Human Reproduction — BIOLOGY STD 12 Science — Question

If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

For selection of recombinants, insertional inactivation of antibiotic marker has been superceded by insertional inactivation of a marker gene coding for a chromogenic substrate. Give reasons.

What is ecological pyramid? Write its types and give a diagrammatic representation of the pyramid of biomass in the ocean.

Placenta acts as an endocrine gland. Explain.

The number of trophic levels in an ecosystem are limited. Comment.

Study the table given below and answer the questions that follow:

Species A	Species B	Name of interaction
(+)	(+)	(A)
(-)	(-)	(b)
(+)	(-)	(c)
(+)	(0)	(d)

+ = Beneficial interaction
- = Detrimental interaction
0 = Neutral interaction
Identify a, b, c and d in the given table and explain any three of them with the help of an example each.

Write two differences between spermatogenesis and oogenesis.

Give details of different types of immune globulins in humans.

Using a flow chart explain the process of decomposition. List the factors which affect this process.

List the harmful effects caused by alcohol/drug abuse.