Leaf Structure (Cambridge (CIE) IGCSE Biology): Revision Note

Wax cuticle

Protective, waterproof layer on top of the leaf that reduces water loss by evaporation, helping maintain the water needed for photosynthesis

Upper epidermis

Thin and transparent, allowing light to pass through to the palisade mesophyll beneath

Palisade mesophyll

Column-shaped cells tightly packed with chloroplasts to absorb as much light as possible, maximising the rate of photosynthesis

Spongy mesophyll

Contains large air spaces between cells, increasing the surface area available for gas exchange, so carbon dioxide can diffuse quickly to the palisade cells and oxygen can diffuse out

Lower epidermis

Contains stomata and guard cells, which control gas exchange and water loss (see below)

Guard cell

Changes shape as it absorbs or loses water, causing the stomata to open or close. This controls the diffusion of carbon dioxide in and oxygen out, and helps regulate water loss

Stomata (singular: stoma)

• Small pores that allow gas exchange between the leaf and the atmosphere

• Usually open during the day and closed at night, matching when photosynthesis occurs

• Also the main site of water loss by transpiration

• In most plants, found in higher numbers on the lower epidermis to reduce water loss (less exposure to direct sunlight/heat)

Vascular bundle

Contains xylem and phloem, which transport substances to and from the leaf

Xylem

Transports water (and dissolved mineral ions) up to the mesophyll cells for use in photosynthesis, and to replace water lost during transpiration

Phloem

Transports sucrose and amino acids around the plant (translocation), including away from the leaf to where they are needed or stored

Large surface area (leaf)

Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis

Thin

Allows carbon dioxide to diffuse to palisade mesophyll cells quickly

Chlorophyll

Absorbs light energy so that photosynthesis can take place

Network of veins

Allows the transports of water to the cells of the leaf for photosynthesis and carbohydrates (as a product of photosynthesis) away from the leaf

Stomata (singular: stoma)

Allows carbon dioxide to diffuse into the leaf and oxygen to diffuse out

Epidermis is thin and transparent

Allows as much light as possible to reach the palisade cells

Thin cuticle made of wax

To protect the leaf without blocking sunlight

Palisade cell layer (tissue) at the top of leaf

Maximises the absorption of light as it will hit chloroplasts in the cell directly

Spongy layer

Air spaces allow carbon dioxide to diffuse through the leaf, increasing the surface area

Vascular bundles

Thick cell walls of the tissue in the bundles help to support the stem and leaf