- The materials which provide the two primary requirements of life, namely, energy and raw materials, are called nutrients.
- A substance which is taken to supply the necessary nutrients to the body is termed food, or diet.
- The sum total of the processes by which the living organisms obtain food and utilize it for use in various biological activities such as growth, maintenance and for meeting their energy needs is termed as nutrition.
TYPES OF NUTRITION
The organisms have evolved two different types of nutrition: autotrophic, heterotrophic
1. Autotrophic Nutrition or Holophytic Nutrition
- Preparation of organic food from the inorganic materials in the organism’s own body is called autotrophic nutrition. (autos = self, troph = nourishment)
Autotrophic nutrition is of two types: photoautotrophic and chemoautotrophic.
A. Photoautotrophic: Preparation of organic food from the inorganic materials in the organism’s own body by utilizing the energy of the sun is called photoautotrophic nutrition.
For example: All green plants, certain protists (Euglena viridis) and some bacteria (green Sulphur bacterium, Chlorobium)
- They take carbon dioxide and water from the environment and transform these into glucose and oxygen with the help of the sun’s energy trapped by chlorophyll.
- This process of making organic food with the help of sunlight is called photosynthesis.
The process of photosynthesis is briefly represented by the following equation
6 CO2 + 6 H2O → C6H1206 + 602
Carbon dioxide water glucose oxygen
- The organisms capable of photosynthesis are termed phototrophs.
- They retain glucose to prepare other organic materials from it, and release oxygen as a byproduct.
B. Chemoautotrophic Nutrition
- Some bacteria capture energy released during oxidation of inorganic chemical substances and prepare organic food with its help.
- They are known as chemotrophs.
- The process of preparing organic food with the help of energy from chemical reactions is known as chemosynthesis.
- For example: Nitrifying bacteria Nitrosomonas and Nitrobacter are chemotrophs.
- Since both phototrophs and chemotrophs do not take organic molecules produced by other organisms, they are called autotrophs or “self-nourishing.”
2. Heterotrophic Nutrition
- Taking organic food synthesized by autotrophs is termed heterotrophic nutrition.
- The organisms which take ready-made organic food are called heterotrophs.
- They get organic molecules by taking plants or animals (living or dead) or their products, and obtain energy by “burning” these molecules in their body.
Heterotrophic mode of nutrition is of three types:
A. Saprotrophic nutrition: in which an organism obtains its food from decaying organic matter of dead plants, dead animals and rotten bread, etc.
B. Parasitic nutrition:
- The parasitic nutrition is that nutrition in which an organism derives its food from the body of another living organism (called its host) without killing it.
- The organism which obtains the food is called a ‘parasite’ and the organism from whose body food is obtained is called the ‘host’.
- For example: Plasmodium’ (which causes malaria disease) is a parasite. Roundworm which causes diseases in man and domestic animals is also a parasite.
C. Holozoic nutrition:
- in which an organism takes the complex organic food materials into its body by the process of ingestion, the ingested food is digested and then absorbed into the body cells of the organism.
- For example: words, man, cat, dog, cattle, deer, tiger, lion, bear, giraffe, frog, fish and Amoeba, etc., have the holozoic mode of nutrition