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Lab Photosynthesis




Slide 1

Exercise #6

Exercise #6


In the process of photosynthesis, several energy transformations

take place.

-Light energy is captured by plant cells and is converted into

electrical energy in the form of high energy electrons.

-The kinetic energy of the electron is transformed into

chemical energy in the bonds of ATP.

-The ATP, in turn, transfers the energy to the chemical bonds

of a glucose molecule.

Through this process, light energy from the sun is captured and

stored in the chemical bonds of sugar molecules.

Slide 2



Photosynthetic Pigments

The initial step of photosynthesis involves the capture of light

energy by the photosynthetic pigment, chlorophyll.

However, the plant does not absorb all of the light energy in

the visible portion of the electromagnetic spectrum.

-Figure 6.1 of your lab manual represents the visible

portion of the electromagnetic spectrum.

In this exercise, you will use the spectrophotometer to determine

which wavelengths of light are absorbed and which ones are

reflected by the chlorophyll molecule.

Slide 3

Exercise #6

Exercise #6

Photosynthesis Procedure

In order to study the absorbance of various wavelengths of light

by chlorophyll, you must first separate the pigment from the leaf tissue.

This is accomplished by following the procedure below:

1) Place a large spinach leaf into a 50 ml beaker and add 30 ml of ethanol.

2) Place the beaker with ethanol on a hot plate and slowly heat the solution taking care not to crush the

leaf or boil the ethanol solution.

3) As the chlorophyll exits the leaf tissue it will enter the ethanol solution and turn the color green.

4) Fill the cuvette approximately 2/3 full will the chlorophyll extract.

Refer to the diagrams on the

right for a representation of the

chlorophyll extract.

Slide 4



At this point, we wish to determine which wavelengths of light

are absorbed by the chlorophyll extract. However, we must first

ensure that the concentration of chlorophyll in the solution is

appropriate for the experiment.

To do this, follow the procedure below:

1) Set the spectrophotometer at 550 nm and depress the %T button.

2) Place a cuvette filled 2/3 full of ethanol into the sample compartment and calibrate to 100 %T.

3) In order to continue on with the absorption experiment you must obtain a reading between 65% - 85%.

-If you have a reading below 65%, your experimental solution is too concentrated--what

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