Key variables
Temperature
The plant will be placed indoors in room temperature, which is controlled by central heating. The high temperature will dry up the air and the outside of the leaves and speed up the transpiration process.
Transpiration in Plants
Experiment
Key variables (cont)
Light
The plant will be in a room with artificial light, which will cause the stomata to open and speed up the transpiration process.
Wind
Place the plant in normal room temperature then place the plant in a current of air form an electric fan. This will represent a windy environment and confirm if wind affects the rate of transpiration.
Time and Distance
Time the rates of transpiration over a distance of 15cm with a stopwatch. Compare the rate of transpiration for each circumstance to check if there is any change.
List of Apparatus
- 1 beaker
- 1 pair of scissors
- 1 leafy shoot
- Vaseline
- 1 rubber stopper
- 1 glass tube
- 1 clamp stand
- 2 clamps
- 2 bosses
- Sink full of water
- 1 stopwatch
- 1 hairdryer
- 1 ruler
Transpiration in Plants
Experiment
Method
- Place the plant in the water and cut the stem at a slant to give maximum surface area.
- Place the rubber stopper in the tube
- Place the plant stem in the rubber stopper ensuring there are no air bubbles in the tube
- Immerse the beaker in the water and place the tube in the beaker while still immersed
- Carefully place the beaker on the desktop
- Smear Vaseline around the rubber stopper and plant stem
- Clamp the plant and the glass tube to the clamp stand to ensure the materials are fixed in place.
- Fix the ruler to glass tube
- Carefully remove the tube from the water
- Dab the tube with a paper towel to create an air bubble
- Time how long it takes the air bubble to travel 15 cm
- Repeat experiment 2 more tomes
- Repeat whilst adding hot air from the hairdryer
The equipment is put together to make a potometer. The reason for placing the plant stem in the water before inserting in the tube is to prevent any air bubbles getting in. Extra care should be taken not to wet the leaves on the plant as this could effect the transpiration rate due to the high concentration of water molecules that are on the outside of the leaves
Vaseline is smeared on the stem and at each opening the opening of the tube to prevent any air or water escaping.
When the apparatus is assembled and the air bubble created it will start to move up the tube following the transpiration stream in the stem. The diffusion of water through the stomata will pull the water molecules, which cling together by capillary action towards the leaves travelling in the xylem vessels. The air bubble will move up the capillary tube at the same rate that the water is transpiring in the plant.
The addition of the air stream to the plant will decrease the concentration of water molecules in the atmosphere. This will cause the molecules in the leaves to evaporate and diffuse more quickly thus sucking the water from the stem up the transpiration stream at a quicker rate, therefore increasing the transpiration rate. This rate of the air bubble will also decrease in the capillary tube.
Transpiration in Plants
Experiment
Results
- The rate of respiration in normal conditions was 2cm per minute
- The rate of respiration with the addition of the air stream was 2.5cm per minute.
- These results justify the hypothesis and prove that the rate of transpiration increases in a plant in a windy environment.
The rate increased by 0.5cm per minute. This is because although the conditions were fairly dry due to the plant being in a dry heated environment the addition of the air stream blew any water molecules away. The disappearance of the molecules reduced the concentration on the outside of the leaves, which caused more water to diffuse through the stomata. This speeded up the evaporation process in the leaves.
Because the water was evaporating faster through the leaves then the capillary action also became quicker causing the molecules to travel through the stem into the xylem at a faster rate. The airflow was held until the air bubble reached the desired point, which increased the whole transpiration process, which explains why the air bubble was moving quicker in the potometer
The temperature and dry conditions of the inside environment would have meant less concentration of water molecules in the air than in an outside environment thus speeding up the whole transpiration process in both experiments.
The plant was dying which means the initial transpiration rate was slower than in a normal living plant. The rate is slower in a dying plant because some of the components in the leaves and stems that no longer work do not assist with the transpiration and therefore it slows down.
It was difficult to remove all the air bubbles from the capillary tube when first inserting the stem and at the end of each testing. This could have affected the rate of transpiration.
Parts of the plant had been broken off leaving holes in the stem. Although Vaseline was applied to holes to block them water may have escaped through them.
Ideally the experiment should have been conducted three times to get an average result for both conditions, but time was limited due to the process taking longer because of the dying plant.
Transpiration in Plants
Experiment
The experiment could be improved by using a fresh living leafy shoot instead of one that was dying. The transpiration rate would on the whole be quicker than the previous experiment thus allowing time to conduct it three times for both circumstances and recording more results.
A hairdryer would be a quicker and more controlled method for an air stream supply, which would also allow more time to repeat the experiment.
A potometer with a tap attached would assist in removing unwanted air bubbles and a capillary tube with a scale would ensure more accurate results.
Without the logistical problems there would have been more time to carry out repetitions of the experiment and record more results to be analysed.
An experiment testing the change in transpiration rate for different environmental conditions could be carried out as follows:
Humidity
- Cover the plant with a plastic bag.
Surface area
- Smear the top of the leaves with Vaseline and then the bottom of the leaves, reducing the surface area where transpiration takes place.
- Remove some of the leaves from the plant, reducing the surface area
Even though the plant tested was dying, which induced a slower rate of transpiration than would be expected from a normal living plant and more repetitions could have been tested, the experiment satisfactorily proved that the rate of transpiration increases in a windy environment.
