Transpiration Investigation

When I conduct my experiment, I must take into account several conditions which must remain the same for all the test tubes at all times of the experiment in order to obtain more reliable results.

. Light

Plants transpire more rapidly in the light than in the dark. This is because light stimulates the opening of the stomata. Light also speeds up transpiration by warming the leaf.

2. Temperature

Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may transpire three times as fast as it does at 20°C.

3. Humidity

Transpiration is just another example of diffusion. Diffusion is the transfer of a substance from one environment to another; a substance will only diffuse from an environment that contains more of the substance to an environment that contains less. When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly.

4. Wind

When there is no breeze, the air surrounding a leaf becomes increasingly humid, which reduces the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air.

5. Soil water

A plant cannot continue to transpire rapidly if its water loss is not made up by replacement from the soil. When absorption of water by the roots fails to keep up with the rate of transpiration, the stomata close. This immediately reduces the rate of transpiration (as well as of photosynthesis). This can also cause the plant to wilt.

Below is some extra background information that I have used to assist me in my final planning.

Transpiration is the process of water loss from plants through stomata. In turn, more water is pulled through the plant from the roots. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. Stomata account for only 1 percent of a leaf's surface but 90 percent of the water transpired. In most plants, transpiration is controlled by the humidity of the air and the moisture content of the soil. Of the transpired water passing through a plant only 1 % is used in the growth process. Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated. Transpiration is a necessary process and uses about 90 percent of the water that enters a plant's roots. The other 10 percent is used in chemical reactions and in plant tissues. Some dry environment plants do have the ability to open and close their stomata. This adaptation is necessary to limit the loss of water from plant tissues. Without this adaptation these plants would not be able to survive under conditions of severe drought.

Results

Number of leaves

Weight before (g)

Weight After (g)

Difference (g)

Total Surface Area (cm²)

0

52.89

52.54

0.35

0

0

52.33

52.01

0.32

0

0

53.65

53.11

0.54

0

4

40.56

38.46

2.1

8.88

4

33.03

30.76

2.27

7.56

4

39.69

37.45

2.24

8.6

8

41.2

37.66

3.54

32.56

8

53.58

51.83

.75

20.64

8

53.63

50.73

2.9

41.68

2

42.55

38.61

3.94

44.28

2

42.19

38.01

4.18

45.12

2

41.29

37.65

3.64

48.0

This table shows the weight of the water before the 30-hour period and afterwards for each of the test tubes, this is compared to the total surface area of all the leaves on every stem. I calculated the averages for surface area and water loss.

Number of Leaves

Average surface area (cm²)

Average weight of water lost (g)

0

0

0.4

4

8.35

2.2

8

31.62

2.73

2

45.8

3.92

I have found that the larger the surface area, the more transpiration can take place. Also it can be found from these results that roughly 0.096652g of water will transpire for every cm² of a leaf in 30 hours. This can be used to work out how much water will transpire for any number of leaves or stems.

This graph shows that there is positive correlation between the surface area of all the leaves on a stem and the amount of transpiration that occurs when it is left for 30 hours. The trend line (shown in red) rises gradually in an arching shape; this suggests that if the graph were extended, the amount of transpiration would continue increasing with added leaves but eventually even out as the maximum transpiration limit had been reached.

Transpiration occurs mainly through the leaves while their stomata are open for the passage of CO2 and O2 during photosynthesis. The larger the surface area a leaf has, the more stomata there are and therefore more water can transpire. The reason the line seems to be steadily evening out is that the water from the test tube is being used up faster than it can transpire, this means that the rate of transpiration is decreasing and will eventually cease once all the water has left the tube.

Evaluation

All in all, my plan was a success. I was able to obtain useful evidence from my readings, as they were as accurate as possible given the constrictions of the conditions in which my experiment had to be conducted. There are few anomalies in my results because I ensured that the conditions in which my stems where kept remained the same for each stem. The stems were affected by the light, temperature, humidity, wind and amount of water but they were all affected equally by each of these factors so my results were still comparable. My experiments could be improved by eliminating fluctuation of these factors by creating an environment that would remain constant for the thirty-hour period.

The only major anomaly that I found in my results was one of my 8-leaf stems. The amount of water that transpired through this stem was much lower than the amount that transpired through the other 8-leaf stems and even some 4-leaf stems. I soon discovered that the reason for this was that the leaves were much smaller on this stem than the other stems and so the surface area was much smaller. Otherwise, all my results fit the pattern and my anomaly only adds to the evidence that clearly reveals the correlation between surface area and transpiration.

Transpiration Investigation - 26/04/2007