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 the sex ratio of a population refer to?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The proportion of males and females in the population
The passage states that “an individual is either a male or a female but a population has a sex ratio”, and gives the example of 60 per cent of the population being females and 40 per cent males. So the sex ratio is the proportion of males and females in the population.
Option (1) The total number of males — Incorrect. The number of males alone is only one part. A ratio compares the males with the females.
Option (2) The total number of females — Incorrect. The number of females alone is also only one part, for the same reason.
Option (3) The proportion of males and females in the population — Correct. The sex ratio expresses the share of males and of females in the population, as in 60 per cent females and 40 per cent males.
Option (4) The reproductive capacity of individuals — Incorrect. Reproductive capacity is about how many offspring individuals can produce, not about how many males and females there are.