Functions of food
1. It provides energy to do work.
2. It provides raw materials necessary for growth, development, reproduction and for the synthesis of variety of substances in the body.
3. It helps in repairing damaged cells and tissues.
Modes of Nutrition:
1. Autotrophic Nutrition: In this type of nutrition organisms makes its food itself by the process of photosynthesis. The organism takes CO2 and H2O from the environment and in the presence of chlorophyll and sunlight makes its food in the form of carbohydrates (Glucose). It is the source of energy to the plants. Excess glucose is stored in the form of starch.
CO2 +H2O Chlorophyll C6H12O6 +6O2
Heterotrophic Nutrition: It is the type Nutrition in which organisms can not make its own food directly and indirectly.
Types of heterotrophic nutrition:
1. Holozoic Nutrition: The animals engulf the food material which is a complex molecule and is broken down into simpler substances. It involves ingestion, digestion, absorption of digested food and egestion e.g. animals
2. Saprophytic Nutrition: The organisms feed on dead and decaying matter like fungi, molds, yeast, and mushroom. The enzymes are released outside the body from the dead organic matter. Enzymes break the complex organic matter into simple substances. Soluble forms of this substance are then absorbed by the organisms.
3. Parasitic Nutrition: When an organism takes its food from other living organisms without killing them. The organism is called parasite and from whom the food is taken is called host. The parasites live on or inside the body of their host e.g. round worm, tapeworm, ticks cuscuta etc.