Microbes in Human Welfare — BIOLOGY STD 12 Science — Question

Lactic Acid Bacteria (LAB) sets milk into curd and also plays a very beneficial role for human health. Give any two suitable reasons.

Name and explain the mechanism by which seeds from hybrid plants are developed that are able to retain the desired hybrid character in the progeny.

How does 'fitness' of a population help in evolution?

1. What precaution(s) would you recommend to a patient requiring repeated blood transfusion?
2. If the advise is not followed by the patient there is an apprehension that the patient might contract a disease that would destroy the immune system of his/her body.

Explain with the help of schematic diagram only how the immune system would get affected and destroyed.

Explain briefly how the principle of natural selection can be applied to the development of resistance in mosquitoes for DDT.

How would you find genotype of a tall pea plant bearing white flowers? Explain with the help of a cross. Name the type of cross you would use.

Two independent monohybrid crosses were carried out involving a tall pea plant with a dwarf pea plant. In the first cross, the offspring population had equal number of tall and dwarf plants, whereas in the second cross it was different. Work out the crosses, and explain giving reasons for the difference in the offspring populations.

OR

Work out a cross to find the genotype of a tall pea plant. Name the type of cross.

What do you mean by in-situ and ex-situ conservation of wildlife?

The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give reasons.

Explain the types of Natural Birth Control Method.