Human Reproduction — BIOLOGY STD 12 Science — Question

What are contraceptive pills? How do they function ?

Write a short note on hormones secreted during pregnancy.

Three water samples namely river water, untreated sewage water and Secondary effluent discharged from Sewage treatment plant were subjected to BOD test. The samples were labelled in A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:
i. Bacteria
ii. Banyan
iii. Deer
iv. Fish

What are methanogens? Name the animals they are present in and the role they play there.

A cross was carried out between two pea plants showing the contrasting traits of height of the plant. The result of the cross showed 50% of parental characters.

1. Work out the cross with the help of a Punnet square.
2. Name the type of the cross carried out.

What is the difference between endemic and exotic species?

Not all hydrophytes are pollinated by water. Justify by giving two examples.

Why do moss plants produce very large number of male gametes? Provide one reason. What are these gametes called?

A student on a school trip started sneezing and wheezing soon after reaching the hill station for no explained reasons. But on return to the plains, the symptoms disappeared. What is such a esponsecalled? How does the body produce it?