Measurements of height and weight of students in a class show

Analyze the question: Height and weight are measured across students in a class. The question asks what this kind of data shows.

Concept: Variation within a population comes in two forms:

• Discontinuous variation: There are distinct categories with no intermediates. Examples are blood group (A, B, AB, O), sex, and the ability to roll the tongue. These traits are usually controlled by one or a few genes and are little affected by the environment.
• Continuous variation: The trait shows a full range of values between two extremes. Examples are height, weight, and skin colour. These traits are usually controlled by many genes (polygenic) and are strongly influenced by the environment, such as diet. A graph of the data gives a smooth bell-shaped curve (normal distribution).

Solution:

1. Height and weight are measured on a scale, for example 150 cm, 151 cm, 152.5 cm, and so on.
2. Students do not fall into just "tall" or "short". Most have in-between values, with a few very tall and a few very short students.
3. This smooth range of values is the mark of continuous variation.
4. Options C and D cannot be concluded from the data. Measurements alone do not tell us that shortness or fatness is more or less common.
5. Option A is wrong because discontinuous variation involves distinct groups with no intermediates.

Answer: **B. continuous variation.

Exam tip: If a trait can be measured (height, weight, foot length), it is continuous. If it can only be counted in categories (blood group, sex), it is discontinuous. A memory aid is "Continuous = Can measure."