OCR Gateway Science - B4a

Leaves all: - have the same basic structure, - carry out photosynthesis

Although they are all different colours, they all contain the green pigment, chlorophyll which traps sunlight and produces food for the plant.

In Autumn, chlorophyll is the first structure to break down, which reveals other pigments: red, orange, yellow.

This diagram shows the internal structure of a leaf.

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There are no cells in the cuticle. It is a waxy layer which helps to prevent water loss.

Photosynthesis:

carbon dioxide (6CO2) + water (6H2O) = glucose (C6H1206) + oxygen (6O2)

Glucose = used for respiration and converted into other substances for storage and use in the cell.

Oxygen = released into the air or used in respiration

Adaptions of leaves:

• broad: gives large surface area to absorb sunlight
• thin: short distance for gases to diffuse
• chloroplasts: contain chlorophyll - traps sunlight
• Stomata: allow gases to diffuse in/ out through the lower epidermis

The leaf is adapted at a cellular level to improve thefficiency of photosynthesis:

• Transparent upper epidermis (no chloroplasts): allows light to enter through the palisade mesophyll layer below.
• Palisade measophyll is near the top: contains the most chloroplasts to trap light energy and photosynthesise.
• Air spaces in the spongy mesophyll: allows diffusion of gases between the stomata and the photosynthesising cells in the mesophyll layers.
• Very large internal surface area to volume ratio: gives more surface area for absorption of CO2 from air spaces
• Guard cells: control the opening and closing of stomata for the entry and release of gases.