Members of a population are arranged as per their age group. Select the expanding population from the following situations.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Pre-reproductive age > Reproductive age > Post reproductive age
An age pyramid is drawn from the per cent of individuals in each age group: pre-reproductive at the base, reproductive in the middle and post-reproductive at the top. Its shape shows whether a population is growing, stable or declining.
Option (1) Reproductive age > Post reproductive age > Pre-reproductive age — Incorrect. Here the young are the fewest. Fewer individuals will enter the reproductive age, so the population will shrink.
Option (2) Post reproductive age > Pre-reproductive age > Reproductive age — Incorrect. Here the old are the most numerous and the reproductive group is the smallest. Such a population cannot grow.
Option (3) Pre-reproductive age > Reproductive age > Post reproductive age — Correct. The pyramid has a broad base of young individuals. When they grow up, more individuals will reproduce, so the population is expanding.
Option (4) Post reproductive age < Pre-reproductive age = Reproductive age — Incorrect. When the young are about equal to the reproductive group, each generation only replaces the one before. That is the shape of a stable population.
NCERT Extract:
Population Attributes – “… A population at any given time is composed of individuals of different ages. If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid (Figure 11.1). For human population, the age pyramids generally show age distribution of males and females in a diagram. The shape of the pyramids reflects the growth status of the population - (a) whether it is growing, (b) stable or (c) declining.”
