IGCSE Biology (0610)

Transpiration and factors affecting it

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

Key ideas and common mistakes

Transpiration is the specific process where water vapour exits a plant through stomata by diffusion, not to be confused with evaporation from soil or other plant surfaces.
To find the mean rate of water loss, subtract the final mass from the initial mass to get total loss, then divide by the time interval.
Common mistake: Students often forget to divide by time or use the wrong mass difference.
To calculate a rate from a table, divide the measured distance by the given time and match the answer's decimal places to the other values in the table.
Common mistake: Students often forget to use the correct number of decimal places for consistency.
Identifying other environmental factors that affect transpiration rate, specifically those that influence evaporation or the diffusion gradient, not just humidity.
Common mistake: Students often incorrectly name unrelated factors like soil type or plant species.
To read a value from a graph, locate the correct position on the x-axis (here, time = 30 minutes), then move vertically to the plotted line and horizontally to the y-axis.
Common mistake: Avoiding misreading grid intervals or misaligning axes.
A higher temperature increases the rate of transpiration, so the 35 °C line has the same shape as line A but lies above it at all times. The common mistake is to draw a line below A or one with a different shape.

State the name of the process by which water vapour is lost from plant leaves.

Try it first, then show the working

Answer: Transpiration

18 exam-style questions on Transpiration and factors affecting it, each marked to the scheme.