Internal structure of leaves
A cross-section of a leaf is studied under a microscope. The upper and lower surfaces of the blade are covered with epidermis (skin): its cells are tightly packed and almost transparent, so light passes inside; the epidermis protects inner layers from damage and drying out. The epidermis has pairs of bean-shaped guard cells with stomata between them; guard cells contain chloroplasts. Gas exchange and transpiration take place through the stomata. Between the layers of epidermis lies the mesophyll: cells rich in chloroplasts in several layers — elongated, column-like cells on top and round-oval cells below. Photosynthesis takes place in the mesophyll. Veins contain vessels (water and mineral salts), sieve tubes (organic matter) and mechanical fibres; together they form the vascular bundle.
| Part | Structure |
|---|---|
| Epidermis | upper and lower surface; has stomata |
| Mesophyll | column-shaped cells on top, rounded cells below |
| Veins | vascular bundles |
Slide: make a very thin section of a fresh leaf (e.g. a houseplant or radish leaf) and view it under the microscope (the teacher cuts). Or the nail-varnish method: paint clear nail varnish on the underside of a leaf, let it dry, lift the film with sticky tape and look for stomata under the microscope. Safety: use varnish only in fresh air under adult supervision, away from eyes and mouth; cutting tools only for the teacher.