Plant Structure
THE LEAF There are two basic types of leaves: simple and compound. Simple leaves have a flat, undivided blade while the blades are divided into leaflets in compound leaves. The leaf is the site of photosynthesis and is adapted for this function in a number of ways:
Q Flattened structure to give a large surface area
Q Presence of stomata for the exchange of gases
Q Thin to allow diffusion of carbon dioxide
Q Transparent epidermis to allow for light to travel through
Photosynthesis is the ability of plants to make their own food using light energy from the sun. It occurs in an organelle called a chloroplast, where a pigment called chlorophyll is essential for the process. The process of photosynthesis is represented chemically as follows: 6CO2 + 6H20 ✒ C6H12O6 + 6O2
The leaf possesses tiny openings called stomata, more of which are found on the lower surface of the leaf. The loss of water from the surface of the plant through these openings is called transpiration. The opening and closing of the stomata is controlled by special cells called guard cells.
The transpiration stream is the continuous flow of water from the roots up to the leaves of the plant where it is lost through evaporation. The rate of transpiration may be affected by both external and internal factors. External factors include light intensity, humidity and temperature. Internal factors include number, distribution and size of stomata.
Transpiration in any plant is significant as it ensures that water reaches the leaves of the plant and as it evaporates, it produces a cooling effect throughout the plant. The leaf is also involved in the exchange of gases and the storage of food.