Carbohydrates are the main constituents of most of the vegetation. While stems and branches of the plants and trees contain cellulose, seeds and fruits are storehouses of starch and glucose respectively. Thus all three substances — cellulose, starch and glucose — are carbohydrates.
Plants of pulses and beans of legumes as they are also called, are different from the plants of other vegetables and fruits. The roots of pulses and beans bear nodules in which a kind of bacteria known as ‘Rhizobium’ thrives. There is a close relationship of interdependence known as ‘symbiosis’ between the plants of pulses and these bacteria. Colonies of Rhizobium bacteria get sustenance from the roots of pulses and beans plants and provide nutritious fertilizer to the host plants in return. They do this by a process called ‘nitrogen fixing’, i.e. converting nitrogen in the atmosphere into nutritious fertilizer which can be assimilated by the plants. The plants of pulses and beans process the nitrogen provided by Rhizobium bacteria into amino acid and thereafter convert it into protein.