- The digestive juices break down the proteins into simpler substances
- 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.
- 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.
- 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.
- The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption.
- The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi (singular villus).
- Large intestine is wider and shorter than small intestine.
- 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

- Actually, they quickly swallow the grass and store it in a separate part of the stomach called rumen.

Diarrhoea

- Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhoea.
- Caused by an infection, food poisoning or indigestion.
- Very common in India, particularly among children.
- Under severe conditions it can be fatal because of the excessive loss of water and salts from the body.
- Diarrhoea should not be neglected.
- Even before a doctor is consulted the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS).
- Food partially digested and is called cud.
- 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.
- The grass is rich in cellulose, a type of carbohydrate.
- Many animals, including humans, cannot digest cellulose.
- Ruminants have a large sac-like structure between the small intestine and large intestine.

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 bubblelike 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.
- Amoeba feeds on some microscopic organisms.
- 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.
- The absorbed substances are used for growth, maintenance and multiplication.
- The undigested residue of the food is expelled outside by the vacuole.
- The basic process of digestion of food and release of energy is the same in all animals.
- In a later chapter you will learn about the transport of food absorbed by the intestine to the various parts of the body.