number of steps using certain special intermediate compounds and enzymes. RUBP (Ribulose 1-5 bis Phosphate) is the compound which accepts CO2 in this process. Finally the glucose is converted to starch.

Plants are capable of surviving under a range of situations, from very hot, dry and brightly lighted conditions to wet, humid and dimly lighted ones. The requirement of light and other factors varies from one plant to another.

Heterotrophic Nutrition

In the living world all organisms are capable of surviving under different conditions and acquring their food in different ways. We have studied about organisms that can capture light to produce their food. These are autotrophic in nature. While those that can not are heterotrophic.

How do organisms obtain their nutrition

Depending on the type and availability of food organisms can assort to a range of strategies of food intake and use. Some organisms break down the food materials outside the body and then absorb it.

For example, bread moulds, yeast, mushrooms etc. which are called saprophytes. Some other organisms derive nutrition from plants or animals without killing them.

This type of parasitic nutritive strategy is used by a wide variety of organisms like Cuscuta, lice, leeches and tape worms. Others take in whole material and break it down inside their bodies. What can be taken in and broken down depends on the bodys’ design and it’s function. Sinc

e the food and the way it is obtained differs, the digestive system is also different in various organisms. In single celled organisms, like amoeba the food may be taken in by the entire surface but as the complexity of the organism increases, different parts become specialized to perform different functions.

For example amoeba [fig-9(a)]

takes in food using temporary finger like extensions (pseudopodia) of the cell surface which fuse over the food particle forming food vacuole.

Inside the food vacuole, complex substances are broken down into simpler ones. Then diffuse into the cytoplasm.

The remaining undigested material is moved to the surface of the cell and thrown out. In Paramoecium [fig-9(b)], which is also a unicellular organism the cell has a definite shape.

Food is taken in at a specific spot. Food is moved to the spot by the movement of cilia which covers the entire surface of the cell, where the food is ingested (cytostome).