LEAF PHYSIOLOGY

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Describe how the internal and external structure of the leaf is designed to maximise photosynthesis.

Structure:

Thin waxy cuticle; Only one layer of transparent upper epidermis; Several layers of palisade cells with many chloroplasts; large vacuole to push the chloroplast to the edge of the cell; Specialised pigments to maximise photosynthesis; Big intercellular air spaces for gaseous exchange.

External:

Big surface area to maximise the absorption of light; Petiole to hold lamina out into the light; Leaves move to face the sun.

Describe how the internal and external structure of the leaf is designed to minimise transpiration. Draw diagram of a leaf showing stomata

Stomata Closure: Stomata are mostly found on the under surface of leaves and are the main exit point of water from the plant (gases: oxygen/carbon dioxide both in and out). They control water loss by closing at night (open during the day) also if the leaf wilts the stomata loses its turgidity and so will close (extreme mid-day heat can cause stomata to close).

Leaf Adaptations Limiting Water Loss: Common in plants from warm or windy climate, RHS – Thick waxy cuticle to reduce evaporation, e.g., Echeveria elegans;

RHS – Reduced leaf surface area, conifer needles; Pinus sylvestris RHS – Leaves covered in hairs to keep humidity close to the area of the stomata; Salvia argentea

Having fewer stomata; Having deep or extensive root systems; Having light, silver/grey foliage to reflect heat; Sunken stomata;Leaves that roll with the stomata on the inside, some grasses, e.g., Festuca glauca; Structural adaptations, e.g., Spartium junceum (Spanish broom) has very small leaves but the stem is dark green and photosynthesises; Spines, e.g., Opuntia polyacantha.