Food is required by all living beings to survive. The food contains various nutrients. The process by which the food is obtained and considered by a living organism to get energy and various other materials for the growth, repair, development and maintenance of the various body parts is called nutrition.
Modes or Types of Nutrition:
There are two modes of nutrition which are as under-
The mode of nutrition in which green plants prepare their own food with the help of sunlight trapped by chlorophyll is called autotrophic nutrition.
They use CO2 and H2O and manufacture carbohydrates in the presence of sunlight.
The process involves is called photosynthesis.
Such organisms are called autotrophs and their mode of nutrition is called autotrophic.
In this type of nutrition, the organism obtain organic food materials by consuming bodies or products of other living or dead plants or animals.
Heterotrophs can be classified into the following types depending on their feeding habits –
Herbivores – Animals that feed on plants are called herbivores. Example – deer, cow, rabbit, sheep, elephant, giraffe etc.
Carnivores – Animals that feed on the flesh of other animals are called carnivore. Example – lion, tiger, hyena, lizard etc. Some plants are also carnivores. Insects & small animals are digested with the help of digestive juices secreted by the cells of these plants. Sundew, venus flytrap & pitcher plant are some carnivorous (insectivorous) plants.
Omnivores – Animals that feed on both plants & flesh are called omnivores. Example – Human beings, dog, cockroach etc.
Parasites – Organisms that depend on other organisms for food & shelter are called parasites. The other organism is called the host. The parasite derives benefit from the host & harms it in the process. For example – roundworm & tapeworm are parasites living in the human intestine. Similarly, dodder is a parasitic plant that absorbs food material from host plants.
Saprophytes – Organisms that feed on dead & decaying organic matter are called saprophytes. Example – mushroom, earthworm & some bacteria.
Scavengers – Animals that feed on dead animals are called scavengers. Example – vulture, jackal, crow etc.
All heterotrophs depend on autotrophs directly or indirectly for food. Autotrophs in turn depend on sun for preparing food. Thus, all living organisms ultimately depend on sun for obtaining nourishment. Thus, sun is the ultimate source of energy on the earth.
Nutrition in Animals:
The various steps involved in the process of nutrition are as follows –
Ingestion – Ingestion is the process of taking in of food. Several animals have special organs for the process of ingestion.
Digestion – Digestion is the process of breaking down complex food molecules like carbohydrates & fats into simpler forms. Digestion is carried out with the help of certain chemical substances called enzymes. Enzymes are molecule made of protein that speed up chemical reactions in the body.
Absorption – It is the process by which digested food molecules are taken up (or absorbed) by the wall of the intestine & sent to the circulatory system (mainly blood). The circulatory system then transports the nutrients to different parts of the body. Thus the cells of the body absorb the digested food molecules.
Assimilation – It is the process of using the absorbed food molecules for deriving energy & for growth.
Egestion – It is the process by which undigested food is thrown out of the body.