Leaf structure By Martin Samaj Leaf basics Above

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