Biology Research for Photosynthesis

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Paras Gaba
AP Biology, Block 1
3 February, 2013
Mrs. Killough

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. 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...
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