Human Reproduction — BIOLOGY STD 12 Science — Question

a. Where is microsporangium located in an angiosperm? State the functions of tapetum and the other three layers of microsporangium.
b. Describe the structure of the male gametophyte produced as a result of microsporogenesis.
c. State the functions of each part of the male gametophyte.

Ranjana and Shilpi had a hot argument whether or not life is still originating on the earth today. Their neighbour, Mr. Kamal Mishra, a retired professor, who happened to be listening to the girls, called them and explained the matter in detail.

1. As a student of biology, what is your answer to the above problem? And why?
2. Recall the experiment of Miller, which simulated the primitive atmosphere.

1. What were the products obtained in his experiment?
2. How was energy provided in the experiment?

3. What would have been the energy source for origin of life on the earth?
4. Indicate the values shown by Mr. Kamal Mishra?

Answer the following questions:
Seeds offer several advantages to angiosperms. Describe any three such advantages.

1.  

1. Name the biogeochemical (nutrient) cycle shown below:
2. Name an activity of the living organisms not depicted in the cycle by which this nutrient is returned to the atmosphere.

2. How would the flow of nutrient in the cycle be affected due to large scale deforestation? Explain giving reasons.
3. Describe the effect of an increased level of this nutrient in the atmosphere on our environment.

A.
(i) Why is there a need to conserve biodiversity? (Any two reasons)
(ii) Name and explain any two causes that are responsible for the loss of biodiversity.

List 10 modern day animals and using the various resources available link it to a corresponding ancient fossil. Name both of them.

With the help of a diagram explain the structure of DNA.

Describe the advantages for keeping the ecosystems healthy.