Plants need a large surface area to volume ratio to maximise photosynthesis and to capture as much light as possible.Majority of water loss occurs through the leaves.In order to reduce water loss:1. Leaves have a waterproof waxy cuticle. 10% of water loss may still occur through the surface even with a cuticle.2. The stomata can be closed when necessary.3. Most of the stomata on the lower surface of the leaves away from direct sunlight.4. Xerophytes are plants that live in hot, dry climates and are adapted to reduce water loss by transpiration.Xerophytes may have1. A thick cuticle to reduce water loss by evaporation.2. Rolled up leaves to trap water vapour so an area of high water potential is directly outside the leaf. This reduces the water potential gradient between the inside and outside of the leaf.3. Most of the stomata on the lower epidermis of the leaves.4. Hairy leaves to trap moist air next to the leaf surface and reduce the water potential gradient between the inside and outside of the leaf.5. Sunken stomata. Having stoma in pits and groves can trap moist air next to the stomata and reduce the water potential gradient between the inside and outside of the leaf.6. Small, needle-like leaves reduce the surface area for diffusion. This needs to be balanced with the need for a large surface area for photosynthesis but plants that have rolled leaves or needles usually live in areas of high light intensity.
Limiting Water Loss in Plants
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Specification: AQA Biology (7401), AS-level, 3.3.1 Surface area to volume ratio. Topic: Exchange of Gases.
Key terms in this lesson
- diffusion
- The net passive movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.
- water potential
- The pressure created by water molecules, a measure of the tendency of water to move out of a solution; pure water has a water potential of zero and solutes make it more negative.
- surface area to volume ratio
- The ratio of an organism's or structure's external surface area to its total volume, which decreases as size increases.
- transpiration
- The evaporation of water from the leaves of a plant, which pulls water up through the xylem.
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All 28 lessons in Exchange of Gases · All AQA AS-level Biology topics