What is transpiration? We just studied that the transportation of food in plants occurs in phloem and its water occurs in xylem. Now we will discuss transpiration and the factors affecting it.
Plants continuously absorb water from the soil, but not all the water absorbed is used by the plant. Excess water evaporates from aerial parts of plants and mostly through the stomata. below the lamina of the leaf.
This process is called transpiration. Ever wondered how plants draw water up against the force of gravity? The evaporation of water from leaves results in a suction force, which pulls water up the xylem vessels.
This suction force is called transpiration pull. It is the main force that pulls water and mineral salts up the plant. This upward movement of substances is called the transpiration stream.
Factors affecting the rate of transpiration. Transpiration depends on evaporation. Therefore, factors affecting the rate of evaporation also affect the rate of transpiration.
These factors affecting the rate of transpiration are humidity, temperature, strong wind and light. Humidity of air. The intercellular spaces in the leaf are normally saturated with water vapor.
If the outside air is dry, water vapor will diffuse more rapidly out of the leaf, that is, the rate of transpiration will increase. Whereas, if the air is damp or humid, evaporation is limited. The more humid the air is, the slower is the rate of transpiration.
Temperature of the air Assuming all other factors remain constant, a rise in temperature of the surroundings will increase the rate of evaporation, and thus transpiration rate also increases. Strong wind When the air is still, transpiration makes the air around the leaves moist. The water vapors build up and increase the air humidity, hence, as we've stated before, reducing the transpiration rate.
During a windy day, the moist air around the leaf is blown away, making the air less humid. This increases the rate of transpiration. The stronger wind, the higher the rate of transpiration. However, if the wind is very strong, the stomata may close because the guard cells lose too much water. What would happen if there's a cool, wet wind?
Light. Light affects the size of the stomatal opening on the leaf, thus affecting the rate of transpiration. During the night or in the shade, the stomata close and reduce the rate of transpiration. but on a sunny day the stomata open wide and increase the rate. The movement of water vapor outward also removes heat from the plants, thereby cooling the leaves and preventing them from being scorched by the hot sun.