Q4. Find out the role of microbes in (a) single cell protein (SCP) and (b) the soil. (NCERT Exercise 13, page 160.)
(a) Beyond the NCERT text: single cell protein (SCP) is protein made by growing microbes, such as bacteria, yeasts and other fungi, or algae, in bulk, for use as food or animal feed (Wikipedia, “Single-cell protein”, facts in our words). (b) In the soil, microbes act as biofertilisers: nitrogen-fixing bacteria and cyanobacteria add nitrogen, mycorrhizal fungi pass phosphorus to plants, and cyanobacteria add organic matter (NCERT page 158); fungi such as Trichoderma in root ecosystems also control plant pathogens (NCERT Section 8.5, page 157).
Q5. Why is there pressure to switch from chemical fertilisers to biofertilisers?
The use of chemical fertilisers to meet the ever-increasing demand for agricultural produce has contributed significantly to environmental pollution, and overusing them causes problems (NCERT pages 157–158).
Q6. Into what form does Rhizobium fix atmospheric nitrogen, and who uses it?
Into organic forms, which the leguminous plant uses as nutrient (NCERT page 158).
Q7. Which genus forms mycorrhiza in many plants, according to NCERT?
Glomus (NCERT page 158).
Q8. Why are cyanobacteria valued in paddy fields?
In paddy fields cyanobacteria serve as an important biofertiliser: many fix atmospheric nitrogen, and they also add organic matter to the soil and increase its fertility (NCERT page 158).