Human Reproduction — BIOLOGY STD 12 Science — Question

What are selectable markers? Give examples.

What characteristics make a community stable?

List the Salient Features of Human Genome

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 response called? How does the body produce it?

The study of:

1. Fossils of dinosaurs.
2. Forelimbs of Cheeta, bat and human.
3. Thorns of Bougainvillea and tendril of Cucurbita shows that evolution of life forms has indeed taken place on earth. Explain.

Explain the primary productivity of ecosystem.

Study the graph given below and answer the question that follow:

1. Write the status of food and space in the curves (a) and (b).
2. In the absence of predators, which one of the two curves would appropriately depict the prey population?
3. Time has been shown on X-axis and there is a parallel dotted line above it. Give the significance of this dotted line.

In the 1950s, there were hardly any mosquitoes in Delhi. The use of pesticide DDT on standing water killed their larvae. It is believed that now there are mosquitoes because they evolved DDT resistance through the interaction of mutation and Natural selection. Pointwise, state in a sequence how that could have happened.

The graph given below shows species-area relationship of a certain region.

a. Study the graph and explain what it represents.
b. After a while, a small area was taken for constructing a road which divided the region into two. Write the impact this construction would have on species richness of the region.

Why are menstrual cycles absent during pregnancy.