Class 12th Biology 2011 Set3 Delhi Board Paper Solution

(a) Biofertiliser is preferred over chemical fertilizer because:

1. Biofertiliser would be better in the long run because they contain organic materials while fertilisers contain chemical substances that when used in excess become harmful to the consumers.

2. Continuous application of fertilisers to the soil decreases its fertility and also leads to increase in the acidity of the soil.

3. Fertiliser runoff from the fields also causes water pollution.

(b) Anabaena and mycorrhiza acts as biofertiliser:

Fungi such as Glomus form symbiotic associations with plants. This relationship is known as Mycorrhiza. They absorb phosphorus from the soil and pass it to plants.

Cyanobacteria such as Anabaena and Nostoc also fix atmospheric nitrogen and act as bio-fertilizers especially in paddy fields.