Lab Photosynthesis

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should you do to change its concentration.

Once you have reached an appropriate %T reading you are ready to

continue with the experiment.

Slide 5

Exercise #6 PHOTOSYNTHESIS

Use your chlorophyll extract along with an ethanol blank and

determine the absorbance of the chlorophyll solution at various

wavelengths.

NOTE: the procedure employed here is identical to that used in the determination of the

absorption spectrum for methylene blue (Exercise #3)

-remember to zero the machine after you change each wavelength.

In order to clearly visualize the actual absorbance characteristics

of your chlorophyll extract, you will plot your data using graphic

analysis.

Remember that wavelength is the independent variable and

that absorbance is the dependent variable. Indicate with

arrows on the x-axis the wavelengths of light most strongly

absorbed by the chlorophyll extract.

Slide 6

Exercise #6 PHOTOSYNTHESIS

Light Intensity And Photosynthesis

In general, as the intensity of light increases, the rate of

photosynthesis increases.

How does one measure the rate of photosynthesis?

As you should recall, oxygen is a by-product of photosynthesis.

Therefore, the photosynthetic rate can be determined by

measuring the rate of oxygen production by the plant.

During this portion of the laboratory you will observe the effect

of light intensity on oxygen production and then make a generalization

on plant survival based upon the data you have collected.

Slide 7

Exercise #6 PHOTOSYNTHESIS

PROCEDURE

To determine the effect of light intensity upon photosynthetic rate,

you will conduct the following experiment:

1) Obtain a piece of Elodea 5 to 6 inches in length and place it in a test tube with the cut end up.

2) Fill the test tube with NaHCO3 (serves as a source of CO2) and plug with the rubber stopper containing

the bent glass pipette an a syringe.---AVOID AIR BUBBLES!

3) The position of the fluid in the pipette can be adjusted by raising or lowering the plunger in the syringe

4) Prepare a second tube filled with NaHCO3 without Elodea to act as a control for temperature and

pressure fluctuations.

5) Place both tubes in a beaker filled with room temperature water.

6) Place a lamp 75 cm from the experimental beaker and set up a heat filter (additional beaker) filled

with tap water placed half way between the light source and the experimental beaker.

Refer to the picture on the following slide for reference.

Slide 8

Exercise #6 PHOTOSYNTHESIS