Learning focus
Develop transferable AO3 skills: plan, measure, record, process, interpret and evaluate biological investigations accurately and safely.
Continuous variation
Characteristics such as height or hand span show a range of numerical values and are influenced by many genes and environment. Measure a sufficiently large sample using a standardised technique and display grouped data in a histogram.
Discontinuous variation
Characteristics such as blood group or tongue-rolling category fall into distinct groups with no intermediate values. Record frequencies and use a bar chart because the categories are discrete.
Sampling and bias
A convenience sample may not represent the wider population. Define the population, use random or systematic selection where possible and keep measurement technique consistent. Obtain consent for human measurements.
Interpretation
Describe distribution shape, range, mode and overlap. Do not claim that a difference is genetic unless environmental influences and evidence are considered. Correlation does not establish causation.
Practical or data skill
Collect an ethical class data set for one continuous characteristic and one discontinuous characteristic. Select and justify the correct chart.
Examination tip
Histogram bars touch because the measured variable is continuous.
Review questions and suggested answers
Question 1
Give one example of continuous variation.
Suggested answer
Height, mass, hand span or another continuously measured characteristic.
Question 2
Which display suits discontinuous categories?
Suggested answer
A bar chart.
Question 3
Why is a large sample useful?
Suggested answer
It better represents variation and reduces the influence of unusual individuals.
