These cells now contain little water in their sap vacuole. They are now flaccid.
The cells become plasmolysed when more water is diffused and the cytoplasm starts to pull away from the cell wall as the vacuole shrinks. The cells begin to wilt.
As the water reaches the leaves 1%-2% is used up during photosynthesis. The remaining water is diffused out if the stomata.
Stomata are openings normally found on the underside of a leaf. They allow water vapour and waste gases such as oxygen to be diffused out of the leaf.
The stomata are surrounded by two crescents shaped guard cells. Water passes into the guard cells by osmosis. This makes them bend so the stomata open.
The guard cells open during the day in the presence of light. They close at night and also in dry conditions (when they are flaccid). This is because water loss in transpiration is not being replaced by water absorbed by the roots. The stomata close to reduce the rate of transpiration.
When the guard cells are open they are turgid. The small percentage used up in photosynthesis during the day is not used up during the night because the plant photosynthesises during the day and respires at night.
The water available from the soils can vary with the different types of soil for example sand retains little water and drains very easily. Clay retains a great deal of water but has a very high wilting point because tiny pores in the soil exert a lot of suction.
It is important that gravity and capillary forces act upon the water. If they didn’t water would drain away and no plants would grow. The soil will turn to dust and erode away.
Aim:
In this investigation I will be seeking to find out how the wind speed affects the rate of transpiration.
Prediction:
I predict that the rate of transpiration will increase when the fan is closer to the plant. This is because when the fan is closer it has a greater wind speed. With a greater wind speed more water vapour can be blown away at a greater speed. This means the vapour pressure around the plant decrease allowing more water vapour to be diffused out of the stomata.
As I explained in my factors the plant can only diffuse water trough the stomata if the leaf cells contain more vapour pressure then the air around the plant.
If the air is humid the rate of transpiration decreases rapidly. This is because the process of osmosis cannot be carried out properly. The rate of transpiration slows down then stops.
My theory is supported by a similar experiment carried out by another student in our class. Her procedure was identical except for the fact that she was not distancing the plant from the fan she was changing the speeds on the fan. She had three speeds. She found that the rate of transpiration increased as the speeds did.
Apparatus
Geranium plant.
Rubber tubing.
Glass tube.
Capillary tube.
A beaker of water.
Fan.
Ruler.
Stopwatch
I will be using a geranium plant to see how the rate of transpiration alters. The rubber tubing is there so no water loss can occur between the glass tube and plant shoot, as this will affect the water uptake. The glass tube contains a capillary tube, which enables the experiment to take place faster. The capillary tube is small and thin, it allows the bubble to move along faster. The beaker is where the source of water is. The ruler is for measuring the distance travelled by the bubble. The stopwatch is to time the experiment.
The whole apparatus apart from the stopwatch will be fitted together makes a potometer.
Fair test
To conduct this experiment successfully I will only have one variable, the distance of the fan. I will be doing three sets of trials all using the same apparatus. By repeating the experiment I will be able to collect reliable results. As other people in the class will be working with fans I shall have to make sure their fans will not affect my plants rate of transpiration.
Reliable results
To obtain reliable results I will repeat the experiment three times under the same conditions. By being able to view three sets of results I shall be able to circle out any anomalous results.
My geranium will only be able to stay healthy for a few days. I will try to do the experiment efficiently to gather accurate results.
While doing the experiment I will need to take a few precautions. When I am placing the geranium shoot into the rubber tubing I will try not to bruise the xylem cells, as this will affect the plants uptake of water. If that happens I cannot keep the uptake of water consistent.
What to measure
It is not easy to measure the rate of transpiration but I can use a potometer to measure the rate of water uptake. I know that the amount of water loss is less then the water taken up by the roots as some of the water is used for photosynthesis.
I will move the fan 20cm at a time until the fan is 80cm away. I chose these measurements because earlier in my preliminary work I moved the fan 10cm at a time. I found out that this distance was too short because there was not much difference displayed between 10cm and 20cm, 20cm and 30cm and so on. Now I am moving the fan 20cm at a time, as this will show much clearer results.
The air bubble in the capillary tube will be measured for 3 minutes for each fan distance. At first I decided upon 30 seconds but this did not show clear differences in the results.
I was hoping to do 5 sets of results but this will take to much time and the plant will become unhealthy.
I will also measure the speed and volume of water the bubble has to show clearly how the rate of transpiration is affected by the wind speed.
Results table
Procedure
First I shall fill the capillary tube by submerging it in water.
Next I will cut the end of geranium soot under water.
I will attach the shoot to rubber tubing connecting the plant to the capillary tube.
