How it works
A leaf cell diagram: a typical broad leaf cut across and seen in section, its layers of cells from the waxy top surface down to the openings on its underside.
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Top to bottom
The cuticle's wax keeps water in. Under the upper epidermis, the tall palisade cells, packed with chloroplasts, do most of the photosynthesis. Below them the spongy mesophyll's loose cells leave air spaces for gases to move through.
Veins and stomata
A vein runs through the middle: xylem brings water in, and phloem carries sugars away. On the underside, each stoma sits between two guard cells, which open and close it.
- The cuticle is often thinner on the underside than on the top, and thicker on leaves from dry places than from wet ones.
Questions and answers
What are the layers of a leaf in order?
From the top: cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis and the lower cuticle. The veins run through the mesophyll.
Why do palisade cells have so many chloroplasts?
They sit just under the top surface, which faces the light, and they are the leaf's main photosynthetic cells.
What do guard cells do?
Each pair surrounds a stoma and opens or closes it by swelling or shrinking, letting gases in and out and controlling water loss.