Leaf structure and stomatal density – leaf cross-section and a nail-varnish leaf cast
BiologyPlant PhysiologyAges 16–17
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Sign in to playThree screens on the leaf as the organ of photosynthesis: a leaf cross-section with cuticle, epidermis, palisade and spongy mesophyll, air spaces, vascular bundle and stomata, where you click each tissue to see its function, watch the paths of gases, light and water, and test yourself on the names; a practical counting stomata on a nail-varnish cast under the microscope and calculating density = number of stomata ÷ field area (πr²); and a comparison of stomatal density on the upper and lower surfaces of five species.
Lesson: Leaf structure and adaptations for photosynthesis and gas exchange; stomatal density
What it shows
This simulation shows how the structure of a leaf suits it for photosynthesis and gas exchange, for ages 14–18. Students explore a labelled cross-section, find the function of each tissue and watch carbon dioxide, oxygen, water vapour, light and water move through the leaf. In a virtual practical they make a nail-varnish cast, count stomata in fields of view of known diameter, calculate stomatal density per mm² and compare the upper and lower surfaces of five species. Model: the section is a simplified diagram and densities are typical published values with random field-to-field variation.
How to use
On Leaf cross-section, click a tissue or its button, choose what to Show and switch Stomata between open and closed; press Test yourself to name the highlighted tissue. On Stomatal count, choose Plant species, Leaf surface and Objective, press Make a nail-varnish cast, click each stoma to count it, then Record count and Next field. On Compare species, press Add class data and read the chart.
Parameters you can change
- Starting screen Leaf cross-section, Stomatal count, Compare species
- Shown on the cross-section Structure only, Gas exchange, Light entering the leaf, Water and sugar
- Stomata Open (daytime), Closed (night, water shortage)
- Plant species Bean (Phaseolus vulgaris), Sunflower (Helianthus annuus), Oak (Quercus robur), Maize (Zea mays), Water lily (Nymphaea)
- Leaf surface Lower surface, Upper surface
- Objective lens (×10 eyepiece) ×40 – field diameter 0.45 mm, ×10 – field diameter 1.8 mm
- Random seed (same number, same cast) 1–9999
Questions to explore
- Why is the palisade mesophyll just below the upper epidermis and packed with chloroplasts?
- Why do most land plants have more stomata on the lower surface, while a water lily has them only on the upper surface?
- Why should you count several fields of view and take a mean when measuring stomatal density?
