Learning focus
Develop transferable AO3 skills: plan, measure, record, process, interpret and evaluate biological investigations accurately and safely.
Line graphs
Use a line graph when the independent variable is continuous numerical data, such as temperature, concentration or time. Plot measured points and draw a best-fit line or smooth curve as appropriate.
Bar charts
Use a bar chart for categories or discrete groups, such as species, treatment type or blood group. Bars have equal width and do not touch. The order may be arbitrary unless the categories have a natural sequence.
Histograms
Use a histogram for continuous data grouped into class intervals, such as height distributions. Bars touch because the scale is continuous. If class widths differ, frequency density may be needed, though simple equal intervals are most common at this level.
Pie charts
Pie charts show proportions of a whole. They are less useful for showing relationships between two measured variables. Select a display that answers the biological question rather than choosing the most decorative format.
Practical or data skill
Classify ten data sets as suitable for a line graph, bar chart, histogram or pie chart, and justify each selection using the variable type.
Examination tip
Continuous x-data usually requires a line graph; categories require a bar chart.
Review questions and suggested answers
Question 1
Why do histogram bars touch?
Suggested answer
The class intervals represent a continuous variable.
Question 2
When is a line graph suitable?
Suggested answer
When the independent variable is continuous numerical data.
Question 3
What is a key visual difference between a bar chart and histogram?
Suggested answer
Bar-chart bars have gaps; histogram bars touch.
