Nutrition in animal

In the previous chapter, we have learnt that green plants can make their own food by the process of photosynthesis. Unlike green plants, animals cannot prepare their own food, they depend on plants for their food directly or indirectly.

We know that all organisms including humans need food for growth, for repairing damaged parts of their bodies and for obtaining energy to carry out life processes. Animal nutrition is a process of taking food by an organism and its digestion, absorption and utilisation in the body.

DIFFERENT STEPS IN THE PROCESS OF NUTRITION

There are five main steps in the process of nutrition in animals. These are ingestion, digestion, absorption, assimilation and egestion.

1. Ingestion

The process by which the food is taken inside the body of an organism is called ingestion. When we put food into our mouth with hands, we are ingesting the food. However, different animals ingest food in different ways and have special organs for this purpose.

2. Digestion

The food of most animals consists of complex, insoluble substances that cannot be absorbed by their body. The breakdown of complex, insoluble food substances into simple, soluble food substances with the help of digestive juices prepared by the body is called digestion.

3. Absorption

The process in which the simple, soluble digested food substances are absorbed into the blood is called absorption.

4. Assimilation

The simple, soluble absorbed food substances are transported to the different parts of the body where they are utilised for energy, growth and repair. This process is called assimilation.

5. Egestion

A part of the food that we eat, remains undigested and unabsorbed. It cannot be utilised by the body. The process in which the undigested food is removed from the body is called egestion.

MODES OF PROCURING FOOD

The mode of procuring food into the body varies in different organisms. Each organism has some special structure to procure food.

1. Human beings: Human beings use their hands to take food into their mouth.

2. Ruminants: Ruminating animals, such as cow and horse, pick up food directly by their mouth.

3. Paramecium: Paramecium (unicellular organism) has fine hair-like structures called cilia all over its body (Fig. 2.1). The constant movement of