Biology 11–12 · Year 11

Stomatal density from nail-varnish leaf impressions

Module 2: Organisation of Living Things (Nutrient and Gas Requirements); also Module 3 (Adaptations)

Practical, model not builtLow risk

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The idea

Gas exchange in a leaf happens through stomata whose number per square millimetre can be measured from a surface impression and compared between leaf surfaces and species.

What you need

Leaves of three species, for example Tradescantia zebrina (a hole-punched disc of its leaf can be viewed directly with no impression or other preparation, as the SAPS resource notes), a eucalypt and a broad garden leaf
Clear nail varnish; clear adhesive tape; slides; scissors
Compound microscope with a calibrated field of view (stage micrometer or ruler at 40x)
Tally counter or spreadsheet

How to do it

Paint a thin patch of nail varnish about 1 cm square on the lower surface of a leaf and let it dry for 10 minutes; do the same on the upper surface.
Press tape over the dried varnish, peel it away and stick it to a slide.
Calibrate the field of view at 400x from the 40x measurement (diameter at 400x = diameter at 40x divided by 10) and calculate the field area as pi x (diameter/2)^2.
Count all stomata in the field in three separate places on each impression and record the mean.
Calculate stomatal density = mean count divided by field area, in stomata per square millimetre, for upper and lower surfaces of each species.
Compare species and surfaces and relate the pattern to habitat and water conservation.

What you should see

With a field diameter of 0.45 mm at 400x the field area is 0.159 square millimetres, and a mean count of 20 stomata gives 126 stomata per square millimetre (computed). Most broad-leaved plants show far more stomata on the lower surface than the upper; Tradescantia zebrina shows clearly outlined guard cell pairs among purple epidermal cells. The learner knows it worked when replicate fields on the same impression agree to within a few stomata and the lower-versus-upper difference is consistent across leaves of the same plant.

What changes

What you change: leaf surface (upper or lower) and plant species
What you measure: stomatal density (stomata per square millimetre)
What you keep the same: magnification and field area
leaf age and position on the plant
number of fields counted

Common misconceptions

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

Stomata are on the upper surface where the light is; in most plants they are mostly underneath.
Gas enters a leaf anywhere across its surface; the cuticle is nearly impermeable and stomata are the entry points.
More stomata always means more photosynthesis; density trades off against water loss.

Safety card

Low riskLearners carry it out

Hazards

Nail varnish solvent vapour
Plant sap may irritate skin

Controls

Ventilate the room and cap the bottle
Wash hands after handling leaves

Note

Nail varnish is a flammable solvent product: RiskAssess (https://www.riskassess.com.au/).

Curriculum references

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

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO11-9 BIO11-10 BIO11/12-4 BIO11/12-6
Biology 11–12 Syllabus (2025), Year 11 focus area Cells to systems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-02
Biology 11–12 Syllabus (2025), Year 11 focus area Evolution and ecosystems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-03
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-04 BI-11WS-06
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities