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 -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 0.1 individual per fruitfly per week
The death rate of a population is the number of individuals that die in a given time, divided by the number of individuals in the population. It is a per capita rate, expressed with respect to the members of the population.
\( \displaystyle \text{Death rate} = \frac{\text{number of deaths}}{\text{population size}} = \frac{4}{40} = 0.1 \)
So the death rate is 0.1 individual per fruitfly per week.
Option (1) 10 individual per fruitfly per week — Incorrect. 10 comes from dividing the population by the deaths (40 ÷ 4). The rate is the deaths divided by the population, not the other way round.
Option (2) 0.1 individual per fruitfly per week — Correct. Death rate is the number of deaths per individual in a given period. 4 deaths ÷ 40 flies = 0.1 individual per fruitfly per week.
Option (3) 1 individual per fruit-fly per week — Incorrect. A death rate of 1 would mean all 40 flies died in the week.
Option (4) 4 individual per fruitfly per week — Incorrect. 4 is the number of deaths, not the rate. It has not been divided by the population size.
Note: A similar question was also asked in CUET (UG) 2025 on 30-05-2025 (Slot 1) and on 23-05-2025 (Slot 2).
NCERT Extract:
Population Attributes – …
