Read the given passage and answer the following questions:
In nature, we rarely find isolated, single individuals of any species; majority of them live in groups in a well defined geographical area, share or compete for similar resources, potentially interbreed and thus constitute a population. A population has certain attributes whereas, an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births and deaths. The rates, hence, expressed are change in numbers (increase or decrease) with respect to members of the population. Here is an example. If in a pond there were 20 lotus plants last year and through reproduction 8 new plants are added, taking the current population to 28, we calculate the birth rate as 8/20 = 0.4 offspring per lotus per year. If 4 individuals in a laboratory population of 40 fruitflies died during a specified time interval, say a week, the death rate in the population during that period is 4/40 = 0.1 individuals per fruitfly per week. Another attribute characteristic of a population is sex ratio. An individual is either a male or a female but a population has a sex ratio (e.g., 60 per cent of the population are females and 40 per cent males). 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. 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.
What does an age pyramid reflect in a population?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The growth status
The passage states that when the age distribution of a population is plotted, the resulting structure is called an age pyramid, and that “the shape of the pyramids reflects the growth status of the population”: whether it is growing, stable or declining.
Option (1) The reproductive rate — Incorrect. The pyramid shows how many individuals are in each age group. It does not give a reproductive rate.
Option (2) The birth rate — Incorrect. The birth rate is a per capita rate worked out from births. A pyramid shows age groups, not a birth rate.
Option (3) The growth status — Correct. From the shape of the pyramid one can tell whether the population is growing, stable or declining.
Option (4) The death rate — Incorrect. The death rate is a per capita rate worked out from deaths. A pyramid does not show it directly.