Nutrition is the process of obtaining food and then using it for obtaining energy, growth and repair of the body. There are five main processes concerned with the use of food by animals. As we know that Plants produces their own food by the help of photosynthesis. But animals are heterotrophs and hence they depend on other organisms for their food. This readymade food comes either from plants or from other animals. We are also animals and obtain food from plants in the form of rice, pulses, vegetables etc. and foods like milk; eggs, chicken, fish etc are obtained from other animals. Many other animals obtain their f3
3ood by eating the flesh of other animals like fish, birds, snake etc. The big fish eat small fish, the snake eats frog and the insects eat dead bodies of animals. The non- green plants also obtain their food from other plants or animals e.g yeast plant. Also, plant eats insects like pitcher plant and Venus fly- trap.
Animals are divided in to three groups on the basis of their food habits. These are: Herbivores, Carnivores and Omnivores.
(i) Herbivores: are those animals which eat only plants like grasses, leaves, fruits etc. Examples of herbivores are: Goat, Cow, Sheep, Horse, Ox, Elephant etc. Thus, herbivores are plant eaters and also known as herbivorous animals.
(ii) Carnivores: are those animals which eat other animals as food or they eat meat or flesh of other animals. Examples are: Lion, Tiger, Frog, Vulture, Lizard etc.Therefore, Carnivores are meat eaters and known as carnivorous animals.
(iii) Omnivores: are those animals which eat both plants and animals. Examples are; Man (Human Beings), Dog, Crow, Bear, Ant etc. Thus, Omnivores are plant eaters as well as meat eaters and known as Omnivorous animals.
As we know all the living things depend on sun for their own food. Plants use the energy of sun and prepare food by photosynthesis. Plants are eaten by herbivores and omnivores as food. Meat eaters or carnivores also eat other animals or other carnivores in the form of food and scavengers eat dead and decaying plant and animal. So, it is the energy of sun which provides food for plants and animals.
There are five steps in the process of Nutrition in animals. These are: Ingestion, Digestion, Absorption, Assimilation and Egestion.
There are two very simple animals namely amoeba and paramecium. They are made up of single cell and so known as unicellular animals. So, all the 5 processes of nutrition are performed by single cell. The mode of nutrition in amoeba is holozoic. They eat tiny or microscopic plants and animals as food which floats in water in which it lives. The process of obtaining food by Amoeba is called phagocytosis means cell feeding.
(i) Ingestion: Amoeba has no mouth so food is ingested by using pseudopodia. When food comes near amoeba, then amoeba ingests this food particle by forming temporary finger like projections called pseudopodia around it. And the engulfed food with water formed a food vacuole which is considered as ‘ Temporary stomach’ of Amoeba.
(ii) Digestion: In Amoeba food is digested in the food vacuole by digestive enzymes. These enzymes break down the food in to small and soluble molecules by chemical reactions.
(iii) Absorption: The digested food present in the food vacuole of Amoeba is absorbed directly in to the cytoplasm by diffusion. Due to the presence of one cell, blood is not required to carry the digested food. The food just spreads out from the food vacuole in to the whole cell of Amoeba and finally food vacuole disappears.
(iv) Assimilation: A part of the absorbed food is used to obtain energy through respiration and the remaining part of the food leads to the growth in Amoeba. And then amoeba can reproduce by dividing in to two daughter cells.
(v) Egestion: Amoeba has no fixed place for removing the undigested part of food.When a considerable amount of undigested food collects inside amoeba, then its cell membrane suddenly ruptures at any place and undigested food is thrown out of the body of Amoeba.
In case of Paramecium, hair like structures called cilia helps to sweep the food particles from water and put them in to mouth. This step is known as ingestion which is followed by other steps such as digestion, absorption etc.
Nutrition in complex multicellular Animals like man, fish, frog etc. all the processes involved in nutrition are performed by a combination of digestive organs. And this combination of digestive organs is called Digestive System which we will be discussing in our next article in details.
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