Transpiration Coursework

-Planning

I plan on conducting an experiment to find out whether the surface area and number of leaves on an individual stem has any effect on the change of weight of the leaves.

Hypothesis-

I predict that the leaves will all become lighter, and the more leaves on the stem, the more weight will be lost. I predict this because the water is taken back into the leaves, and is lost through the tiny holes in the leaves called stomata. The stems with more leaves on them will lose more weight, as there are more holes for the water to be lost through, also, the leave with the largest surface area will lose the most weight for the same reason.

Apparatus-

Test- tubes

Privet bush cuttings

Beaker

Balance Scales

Water- 15 ml

Oil

Measurements-

I will use a balance to measure the new weight of each test- tube. I will measure the specific amount of water being poured into each test-tube, and I will measure the surface area of an average sized leaf on each stem. I will do this by drawing round the leaf on squared paper, and then counting the squares. The weight will me weighed in grams (g), the surface area will be measured in cm squares, and the weight lost will be in grams (g).

Fair Test-

I will make this a fair test by; keeping the amount of water at a constant amount of 15ml, with 3 drops of oil on top so that the water does not directly evaporate out of the test-tube. The test-tube rack will be always in the same room at all times, therefore in the same temperature and conditions.

The amount of water in each test-tube will always be the same because the more water there is, the more water can be absorbed by the stem, so the weight could take longer to ...

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Fair Test-

I will make this a fair test by; keeping the amount of water at a constant amount of 15ml, with 3 drops of oil on top so that the water does not directly evaporate out of the test-tube. The test-tube rack will be always in the same room at all times, therefore in the same temperature and conditions.

The amount of water in each test-tube will always be the same because the more water there is, the more water can be absorbed by the stem, so the weight could take longer to decrease as there is more water to absorb into the stomata. The experiment will be kept in the same room, as temperature has an effect on the rate of transpiration. Transpiration always works best in hot, dry conditions.

Variable-

I have chosen to use the amount of leaves on each stem as my variable. The surface area is also varied, but that is not a controlled variable. This enables me to find out whether the amount of leaves and surface area has a positive or negative effect on the transpiration rate of the leaves.

Method-

I will use four test tubes, each with 6, 8, 10, and 12 leaves inside. In each test tube I will put 15ml of water, with roughly 3 drops of oil on top. Each test tube will be placed in a test tube rack, which will then be placed in a room. All of the test-tubes will always be kept together, so that no test-tube has any advantages or disadvantages over each other.

I will weigh the starting weights (day 0) on the balance scales, and record this. I will then weigh all the leaves for 5 days. I will record and analyse my results.

Diagram- (attached is a general diagram of how Transpiration occurs in plants)-

Results-

Day No. Leaves Surface Area Weight _ Weight Lost

N.B- An average sized leaf from each test tube was taken for the surface area measurements.

Conclusion-

As I predicted, the leaves decrease in weight each day. The test tube with more leaves on the stem does decrease more than the others. This is because, as the water is taken up the stem, the water reaches the stomata and then is evaporated away from the leave causing weight loss. The more leaves, the more stomata’s for the water to be lost out of. The surface area of the leaves in each test tube was not a significant amount more or less than each other.

There-for, I could not judge whether the surface area was having a significant impact on the results, although I know scientifically that the larger surface area would enhance the transpiration.

Overall, the more leaves there were the more successful transpiration was. If surface area were my controlled variable, I would find that the larger surface areas lost more weight than the smaller surface areas. I think that I have obtained enough evidence to support the idea of transpiration, and my experiment was successful and my prediction was correct.

Evaluation-

Originally, I conducted the experiment with 5 test tubes, but one test tube was lost during the experiment so I adapted my results to cover 4 stems. If I were to repeat the experiment, I would use 5 test tubes, and monitor them more closely so that one would not be misplaced and go missing. I think that my experiment went well and I did not come across any anomalous results as I expected. I could extend this investigation by monitoring more aspects of the investigation, although this would lengthen the experiment a lot. I could measure the temperature of the environment the leaves are being tested in, as it is known that temperature and the atmosphere have a great effect on the rate of transpiration. I could also vary the types of cuttings used, as the leaves used in my particular experiment were privet cuttings. I could see if the different types of leaves had different amounts of holes or had different rates in transpiration. I could have tried putting the cuttings in different solutions, instead of tap water; I could have varied temperatures or by using salt solutions. By doing this, I would have obtained a much wider variety of results, which would give me a deeper insight to the experiment. I could have varied the brightness of the environment that each test-tube was placed in, for example; light, dark, etc.

I could have obtained a larger variety of results by doing the experiment for a longer period of time, which would show a more of a decreasing in weight. I could have also used more than four test tubes, as four test-tubes gave me a slightly limited group of results, although they were sufficient.