Investigating the Effect of Light Intensity on the Size of a Plantain Leaf

Investigating the Effect of Light Intensity on the Size of a Plantain Leaf
Title: To investigate the effect of light intensity on the size of a plantain leaf. Hypothesis: I predict that the size of the plantain leaves would increase as the light intensity decreases. Therefore, plantain leaves found in the shade will have larger surface areas than leaves found in an open area. Theory: Sunlight is an essential factor need to complete the process of photosynthesis. Photosynthesis consists of the following equation: Sun light Carbon dioxide + Water ====> Glucose + Oxygen Chlorophyll Chlorophyll is a substance found in chloroplasts, found in the cells of leaves. They are used to produce glucose which is used as plant food and growing materials (e.g. cellulose).A leaf which is exposed to plenty of light will have sufficient amounts of food and will not need an excessive amount of chlorophyll. This enables the leaf to have a small surface area
It is also necessary for leaves in areas of high light intensity, and thus high temperature, to have small leaves to reduce the amount of transpiration. The heat will cause water to evaporate a lot faster. Leaves in shaded areas will need a large surface area full of chlorophyll to collect as much sun light as possible; essential for survival. These leaves will also have no threat of excessive transpiration because the temperature in the shaded area will be lower and the humidity probably higher. Transpiration is the removal (evaporation) of water from a plant through the stomata in the leaves; this water is removed in a cycle due to the active uptake from the roots. Transpiration involves osmosis; which is the diffusion of water from a high concentration to a lower concentration through a partially permeable membrane, until both the concentrations are equally saturated. All these factors i.e. transpiration and photosynthesis, come together to confirm my hypothesis. To support my hypothesis further, I did a pilot study in a meadow in which I studied the population of certain plant species in areas of different light intensities. I learned that different plants need different environmental factors to grow well. The leaves in the shade were larger than those in the open field. Expected Results: As the light intensity increases, the surface area of the leaves decreases. This sketch shows a line of best fit; in real life it probably wouldnÂ?t be so accurate. [image] Variables: The independent variable in my investigation is the light intensity in the area we are investigating. The other independent variables in the experiment have to be kept constant. If they are not kept constant, then it will not be a fair investigation. The independent variables I am keeping the same in this investigation are: 1. Temperature Â? change in temperature might affect the rate of transpiration. 2. Humidity of the field: Â? this will also affect the rate of transpiration as it will determine the concentration gradient during osmosis from the stomata. 3. Wind speed Â? this will affect the humidity of an area. 4. Moisture level Â? this is an important factor in photosynthesis. If there is a variation in the moisture levels then the level of transpiration will vary, making the investigation unfair. 5. Amount of human and animal activities ? this will always have an effect on the environment and should be prevented as much as possible. The dependent variable in this investigation is the change in the leaf surface area. Apparatus List:
A small quadrat 25cm x 25cm
Papers Â? lined and graph paper
Pencils
Sun light meter
Humidity and Temperature meter
Skill area O: Obtaining evidence Procedure: 1. Get together all the apparatus listed above and pick out the site for your experiment. Prepare a table to record the data collected. 2. Look around and gauge which areas are shaded and in full light. 3. Throw the quadrat somewhere as randomly as possible towards a shaded area. If there are no plantain leaves in the quadrat, continue to throw it until you get some. 4. When you have found a good plantain leaf sample, measure the light intensity, humidity and temperature over the quadrat. 5. Take a leaf sample from the quadrat and trace it unto some graph paper. Also record the data collected in step 4 on your results table. 6. Repeat steps 3 Â? 5 in different light intensities i.e. the shade, full light and moderately lit areas. 7. Calculate the surface areas of the leaves using the squares on the graph paper. You will have to estimate the surface area and round them to the nearest unit. (1.s.f.). 8. Record all your data into the table you previously prepared. Precautions:
Make sure you stand clear of the path of the quadrat being thrown.
Avoid throwing it to close to the river too.
When using the sunlight meter, make sure there are no objects
obstructing the reading i.e. stand back from the meter.
To make the test fair, throwing the quadrat should be a completely
random process. This can be achieved by closing ones eyes when
throwing the quadrat, or to spin around in a circle to confuse oneself
of bearings or position.
To also make the test fair, make sure the same person carries out
each measurement i.e. the same person measures the light intensity as
their opinion will always be the same.
Table: Plantain Leaves Light Intensity (klux) Humidity (%) Temperature (ËšC) Area where leaf was found Surface Area (cm2) 1 30 75 16.8 Under tree 45 2 33 73 15.4 Under tree 37 3 32 74 15.6 Under tree 32 4 30 75 16.1 Under tree 30 5 45 62 20.2 Under tree 19 6 40 75 15.2 Under tree 18 7 32 74 15.6 Under tree 15 8 36 76 15.7 Under tree 10 9 60 76 16.0 Medium open 34 10 43 75 16.6 Medium open 31 11 40 75 16.3 Medium open 23 12 52 74 15.8 Medium open 17 13 44 74 15.6 Medium open 13 14 45 75 14.9 Medium open 13 15 41 75 18.3 Medium open 12 16 40 74 16.0 Medium open 10 17 51 72 16.4 Full open 18 18 51 74 16.2 Full open 17 19 42 76 17.3 Full open 8 20 58 77 15.8 Full open 7 21 30 76 15.1 Full open 7 22 57 77 15.8 Full open 6 23 54 76 15.0 Full open 5 Graph: [image][image] Skill area A: Analysing evidence and drawing conclusions On my graph I can see a definite pattern. In each of the 3 columns, showing the locations of the leaf samples, the points on the scatter graph all moved down in descending order as the light intensity increased. The points in the first column, Â?Under the treeÂ?; rose to the highest point i.e. highest surface area which was 45 cm2. The beginning of each Â?locationalÂ? column always has the highest surface area point. This suggests that the specified areas will be overlapping each other; they are not clean cut at all. The pattern on my graph fits my hypothesis exactly. It shows that as the light intensity increases, the size of the leaves decreases. The temperature on the day we did our experiment was not very high, but I could still see the clear difference between the leaf sizes. Transpiration was not encouraged by the low temperature, and also the humidity was very high which would have reduced the osmosis gradient and slowed down transpiration. Skill area E: Evaluation I think my investigation was not as great as I would have liked. I admit that my lack of enthusiasm at the beginning might have contributed to it, but also because the working conditions we had were not great. As you can see from the table of results, it was a very humid environment, it was cold and cloudy; all these were not exactly the right conditions to get good results. However, we did get adequate results that substantiated my hypothesis. My investigation could have been improved in many ways, most of all if we had the optimal weather conditions we need. To have made it a fair test, and made sure all the other independent variables remained constant; I could have used a controlled environment like a greenhouse. With a larger area to investigate with fuller trees and more working time; I could have collected more samples. I would have used this to make the graph my informative and specific. Also, testing other plant species other than the plantain would have been useful e.g. ribwort, dandelions. To further my experiment I actually investigated another plant species growing with the plantain leaves, dandelions. I carried out the method stated above to collect my dandelion samples and recorded my results in the table below. Dandelion Plants Light Intensity (klux) Humidity (%) Temperature (ËšC) Surface Area of leaves (cm2) 1 55 75 15.9 39 2 48 74 15.5 20 3 46 76 15.9 19 4 49 75 16.5 13 5 50 76 16 12 6 56 77 15.4 12 [image][image] This table and graph also confirm that my initial hypothesis was correct.

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