Agriculture and Food 7–12 · Years 9–10

Counting stomata with leaf surface impressions

Plant Production 1

Practical, model not builtLow risk

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The idea

Stomata are the pores that let carbon dioxide in and water vapour out, and in most dicot leaves they are more numerous on the lower surface than the upper, while monocot leaves have them more evenly spread.

What you need

leaves of a dicot crop or garden plant (bean, geranium) and a monocot (wheat, spider plant)
clear nail varnish or a liquid skin-dressing product (the SAPS alternatives)
clear sticky tape, microscope slides
compound microscope with x10 and x40 objectives
stage micrometer to calibrate the field of view

How to do it

Paint a patch about 1 cm square on the upper and lower surfaces of each leaf and let it dry for 5 to 10 minutes.
Press clear tape onto each patch, peel the impression off and stick it to a labelled slide.
Use the stage micrometer to measure the diameter of the field of view at the magnification used for counting.
Count the stomata in five fields of view on each impression, moving to a new area each time.
Calculate the mean count and convert it to stomata per square millimetre with the model.
Compare upper and lower surfaces and dicot and monocot leaves, and relate the pattern to water loss.

What you should see

For the dicot leaves the lower surface has more stomata per square millimetre than the upper surface; the monocot leaves have a more even count on both surfaces, as the SAPS background describes. With a field of view 0.40 mm across (area 0.1257 mm^2), a mean of 30 stomata per field is 239 stomata per mm^2. The learner knows it worked when the five fields on one impression give similar counts and the calibration is checked against the stage micrometer.

What changes

What you change: leaf surface (upper or lower) and plant type (dicot or monocot)
What you measure: stomata per mm^2
What you keep the same: same magnification and calibrated field
five fields per impression
leaves of similar age and position

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Stomata are holes that stay open all the time.
Leaves take in water through their stomata.
Both surfaces of a leaf are the same.

Safety card

Low riskLearners carry it out

Hazards

nail varnish is flammable and its vapour irritates
glass slides

Controls

small volumes in a ventilated room away from flames
handle slides by the edges

Note

Solvent-based varnish: NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1 (general information for all staff) and Volume 2 Appendix D (generic risk assessment advice for each chemical). Complete a CSIS or RiskAssess site-specific risk assessment before the lesson.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Agricultural Technology Years 7–10 Syllabus (2019)AG5-11 AG5-12
Agriculture Technology 7–10 Syllabus (2024), new syllabus, implementation from 2027AGT5-APG-01
Australian Curriculum v9AC9TDE10K04AC9S10I03

Sources

The pages the author read to write this activity.

All Concept Studio activities