Shape of Leaf Disks and Photosynthesis Research Question: Does the shape of the leaf disks affect the rate of photosynthesis if the surface area of the leaves are kept the same? Purpose: Through this experiment, I seek to answer whether the shape of leaf disk affects the rate of photosynthesis to find out which leaves are more efficient at utilizing free energy from the environment. Specifically, if there is a significant difference in the rise time (p>.05) of circular leaf disks and rectangular leaf disks. Hypothesis: Knowing that the rate of photosynthesis is governed directly by the limiting factor of free energy (sunlight, water, carbon dioxide) and knowing that differences in leaf disks shape doesn’t necessarily impact these factors, I predict that the shape of the leaf disks doesn’t make a difference if the surface area is kept constant and equal. Independent Variable: In this experiment, I’m going to use the shape of the leaf disk as the independent variable. I’m going to employ square shaped leaf disks in order to check if there is a difference in the rate of photosynthesis from the control. Dependent Variable: In this experiment, my dependent variable is going to be the time it takes for the leaf disks to rise up to the top, which is going to be tested by different shaped leaf disks.
Controlled Variable: The circular shaped leaf disks are going to be my control for this experiment. We also control how much sodium bicarbonate is added, the amount of water that is present, and the amount of sunlight that each disk receives. Possible Confounding Variable: Because the leaf disks are small and move frequently in the beaker while under the lamp, we can’t possibly govern the effect of photosynthesis of one leaf disk to another. Also, different placement of the leaf disks could yield different time of rise. Background Research: Many studies claim that the shape and size of a leaf affects the rate of photosynthesis. The size and shape of leaves is an example of a compromise between leaf energy exchange, leaf temperature, and photosynthesis. “Leaves growing in sunny environments are smaller and more deeply lobed than leaves growing in shaded environments.
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Abstract This study was undertaken to determine the relationship of different wavelengths of light and the rate of photosynthesis in spinach leafs. The rate of photosynthesis was measured every five min under light colors of white, green, red, blue and yellow under a light intensity of 2000 lux. The rate of photosynthesis was measured by the spinach disk method in which we replaced the air from ...
Leafy plants growing in the hot, arid environment of deserts or cold arctic and alpine environments have small leaves. In part, this is related to the influence of leaf dimension on leaf boundary layer resistance and the efficiency with which heat and moisture are transported away from a leaf”. (Parkhurst and Loucks 1972; Givnish and Vermeij 1976; Woodward 1993a).
Even though these findings are very thorough, they only are valid mostly when there is also a surface area or size change. Photosynthesis: Fuels ecosystems and replenishes the Earth’s atmosphere with oxygen. Like all enzyme-driven reactions, the rate of photosynthesis can be measured by either the disappearance of substrate or the accumulation of product (or by-products).
6CO2 + 6H2O + Sun –> C6H12O6 + 6O2
The yield of the 6 oxygen gas molecules is the factor that will increase the rise of the leaf disks to the top so therefore, determine the rate of photosynthesis. Material:
* Baking soda (sodium bicarbonate)
* Liquid soap (approximately 5 mL of
* dishwashing soap in 250 mL of water)
* 2 plastic syringes without needle (10 mL or larger)
* Living leaves
* Hole punch and scissors
* 2 clear beakers
* Phone timer
* Light source
Safety: There are many safety hazards to be cautious about during the course of this experiment. We are using old bulbs and they can be overheated and fuse out so we have to stand away from the light source. We are also dealing with glass ware so caution and careful dealing is required there. But the major concern arises from people walking around aisles so bags have to be tucked in the desks and we have to be mindful of the chairs and tread lightly. Another reason to worry is that Procedure:
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1. Make a .2% solution of sodium bicarbonate and water. (Make 200 mL solution so plenty for both groups)
