Biology Class 12 NCERT Solutions: Chapter 10 Microbes in Human Welfare Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

Get top class preparation for CBSE/Class-12 right from your home: get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-12.

Q. 14 Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd


  • The order of arrangement of products according to their decreasing importance is:

Penicillin-Biogas − Citric acid − Curd

  • Penicillin is the most important product for the welfare of human society. It is an antibiotic, which is used for controlling various bacterial diseases.
  • The second most important product is biogas. It is an eco-friendly source of energy. The next important product is citric acid, which is used as a food preservative.
  • The least important product is curd, a food item obtained by the action of lactobacillus bacteria on milk.
  • Hence, the products in the decreasing order of their importance are as follows: Penicillin-Biogas − Citric acid − Curd

Q. 15 How do biofertilisers enrich the fertility of the soil?


  • Bio-fertilizers are living organisms which help in increasing the fertility of soil. It involves the selection of beneficial micro-organisms that help in improving plant growth through the supply of plant nutrients.
  • These are introduced to seeds, roots, or soil to mobilize the availability of nutrients by their biological activity.
  • Thus, they are extremely beneficial in enriching the soil with organic nutrients. Many species of bacteria and cyanobacteria have the ability to fix free atmospheric nitrogen.
  • Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants.
  • Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabaena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria.
  • Biofertilisers are cost effective and eco-friendly.
Fertility of Soil

Developed by: