The Structure of a Leaf

The leaf is where photosynthesis takes place. It has many adaptations to make it perform its job better.

• The leaf has a waxy cuticle to stop it losing water and drying out.
• The epidermis is a protective layer of cells and contains no chloroplasts.
• The palisade layer contains the most chloroplasts as it is near the top of the leaf. The chloroplasts contain the pigment chlorophyll. It is here that photosynthesis takes place.
• The palisade cells are arranged upright. This means the light has to pass through the cell lengthways and so increases the chance of light hitting a chloroplast and being absorbed.
• The spongy layer contains fewer chloroplasts, enough to catch what the palisade layer cannot absorb.
• The spongy layer has air spaces to make it easier for gases to circulate in the leaf.
• The vascular bundle provides the leaf with water via the xylem vessels. Food, such as sugar, made in the leaf is transported in the phloem vessels to the rest of the leaf.
• The stomata (stoma - singular) are tiny pores that allow carbon dioxide to enter the leaf while oxygen leaves the leaf.
• Guard cells can open or close the stomatal pores to regulate how much gas can enter or leave the leaf. At night the pores close, opening in the daytime.

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2005 Psionica