If there were 100 rose plants in a garden last year. 20 new rose plants are added through reproduction in current year. The birth rate of rose is ________ offspring per rose per year.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.2
Birth rate = number added by reproduction ÷ population at the start = 20 ÷ 100 = 0.2 offspring per rose per year.
Option (1) 0.5 — Incorrect. It would need 50 new plants.
Option (2) 5.0 — Incorrect. It is 100 ÷ 20, the division the wrong way round.
Option (3) 0.02 — Incorrect. It is ten times too small; it would mean only 2 new plants.
Option (4) 0.2 — Correct. Birth rate is the number of births per individual in a given period. 20 new plants ÷ 100 plants = 0.2 offspring per rose per year.
NCERT Extract:
Population Attributes – “… 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.”