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Photosynthesis Lab

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Gabrielle Lyons

on 23 April 2010

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Transcript of Photosynthesis Lab

Photosynthesis Lab Lab Procedure Purpose and Hypothesis Photosynthesis Review: Key Concepts Conclusions How to Design an Experiment Lab Overview The rate of photosynthesis was measured for 5 cuvettes using DPIP (to replace NADP, which turns from blue to colorless as it is reduced. A spectrophotometer was then used to measure the percent transmittance of light of the cuvettes to measure the color change, thereby measuring the rate of photosynthesis by measuring the color change of DPIP. Purpose: to evaluate the effect of both chloroplasts and light on photosynthesis in spinach leaves
Hypothesis: Only the cuvette with both fresh, unboiled chloroplasts and light will display a change in transmittance, which represents photosynthesis Photosynthetic Pigments: absorb light energy and use it to provide energy to carry out photosynthesis. Include chlorophylls and carotenoids. Chlorophyll a participates directly in the light rxns by acting as the source of the electrons that flow through the ETC during PS.
The Chloroplast: Enclosed in a double membrane and contains both grana (where the light rxns occur) and stroma (where the Calvin Cycle occurs). The grana has layers of membrances called thylakoids, where PSI and PSII are located.
Photosystems: light harvesting centers in the thylakoid membrane, each containing a reaction center with cholorophyll a to absorb light. PS I absorbs light in the 700 nm range, so it is aka P700, and PS II absorbs light in the 680 nm range, so it is aka P680 Photosynthesis Review: Light Reactions in Noncylic Photophosphorylation 1. Light is absorbed by the photosystems (first PSII, then PSI) and electrons flow through the ETC (they are excited by the light and released, moving to a higher energy level)
2. The excited electrons are captured by a primary electron acceptor
3. Water is split apart, providing electrons to replace those lost in the photosystem, and releasing oxygen as a by-product, and providing protons for chemiosmosis
4. The Electrons power the ETC, as in cellular respiration, in order to power the production of ATP. In PS, this is called photophosphorylation
5. Chemiosmosis, the process that forms ATP occurs when the protons from water are pumped by the thylakoid membrane from the stroma into the thylakoid space, or lumen. ATP is formed when these protons diffuse down the gradient through ATP synthase channels, which adds a phosphate to ADP as it is powered.
6. NADP picks up the two protons released from water and becomes NADPH, an important input for the Calvin Cycle 5 cuvettes were used, each filled with a combination of water, a phosphate buffer, DPIP, and possibly a type of chloroplast
1. fresh chloroplasts/dark
2. fresh chloroplasts/light
3. boiled chloroplasts/dark
4. boiled chloroplasts/light
5. no chloroplasts
-These cuvettes were measured for their initial light transmittance, and then were placed in light (covered in aluminum foil if dark). After 5, 10, and 15 minutes, the light transmittance was measured again, noting any change Only cuvette 2 showed any change in light transmittance because photosynthesis could not occur without light and normal chloroplasts Guidelines: according to Barrons
1. Clear Hypothesis is Key
2. Must be a reasonable to carry out experiment that could work
3. Must have a control that stays constant throughout. This should be exactly like the experimental except without the single factor being tested for, or something left untreated.
4. Must have only one variable, so other variables must be controlled
5. Must have a large enough sample to draw a good conclusion
6. The experimental organisms all must be as similar as possible (same size, variety, etc.)
7. State the the experiment must be repeated!
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