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, the birth rate would be:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0.4 offspring per lotus per year
The birth rate is the number of births per member of the population in a given period.
New plants added by reproduction = 8.
Population at the start = 20.
Birth rate = 8 ÷ 20 = 0.4 offspring per lotus per year.
Option (2) 0.8 offspring per lotus per year — Incorrect. It divides by 10 instead of the starting population of 20.
Option (3) 0.5 offspring per lotus per year — Incorrect. 0.5 would need 10 births in 20 plants.
Option (4) 0.2 offspring per lotus per year — Incorrect. 0.2 would need only 4 births.
Note: A similar question was also asked in CUET (UG) 2026 on 19-05-2026 (Slot 2), and in CUET (UG) 2025 on 22-05-2025 (Slot 2) and on 16-05-2025 (Slot 1).
NCERT Extract:
Population Attributes – “… 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.”