The Leaf Structure

Leaf adaptation to photosynthesis:

Photosynthesis is a process whereby green plants uses light energy to convert CO2 and H2O into

various organic compounds such as glucose,fructose and protein.

The leaf functions as the photosynthetic organ.This is because photosynthesis usually occurs in mesophyll cells of leaf.Mesophyll cells can be categorised into spongy mesophyll and palisade mesophyll cells.Just beneath the upper epidermis is the layer of closely packed elongated palisade mesophyll cells.The epidermis layer is a protective layer that is transparent to allow sunlight to penetrate through it.It also secretes a waxy material called cuticle to the leaf surface to prevent excessive loss of water.Water is one of the raw materials of photosynthesis.It is supplied to the leaf by the xylem vessels which transport water as well as mineral salt from the root to other parts of the plant like the leaf.The palisade mesophyll cells have a lots of chloroplasts which are double-membrane organelle which contains green pigment,chlorophyll.Chlorophyll molecules trap and absorb sunlight for phtochemical reactions.There are also accessory pigments like carotenoids in the chloroplast to absorb light of different wavelengths. Ironically,irregularly-shaped spongy mesophyll cells are loosely packed with air spaces.This allows gaseous exchange to be carried out efficiently in the mesophyll. This is important so that by-product of photosynthesis, O2 can passed out through the stomata.Stoma is a pore surrounded by two guard cells to enable transpiration and gaseous exchange.Guard cells regulate the opening of and closure of stomata. CO2 enters the leaf through stomata.The large surface area of the leaf allows maximum exposure to the sunlight and for gas exchange.The synthesised food is transported to other parts of the plant for utilised or storage by phloem sieve tubes.this process is known as translocation.