Transpiration

The Process of Transpiration:

1. Water Absorption:

• Water enters the plant through the root hair cells, which absorb water from the soil by osmosis.
• The water then moves across the root cortex and into the xylem vessels, which transport water up through the plant.

2. Water Transport:

• The xylem vessels carry water from the roots to the leaves. The water is drawn up through the plant due to capillary action and the transpiration pull created by water evaporating from the leaves.

3. Evaporation and Loss:

• Water evaporates from the surfaces of the spongy mesophyll cells in the leaves and diffuses out of the leaf through tiny openings called stomata.
• The loss of water vapour from the stomata creates a negative pressure within the leaf, pulling more water up through the xylem from the roots.

Factors Affecting Transpiration:

1. Light Intensity:

• Increased light leads to higher rates of transpiration because stomata open wider to allow more carbon dioxide in for photosynthesis, which also increases water loss.
• Decreased light results in lower transpiration rates as stomata tend to close.

2. Temperature:

• Higher temperatures increase the rate of transpiration by causing water to evaporate more quickly from the leaf surface.
• Lower temperatures reduce the rate of evaporation and, therefore, transpiration.

3. Humidity:

• High humidity lowers the rate of transpiration because the air is already saturated with moisture, reducing the concentration gradient for water vapour between the leaf and the air.
• Low humidity increases the rate of transpiration as dry air encourages more water to evaporate from the leaf.

4. Wind Speed:

• Increased wind speed can remove the humid air surrounding the leaf, increasing the concentration gradient and thus the rate of transpiration.
• Low wind speed leads to a build-up of moisture around the stomata, reducing transpiration.

5. Water Availability:

• Ample water supply ensures that the plant can maintain transpiration. If water is scarce, the plant may close its stomata to conserve water, reducing the rate of transpiration.

6. Poor airflow

• The water vapour surrounds the leaf and doesn't move away so high concentration of water particles outside leaf & inside so diffusion doesn't happen as quick

7. Good airflow

• Water vapour is swept away maintaining low concentration of water in the air outside lead so diffusion happens quickly

Importance of Transpiration:

• Nutrient Transport: Transpiration helps transport essential minerals and nutrients from the soil to different parts of the plant.
• Cooling: As water evaporates from the leaves, it helps cool the plant, preventing overheating in hot environments.
• Maintaining Turgor Pressure: Transpiration helps maintain turgor pressure (the pressure of the cell contents against the cell wall), which keeps the plant upright and supports growth.

Measuring Transpiration:

• Potometer: A potometer is a device used to measure the rate of transpiration by observing the uptake of water in a cut plant stem. By measuring the distance a bubble of air moves in the capillary tube, the rate of water uptake—and therefore transpiration—can be determined.