Transpiration

• TRANSPIRATION is caused by the EVAPORATION and DIFFUSION of water from the plant's surface, primarily the leaves.
• Most of the transpiration in a plant occurs through the STOMATA; small PORES found on the bottom of leaves.
• This process helps draw water up from the roots through the xylem and is a key part of the plant's WATER MANAGEMENT and NUTRIENT DISTRIBUTION

 

Transpiration rate, the movement of water within plants, is influenced by FOUR different factors:

 

1. LIGHT INTENSITY:

More light INCREASES transpiration. This is because the STOMATA OPEN UP in bright conditions to allow more gas exchange for photosynthesis. 

 

2.TEMPERATURE:

Higher temperatures INCREASE transpiration because they increase the energy of the water molecules, and makes them move FASTER. This means the rate of DIFFUSION and EVAPORATION of the water molecules out of the stomata increases.

 

3. AIR FLOW:

Good air circulation around a leaf INCREASES transpiration. This is because the air removes water vapour from the surface of the leaf and keeps the concentration of water outside lower than the inside. This increase in CONCENTRATION GRADIENT makes DIFFUSION faster.

 

4. HUMIDITY:

Higher humidity levels outside the leaf DECREASES transpiration. This is because it means there is a high water concentration OUTSIDE the leaf, which results in a LOW CONCENTRATION GRADIENT which results in slower DIFFUSION.

 

 

Measuring the Rate of Transpiration 

 

Setting Up the Experiment

• Use a POTOMETER to measure water uptake.
• Fill the potometer with water, ensuring no air bubbles are in the tube when inserting the plant.
• Mark the STARTING POSITION of an air bubble in the capillary tube.
• Begin the experiment by starting a stopwatch to measure time.
• Note the DISTANCE MOVED by the air bubble over a set period, such as an hour, to calculate the rate of water uptake.

You can estimate the rate of transpiration by measuring the how much water is taken up by a plant. This is because you can assume that water uptake by the plant is directly related to water loss by the leaves.

 

Reading the Results

The GREATER the distance that the air bubble moves in a period of time, the FASTER the rate of transpiration. Record this distance at regular intervals to calculate the rate.