If 4 individuals in a laboratory population of 40 fruitflies died during a specific time interval of one week. What will be the death rate of the population during that period?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 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) 1.0 individual per fruitfly per week — Incorrect. A death rate of 1.0 would mean all 40 flies died in the week.
Option (2) 4.0 individual per fruitfly per week — Incorrect. 4 is the number of deaths, not the rate. It has not been divided by the population size.
Option (3) 0.4 individual per fruitfly per week — Incorrect. 0.4 would need 16 deaths among 40 flies. (In the same book example, 0.4 is the birth rate of the lotus plants.)
Option (4) 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.
Note: A similar question was also asked in CUET (UG) 2025 on 26-05-2025 (Slot 2) and on 23-05-2025 (Slot 2).
NCERT Extract:
Population Attributes – …