2. Add a drop of soap into the solution.
3. Split the solution into two groups.
4. Ready the lights on a steady height but don’t turn the lights on.
5. Cut 15 circular leaf disks and measure the area and then cut out 15 square shape leaf disks with the same area. 6.
Cut 15 circular leaf disks and measure the area and then cut out 15 square shape leaf disks with the same area. 7. Draw the gases out of the spongy mesophyll tissue and infiltrate the circular leaves with the sodium bicarbonate solution, which acts as a wetting agent between the mesophyll. 8. Put the solution under the lamp and turn the lamp and timer on and record the time when each leaf disks rises to the surface. 9. After each circular leaf disk has risen to the surface and been timed, add the square leaf disk mixed solution under the lamp and record the time when each disk rises to the top. 10. Then we add the disks in a rectangular disks and do the same process as above. Data:
Data Table 1: Time of Rise in Circular
Leaf Disks
Trial| Time for Circular Leaf Disk to Rise (seconds)|
1| 331|
2| 332|
3| 341|
4| 342|
5| 356|
6| 357|
7| 360|
8| 385|
9| 420|
10| 452|
Mean| 367.6|
Median| 356.5|
Standard Deviation| 40.06|
Data Table 2: Time of Rise
in Rectangular Shaped Disks
Trial| Time for Rectangular Leaf Disk to Rise (seconds)|
1| 380|
2| 438|
3| 462|
4| 466|
5| 478|
6| 484|
7| 494|
8| 498|
9| 445|
10| 423|
Mean| 456.8|
Median| 481|
Standard Deviation| 36.48|
Graph:
Observational Comparison between Data 1 and Data 2: There is an obvious difference between the time it takes for the circular leaf disks to rise and the rectangular leaf disk to rise. We can see that the mean and median for Data 2 (rectangular) is much higher than Data 1 (circular).
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Since right now I am only making an observation, it is safer to follow the median because the mean is easily suspect to bias and outliers. My hypothesis seems to be invalid because there is much higher median time of rise for rectangular leaf disks than circular leaf disks. This conclusion is not proven yet and a 2-sample T test would have to be conducted to see if there is significant difference in the rates of photosynthesis between circular leaf disks and rectangular.
Calculations:
2-sample T test
µ1: The mean rise time of circular leaf disks.
µ2: The mean rise time of rectangular leaf disks.
H0: µ1 = µ2
Ha: µ1 ≠ µ2
Conditions:
* Random sample of circular leaf disk and rectangular leaf disks not give. Our results may be suspect to bias. * Independence is reasonable because the rise time of one leaf disk shouldn’t affect other leaf disks. * Box plot is symmetric enough to continue.
t=(Differences of means –Parameter)/ Standard Deviation of Statistic Differences of means= (µ1-µ2) = 367.6-456.8 = -89.2
Parameter=0
standard error of difference = sqroot[(40.06/10)-(36.48/10)] = 17.652 Intermediate values used in calculations:
t = 5.2659 .000182
df = 17
standard error of difference = 17.652
P value and statistical significance:
-The two-tailed P value is less than 0.0001
-By conventional criteria, this difference is considered to be extremely significant
Test findings: We have to reject the null hypothesis (µ1 = µ2) because our P-Value (.000182) is significantly lower than the alpha (.05).
This test indicates that rectangular shaped leaf disks require a higher time to rise than the circular leaf disks, showing that there is a slower rate of photosynthesis in rectangular disks. Conclusion: My hypothesis was that differences in leaf disks shape doesn’t necessarily impact the rate of photosynthesis. This hypothesis is rejected by or data and 2-sample t test. The mean and median respectively for Data 1 (circular leaf disks) were 367.6, and 356.5. The mean and median respectively, for Data 2 (rectangular leaf disks) were, 456.8 and 481.The central time it takes for a rectangular leaf disks is much higher than the central time it takes for a circular leaf disks to rise. I also ran a 2 –sample t test which concluded with a surprising p-value of .00083.
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These statistics show that the rate of photosynthesis is higher in circular leaf disks than rectangular leaf disks. But there are many errors and limitations to our experiments that can be improved and fixed. Errors/Limitation: Our test indicated that there is a much faster rate of photosynthesis is circular leaf disks compared to rectangular leaf disks with a 2-sample t test. But our conditions for the 2-sample t test weren’t fully satisfied because there was no random sample given to ensure no bias and independence could be flawed since all leaf disk trials were run in the same beaker at the same time. Another possible error that could be the reason to our results is that circular leaf disks have more fluid buoyancy and rise easier than rectangular shaped leaf disks. Also, we didn’t test multiple shapes due to a lack of time so we don’t know about the rate of photosynthesis of other shaped leaf disks. Improvements: We can improve our test if we ran a lot more samples (about 50) to satisfy the condition for large samples, then we could randomly select using a number generator leaf disks to use in the experiment to satisfy the first condition. We should also test multiple different shapes of leaf disks and compare them to circular leaf disks to test their rate of photosynthesis.
