If last year, there were 80 lotus plants in a lake. Then, 16 new lotus plants were added through reproduction and the current population is 96 now. The birth rate of lotus plant is-
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0.2 offspring per lotus per year
Birth rate = new plants added ÷ population at the start
= 16 ÷ 80 = 0.2
Option (1) 0.2 offspring per lotus per year — Correct. Birth rate is the number of births per member of the starting population in a given time. Here 16 new plants came from 80 plants in one year, so 16 ÷ 80 = 0.2 offspring per lotus per year, just as NCERT works out 8/20 = 0.4 for its pond.
Option (3) 5 offspring per lotus per year — Incorrect. This is 80 ÷ 16, the division the wrong way round.
NCERT Extract:
Population Attributes – “… 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.”