JAMB 2021 Biology · Question 40

The number of plant species obtained from a population study of a garden is as follows: Guinea grass (15)…

Question

The number of plant species obtained from a population study of a garden is as follows: Guinea grass (15), Ipomoea spp (5), Sida spp (7) and Imperata spp (23) What is the percentage of occurrence of Imperata spp?

A.35%
B.16%
C.46%
D.23%

Answer: C. 46%

Explanation written with AI and checked against the answer key

Analyze the question: We're asked for the percentage occurrence (relative abundance) of Imperata in the garden. This means its share of all the plants counted.

Concept: Percentage occurrence = (number of individuals of the species ÷ total number of individuals of all species) × 100

Solution:

Step 1: Find the total number of plants. 15 + 5 + 7 + 23 = 50

Step 2: Divide the Imperata count by the total. 23 ÷ 50 = 0.46

Step 3: Convert to a percentage. 0.46 × 100 = 46%

Answer: Option C (46%).

Why the other options are wrong:

D (23%) is just the raw count of Imperata, which you get if you forget to divide by the total.
A (35%) and B (16%) don't come from any correct calculation using these figures.

Exam tip: When the total comes to 50, finding a percentage is easy: just double the number. Here 23 × 2 = 46%. Always add up all the species first before dividing.

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