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CBL Interfacing

Photosynthesis In Isolated Chloroplasts


Suggestions For Teacher

Length of Lab: 2 (40-45) minute periods.

Safety Precautions: The lab involves working with chemicals. Goggles should be worn at all times.

1. Remind students to fully insert the I/O cable in the CBL and TI 82.

2. Timing is important in this lab. Students should organize themselves to insure that they are able to take readings at the proper time.

3. Accuracy of measurements is also crucial. Go over proper pipetting technique.

4. It is important to place a heat sink between the samples and the light. A large flask, beaker or even a small fish tank filled with water will work.


Sample Data

Plot


Answers To Questions

1) For each sample, describe the relationship between absorbance and time? In which sample did the absorbance drop most dramatically?

The cuvettes with the boiled chloroplasts and with the chloroplasts kept in the dark showed little change in absorbance. The chloroplasts kept in the light showed a drop in absorbance.

2) What is the effect of darkness on the reduction of DPIP?

There is very little reduction of DPIP by chloroplasts kept in the dark.

3) What is the effect of boiling the chloroplast on the reduction of DPIP?

There is very little reduction of DPIP by boiled chloroplasts.

4) What was the initial rate of DPIP reduction by the unboiled chloroplasts that were incubated in the light?

At first there is a linear reduction (indicated by the negative slope) of DPIP.

5) How did the rate vary during the experiment's time course?

The curve began to level off, indicating that the rate of reduction of DPIP was tapering off.

6) There are two major products of photosynthesis-water and organic substances such as glucose. How would the presence of DPIP affect the production of oxygen during the light reaction? How would the presence of DPIP affect the production of organic product during the dark reaction? Explain.

Using an artificial electron acceptor will allow for the production of oxygen during the course of the light reaction. However, without the formation of NADPH2, the dark reaction will not occur and organic product will not form.

7) What role did another artificial electron acceptor, ferricyanide play in elucidating the process of photosynthesis?

The phenomena described in question #6 was the basis for separating the light reaction from the dark reaction. Hill used ferricyanide, however, as an artificial electron acceptor. He is credited with isolating the light reaction.

8) If time permits, design and set up an experiment comparing how the wavelength of light would affect reduction of DPIP. Analyze the slopes and discuss your results.

In such an experiment several cuvettes are set up similarly to the one kept in the light in the experiment the students just did. However, the use lights of different wavelengths. The data for each cuvette is plotted and compared.

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