Evolution — BIOLOGY STD 12 Science — Question

What is apomixis and what is its importance?

Explain the surgical method of contraception with the help of a labelled diagram.###Write the name of a surgical contraceptive method and explain it which can be adopted by the male member of the couple.

Vicky's mother was using the same mosquito repellent cream from last six years. She was regularly complaining that this cream has no effects on mosquitoes now. Hearing this, Vicky advised his mother to change the cream as regular usage has led the mosquitoes to develop resistance against it. His mother changed the cream and could notice its effect on mosquitoes.

1. Explain how mosquitoes were not affected by the previous cream?
2. On what factors, Darwin's theory was based?
3. Can you relate this incident to Darwin's concept? How?
4. Identify the values shown by Vicky.

Write the causes, symptoms and prevention measures of diphtheria.

(a) Write the name of primates existing on earth about 15 million years ago. Write its important characteristics also?
(b) (i) From where did the animals similar to human being meet?
(ii) In which sequence were neanderthal, homohabilis and homo erectus evolved on earth?
(iii) When did modern man evolve on this planet?

Explain the Megasporogenesis in flowering plants with the help of diagram.

Describe in detail about food chain and food web existing in an ecosystem.

What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?

If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

What do you understand by sex-determi-nation?###What is sex determination? Describe various types of sex determination