Give reasons for the following:                

Testes descend into the scrotum before birth.

Give reasons for the following:                                                                                                

Give reasons for the following:                                                                      
Nitrogenous fertilisers are not applied in fields where leguminous crops grow.

Give reasons for the following:  

Genetic code is ‘universal’.

Give reasons for the following:                                                                          

At higher temperatures, green plants start evolving CO₂ instead of O₂.                                          

State the best known contribution of:
(i) Alec Jeffery
(ii) P.K. Sethi
(iii) Hugo de Vries

17.

Expand the following :

(i) SCID

(ii) ZIFT

Describe the Miller and Urey experiment on the origin of life.

(b) Define the following:

(i) Frame shift mutations.
(ii) Genetic drift.

(a) Name and define the three types of natural selection.
(b) State the following:
(i) Hardy Weinberg’s principle
(ii) Theory of recapitulation