IGCSE Biology (0610)

Reading a value from a graph

What this topic tests, the mistakes that cost marks, and one exam-style question worked through step by step.

Key ideas and common mistakes

To find a value from a graph, locate the given x-axis value, move vertically to the curve, then horizontally to the y-axis.
Common mistake: Students often misread by following the wrong axis or not aligning with the curve.
To estimate a value between plotted points on a graph, interpolate by finding the position between known values and use ruled lines to show how the value is read from the graph.
Common mistake: Students often guess or pick the nearest point instead of interpolating.
Linear interpolation between two plotted points on a straight-line graph is needed to estimate an intermediate value, and the correct method is to use construction lines from the x-axis up to the line and across to the y-axis.
Common mistake: Students often guess or misread without using this graphical method.
To compare values at a time not directly plotted, interpolate between the nearest data points for each batch.
Common mistake: Students who only use the closest plotted value or misread the graph may choose the wrong batch.
Estimating an intermediate value from a smooth curve requires interpolating between plotted points, not just averaging or picking the nearest value.
Common mistake: Students often ignore the curve's shape and use only the closest data point or a simple average.
To estimate a value between plotted points on a graph, interpolate smoothly along the curve rather than assuming a straight line or using only the nearest point, and always include the correct unit as shown on the axis label.

Worked example

State which batch of seedlings had the greater mean height on day 5.

Try it first, then show the working

batch B / the seedlings kept in the dark identified

Answer: Batch B, the seedlings kept in the dark

Try one yourself

Use the graph to read off the volume of oxygen released at a light intensity of 30 units.Answer it and get it marked → Use the graph to read off the volume of gas collected at a temperature of 40 °C.Answer it and get it marked → Use the graph to state the distance moved by the air bubble at a time of 4 minutes.Answer it and get it marked →

13 exam-style questions on Reading a value from a graph, each marked to the scheme.

Reading a value from a graph

Key ideas and common mistakes

Worked example

Try one yourself

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