Human Reproduction — BIOLOGY STD 12 Science — Question

1. Why are catalytic converters recommended for vehicles?
2. Why should such vehicles use only unleaded petrol?
3. Why is CNG preferred to diesel as a fuel in vehicles?

Explain why a recessive allele is unable to express itself in a heterozygous state.

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

What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle?

What is menstrual cycle. Explain its various events with the help of diagram.###Describe in detail the various stages of menstrual cycle with the help of diagram.###Write a detail note on different stages of menstrual cycle and also sketch out these stages of
menstrual cycle by graphical diagram.###Define sexual reproduction. Explain the process of menstrual cycle.

What role does pituitary gonadotropins play during follicular and ovulatory phases of menstrual cycle and also explain the shift in steroidal secretions.

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.

Describe in detail the development of female gametophyte in angiosperm with well labelled diagram.###Explain in the process of Megasporogenesis in a typical angiosperm plant by drawing the well labelled diagram of mature embryo sac.

During the course of evolution why DNA was chosen over RNA as genetic material? Give reasons by first discussing the desired criteria in a molecule that can act as genetic material and in the light of biochemical differences between DNA and RNA.

How are Mendelian inheritance, polygenic inheritance and pleiotropy different from each other?