Lab Photosynthesis

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The following movie represents the experimental setup for the

light intensity experiment.

Slide 9

Exercise #6 PHOTOSYNTHESIS

PROCEDURE (continued)

75 cm - Move the lamp so it is 75 cm away from the experimental tubes and place the heat

filter half way between the lamp and tubes. Wait 5 minutes for equilibration. Adjust

the fluids in the pipettes so that they are at the 0.2 ml mark and recalibrate only when

changing the distance to the light source. Record the position of the fluid in the

pipettes at 2 minute intervals for 10 minutes.

50 cm - Move the lamp forward so it is 50 cm away from the experimental tubes and again place

the heat filter half way between the lamp and experimental tubes. Wait 5 minutes for

equilibration and adjust the fluid in the pipettes to 0.2 ml. Repeat the experiment and

record your data in table 6.4.

25 cm - Repeat the equilibration, adjustments and measurements at the 25 cm mark. Record

your data in Table 6.4.

Slide 10

Exercise #6 PHOTOSYNTHESIS

The changes observed in the tube containing Elodea are the

result of two simultaneous happenings:

1) the production of oxygen by Elodea which will always

result in an increase in volume, and

2) fluctuations in temperature and pressure, which is why

the pipette is set at the 0.2 ml mark.

To obtain a true reading of oxygen production, you must

subtract the control reading from the Elodea reading.

Slide 11

Exercise #6 PHOTOSYNTHESIS

Graphic Analysis

Plot all three cumulative movements of fluid as a function of time

on a sheet of graph paper.

It is suggested that different plotting symbols be used for each

distance from the light source (e.g. * for 75 cm; + for 50 cm; and

- for 25 cm).

Using a clear plastic ruler, draw a straight line that best fits all

points for each distance. Your lines should indicate that the greater

the light intensity, the greater the rate of oxygen production

by the plant.

Slide 12

Exercise #6 PHOTOSYNTHESIS

CONCLUSIONS

1) You have seen that plants contain photosynthetic pigments.

2) Such pigments (chlorophyll) absorb only specific

wavelengths of light.

3) The amount of light that the plant is exposed to has an

influence on photosynthetic rate.