 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 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 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 INGRASS-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 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.





 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.