Question

Assertion: Bell shaped age pyramid represents a stable population.
Reason: In a stable population, proportion of individuals in reproductive age group is higher than the
individuals in the pre-reproductive age group.
A. Both Assertion and Reason are correct and Reason is the correct explanation for the Assertion.
B. Both Assertion and Reason are correct and Reason is not the correct explanation for the
Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Hint:-A population can be defined as a group of individuals of the same species living in a particular place at the same time. They may differ in their number, patterns of living together, behavior and organization.

Complete step-by-step solution:-
- The individuals of a population are divided into three ecological stages- pre-reproductive, reproductive and post-reproductive. The individuals of pre-reproductive are young, those of reproductive are mature and those in post-reproductive are old.
- Age pyramid is a model in which the number or proportions of individuals in various age groups at any given time are geometrically presented. In an age pyramid, the number of pre-reproductive individuals is shown at the base of the reproductive age group in the middle and the number of post-reproductive individuals at the top. The age pyramids indicate whether a population is expanding, stable or diminishing. The various types are:
- The age pyramid having broad base signifies a high percentage of young individuals and an exponential growth of population due to high birth rate, e.g. yeast, housefly, etc.
- Bell-shaped age pyramid shows a stable population with almost equal numbers of young, and middle aged individuals. The post-reproductive individuals are the smallest in numbers.
- Pyramid with a narrow base or urn-shaped pyramid shows increased numbers of middle-aged and old organisms as compared to young ones in the population. This shows the diminishing of the population.
So, the correct answer is C. Assertion is correct but Reason is incorrect.

Note:- The distribution of different age group individuals in a population may be constant or variable and it is directly related with the growth rate of that population. Rapidly increasing population must have a larger number of younger individuals.