Reproduction in organisms — BIOLOGY STD 12 Science — Question

In a typical nucleus some regions of chromatin are stained light and others dark. Explain why it is so and what is its significance.

Study the population growth curves in the graph given below and answer the questions which follow:

1. Identify the growth curves ‘a’ and ‘b'.
2. Which one of them is considered a more realistic one and why?
3. If dN/dt=rN(K-N/K) is the equation of the logistic growth curve, what does K stand for?
4. What is symbolised by N?

Describe the habitat of microbes. Why are they grown on nutrient media? Explain.

Study the figure given below and answer the following questions.

1. Name the molecule 'X' synthesised by i gene. How does this molecule get inactivated?
2. Which one of the structural genes codes for B-galactosidase?
3. When will the transcription of this gene stop?

What is advantage of cross-breeding in cattle?

A woman has certain queries as listed below, before starting with contraceptive pills. Answer them.
What schedule should be followed for taking these pills?

1. Mention the exact location or the site in a flowering plant, where the following developments take place:

1. Deposition of sporopollenin.
2. Triple fusion.
3. Release of male gametes.
4. Megasporogenesis.

2. Draw a labelled diagram of a male gametophyte of an angiosperm.

1. Name the organic material exine of the pollen grain is made up of. How is this material advantageous to pollen grain?
2. Still it is observed that it does not form a continuous layer around the pollen grain. Give reason.
3. How are 'pollen banks' useful?

How biodiversity is important for functional ecosystem?

How can Hardy-Weinberg equilibrium be affected? Explain giving three reasons.