Leaf structure By Martin Samaj

Leaf basics Above ground plant organ specialized for photosynthesis Leaves are the site where transpiration and guttation takes place Leaves can store food and water, in other plants they can serve different purposes

Leaf anatomy Leaf of an angiosperm consists of: Petiole (leaf stem) Lamina (leaf blade) Stipules Leaf consists of the following tissues: Epidermis Mesophyll Arrangement of veins

Leaf anatomy

Epidermis Outer layer of cells covering the leaf, covered by a thick waxy cuticle It isolates the plant’s inner parts from the outside Serves several functions: regulation of gas exchange, secretion of metabolic compounds, prevents water loss from the upper surface

Mesophyll Palisade mesophyll consists of densely packed cylindrical cells with many chloroplasts Palisade mesophyll is the main photosynthetic tissue and is positioned where the light intensity is the highest Spongy mesophyll consists of loosely packed cells with few chloroplast This tissue provides the main gas exchange surface

Leaves and transpiration Photosynthesis depends on gas exchange over a moist surface. Spongy mesophyll cells provide this surface Water often evaporates from the surface and is lost and this process is called transpiration Transpiration is the loss of water vapor from the leaves and stems of plants

Factors affecting transpiration The rate of water loss through transpiration depends on internal and external conditions Abiotic factors that have effect on the rate of transpiration There are 4 main factors: Light, Temperature, Humidity and Wind

The 4 abiotic factors Light - gurad cells close the stomata in the night = greater rate of transpiration Temperature - as the temperature rises the rate of transpiration increases  Humidity - The lower the humidity outside the leaf the faster the rate of transpiration Wind - Wind blows the saturated air away and so increases the rate of transpiration