Leaf Structure and Adaptations

Leaves are the primary organs of photosynthesis in a plant. Their structure is beautifully adapted to maximise the rate of photosynthesis while minimising water loss. This lesson covers the detailed structure of a leaf in cross-section and explains how each part is adapted for its function, as required by Edexcel GCSE Biology (1BI0) Topic 6.

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Overview of Leaf Structure

When you look at a leaf under a microscope (in cross-section), you can see several distinct layers. From the top to the bottom, these are:

1. Upper epidermis (with waxy cuticle)
2. Palisade mesophyll
3. Spongy mesophyll
4. Lower epidermis (containing stomata and guard cells)
5. Vascular bundles (veins — xylem and phloem)

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The Waxy Cuticle

• A thin, waterproof layer of wax produced by the upper epidermal cells
• Function: Reduces water loss by evaporation from the upper surface of the leaf
• It is transparent, allowing light to pass through to the photosynthetic cells beneath
• The cuticle is generally thicker on the upper surface (which faces the sun and is more exposed to the air)