Evolution — BIOLOGY STD 12 Science — Question

Define the following terms and give one example for each .

Give any three salient features of the double helix structure of DNA.

Write a short note on lactation.

Males in whom testes fail to descend to the scrotum are generally infertile. Why ?

What do you understand by balance of an ecosystem.

Name and mention the events that occur in the cells when HIV gets into blood after gaining entry into the human body.

A culture plate of Lactobacillus shows blue-coloured colonies and colourless colonies. Explain the principle involved in the formation of such variance in the colour of colonies.

How does addition of a small amount of curd to fresh milk help in the formation of curd? Mention a nutritional quality that gets added to the curd.

OR

How does ‘starter’ added to milk help it to set into curd?

Explain: Multiple allelism