I will have to attach a ruler near the glass tube to measure the distance travelled by the air bubble.
To make an air bubble I shall have to take the glass tube out of water and rube the end to remove excess water. When I place the tube in water I shall be able to view an air bubble.
I will set the stopwatch and after 2 minutes I will off it. I will measure with the ruler the distance travelled by the bubble during that time.
I will continue this until the experiment is over.
Analysis
The pattern, which appeared on my graph, shows that when you distance the fan further from the plant the rate of transpiration decreases.
When the fan was 20cm away from the plant the distance moved by the bubble was 44mm and the uptake of water was 8.6ml. The distance travelled by the air bubble was 35mm when the fan was 40cm away from the plant. The uptake of water was 6.9ml. This shows clearly how the wind speed affects the rate of transpiration.
The reason for the rate of transpiration altering is because of the change in wind speed.
(In my experiment differences of speed is created by moving the fan certain distance
From the plant.)
With an increased speed more water vapour can be blown away. This means the vapour pressure in the air decreases more rapidly allowing water vapour to be diffused faster from the stomata. This increases the rate of transpiration. This is because the plant transpires slowly when the vapour pressure in the air is equal or greater then the leaf cells due to the process of osmosis not being carried out properly. Osmosis works when the leaf cells have more vapour pressure then the air. The cells with a higher concentration of water diffuse water trough the cell wall to the cells with low concentrations of water.
If the vapour pressure in the air is gradually decreasing, the plant can only transpire slowly at the rate limited by the pressure around it.
My results support my original prediction of how the rate of transpiration increases when the fan is closer to the plant. At a fan distance of 60cm the distance travelled by the bubble was 25mm and at 80cm the bubble had travelled 18mm. My graph also supports my original theory. With a greater wind speeds more water vapour can be blow away, decreasing the pressure in the air. This means osmosis can be carried out quicker, increasing the rate of transpiration.
Results table
The calculation for the volume of water was
0.25*0.25*3.142*Average result.
The radius of the capillary tube was 0.25.
Evaluation
Accuracy of results
My results were considerably accurate for my investigation. Although the results show clearly how the wind speed affects the rate of transpiration, there were to many variables I could not control.
Reliability of results.
The weather is an environmental factor, there is no way we can control it. The weather can affect my investigation by supplying extra heat, light and wind.
The heat has the affect of evaporating the water from the leaves causing the plant to transpire more. The light stimulates the expansion of the stomata and the wind clears away outside vapour pressure.
The weather is not consistent and in the three days in which I carried out my investigation it varied from hot to cold and windy to humid.
There is one floor in my procedure. I should have conducted the experiment in the plants natural habitat. Soil was missing from my experiment. I explained in my background knowledge how soil could affect the uptake of water in a plant. I didn’t include soil in my procedure because it will be hard to measure the uptake of water.
On the third trial of the investigation I found an anomalous result. As it was not in the average column it did not show up on my graph and so all my points are near to the line of best fit. The result was collected when I was distancing the plant 80cm away from the fan.
Results table
You can see it is an anomalous result because the percentage change between the 2nd and 3rd trial is 87.5% and the percentage change between 1st and 3rd is 82.4.
These are big changes compared to the results I got for the trial on 20cm.
The difference between 1 and 2 is 4.5%, for 2 and 3 it is 4.3%.
I don’t think I had enough results to draw an accurate conclusion. This is because I had only done 3 sets of results. To obtain more accurate results I need to have repeated the experiment several more times to approach nearer to the accurate results.
Reliability of method.
My method was unreliable because it took to much time to carry out. The weather and the health of my geranium plant affected my results. The weather was never consistent; it may be hot one day and cold the next. If the xylem tubes of the plant were not in working order it would affect the rate of water uptake.
I should have included a reservoir near the end of the capillary tube. When the experiment is finished I wouldn’t have needed to wait for the air bubble to travel all the way to the stem of the plant. With the reservoir I can use a syringe to push water out of the capillary tube. The water will push the air bubble out of the capillary tube in a matter of seconds.
To obtain an accurate result on the topic I should have looked at a wider range of plants and environments. I could look at different species of plants for example a cactus. A cactus takes up a lot of water trough it’s roots but has a small percentage of water loss. The cactuses leaves have a small surface area because they cannot afford to loss much water as it hardly rains in the desert. I could also look at plants that live in water. These are some questions I could ask. The water vapour outside the plant cell is greater so how do they transpire? Does heat and light have much affects on the plants that live deep on the seabed? Could it be that they do not transpire or photosynthesis?