Students should be able to: • translate information between graphical and…

The idea

This skill underpins practical work on plant transport. Suppose a student measures the mass of a leafy shoot on a balance every 5 minutes as it transpires. They record a table of time in minutes and mass in grams, then translate that numerical data into a line graph: time on the x-axis, mass on the y-axis. Choosing a scale means making each axis span the data range with equal, labelled intervals, so the plotted points are spread out and easy to read. Extracting information means reading a value from the graph, such as the mass at 12 minutes, by interpolating between plotted points. Interpreting means explaining the trend, for example that mass falls fastest in warm, moving air because transpiration removes water vapour quickly.

What earns the marks

• Translate numerical data into a graph by placing the independent variable on the x-axis and the dependent variable on the y-axis, then plotting each pair of values as a point.
• Translate graphical information back into numerical form by reading values from axes, including interpolating between labelled points when the required value is not plotted directly.
• Select a scale for each axis that covers the full data range, uses equal intervals and makes efficient use of the available grid so points are clearly separated.
• Draw appropriate graphs for the data type, using a line graph with a line of best fit for continuous data and a bar chart for discrete categories.
• Extract information from charts and tables by identifying the relevant row, column or plotted point and quoting the value with its correct unit.
• Interpret trends and relationships, such as describing the rate of change from a graph gradient or explaining a pattern in terms of the underlying biology.

Common mistakes and how to put them right

• Plotting the independent variable on the y-axis instead of the x-axis.

  Put it right by deciding which variable the student changed and placing it on the x-axis.

• Choosing a scale with unequal intervals or one that leaves most of the grid unused.

  Put it right by counting the squares available and setting a regular interval that fills the axis.

• Reading a graph value by counting grid lines rather than using the labelled scale.

  Put it right by checking the value of each major division before estimating between them.

Exam tips

• Label both axes with the quantity and its unit, and give the graph a title that identifies what is being shown.
• When asked to read a value, show your working by marking the point on the graph and stating the value with its unit.
• For an interpretation question, quote specific data from the graph or table and link it to a biological process rather than describing the shape alone.