Question:
Give reasons for the following.
- Fresh milk is boiled before consumption while processed milk is stored in packets and can be consumed without boiling.
- Raw vegetables and fruits are kept in refrigerators, whereas jams and pickles can be kept outside.
- Farmers prefer to grow beans and peas in nitrogen deficient soils.
- Mosquitoes can be controlled by preventing stagnation of water though they do not live in water. Why?
Solution:
- Fresh milk is boiled before consumption to kill the micro organisms that could be present in it. But packed milk is pasteurised and boiled at 70°C for 30 sec followed by sudden : chilling then stored.
Thus, it can be consumed without boiling. Pasteurisation kill all micro organisms for making it free of any contamination. - Raw vegetables and fruits get easily infected by micro organisms and get spoiled. They are kept in refrigerator at low temperature that inhibits growth of microbes. Jams and pickles contain sugar and salt as preservatives.
These preservatives forms a protective layer and prevent spoilage of these products by inhibiting the growth of various micro organisms. - Beans and peas are leguminous plants as they have Rhizobium, a bacteria in their root nodules. This bacteria can fix atmospheric nitrogen to enrich the soil with nitrogen and increase its fertility.
Farmers grow leguminous plants in between the major crops, a practice called crop rotation to restore the used nutrients of the soil. - Though mosquitoes, live on land, water is their breeding ground their larvae grow in water. Water stagnation is collecting of water in a small area, without any activity. Mosquitoes lay egg on such a surface.
If water stagnation is prevented, their larvae cannot survive, thus reducing mosquito population.