

Which leaf surface has more stomata? Pupils make leaf impressions, count pores at 100× magnification and compare their results in this KS3 virtual lab.
Pupils investigate the upper and lower surfaces of the same leaf. They start with a prediction and finish with a conclusion supported by their own counts. An interactive guard cell model then helps them explain why these tiny pores matter for gas exchange and water loss.
What pupils do
- Prepare two slides. Paint a patch of each leaf surface with clear nail varnish. Once it dries, use transparent tape to lift each impression and mount it on a labelled slide.
- Count the stomata. Adjust the fine focus on the virtual microscope and examine three fields of view per surface at 100× magnification. Pupils can tap each pore as they count. One pore surrounded by two guard cells counts as one stoma.
- Compare the evidence. Record all six counts, calculate the mean number of stomata per field for each surface and check both answers to one decimal place. Use the two means to decide whether the prediction was supported.
- Explore guard cell function. Open and close the pore in the model. Explain how an open pore allows carbon dioxide to enter the leaf and water vapour to escape.
Where it fits in your scheme of work
Use this alongside White Rose Science Year 8 Plants when teaching Adaptations of the leaf. For Exploring Science, including Exploring Science International, and AQA Activate, it supports lessons on leaf structure, gas exchange and photosynthesis. The investigation also gives pupils practice in microscopy, sampling and calculating a mean.
Classroom use
Project one microscope field and ask everyone to record a count before revealing the checked answer. Pupils can then complete a two-row results table on their worksheet or in their books. Finish by asking why the upper and lower surfaces must be compared using the same field size.
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