Question

Give reasons for the following. 

(a) Fresh milk is boiled before consumption while processed milk stored in packets can be consumed without boiling. 

(b) Raw vegetables and fruits are kept in refrigerators whereas jams and pickles can be kept outside. 

(c) Farmers prefer to grow beans and peas in nitrogen deficient soils. 

(d) Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?

Answer 1

(a) Fresh milk is boiled before consumption to kill the microorganisms in it. But packed milk is pasteurised and does not contain any microorganisms. It can thus be consumed without boiling. 

(b) Raw vegetables and fruits get easily infected by microorganisms and get spoilt. They are kept in refrigerator as low temperature inhibits growth of microbes. Jams and pickles contain sugar and salt as preservatives. They do not get infected by microbes easily. 

(c) Beans and peas are leguminous plants and have Rhizobium in their root nodules. These bacteria can fix atmospheric nitrogen to enrich the soil with nitrogen and increase its fertility. 

(d) Though mosquitoes live on land, their larvae grow in water. If water stagnation is prevented the larvae cannot survive.