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Dr. Ellen Turner, Instructor
POB Photosynthesis Lab
The purpose of experiment one is to demonstrate the reactants and products of photosynthesis. The purpose of experiment two is to demonstrate that energy is stored in plants in the form of starch. Experiment three demonstrates which colors of light are absorbed by plant pigments. Experiment four clearly demonstrates visually the different primary pigments and accessory pigments stored in the chloroplasts of spinach.
These are the materials needed for experiment one.
On the left is the bromothymol blue solution (basic) and on the right is the elodea leaves.
Addition of CO2 to Bromothymol solution makes the solution acidic. A pH indicator in the solution causes the color to change from blue green to yellow.
The bromothymol blue solution in the presence of carbon dioxide becomes acidic. The indicator in the solution turns yellow to indicate a low pH.
Place the acidic bromothymol solution and the elodea in a sealed container. It should look similar to the above.
Place the sealed containers in a source of heat and light. For the purposes of this experiment, an overhead projector can be used. The class set up one control group and four experimental groups.
The results here clearly show that the acidic bromothymol solution turns back to a basic solution. Here we see the target experimental group next to the control group.
Plant one versus plant two. Differences in appearance are apparent.
Boiling the two leaves to remove waxy coating from the exterior.
Boiling the leaves again in alcohol to remove the chlorophyll.
The leaves, after boiling. Remove the leaves and dye them with iodine. Shine a light on the remaining solution.
The leaves after iodine staining. On the left, the malnourished leaf contains very little starch. On the right, the nourished leaf has abundant starch.
The alcohol containing the pigments from the leaves fluoresces red when a light is shone on it.
The pigments emit a red light when light is shone on them and no electron acceptor is present.
On the left, ethyl alcohol. On the right, spinach placed in a mortar.
Use the mortar and pestle to grind the alcohol soluble pigments put of the spinach leaves.
Decanting the primary and secondary pigments using alcohol in combination with a mortar and pestle.
Place two test tubes, one with the chlorophyll containing solution and the other with a ballast solution of water or alcohol on opposing sides of the centrifuge to properly balance it.
A centrifuge uses gravitational and inertial forces to separate components of a solution by weight. The pigments settle to the bottom while anything else rises to the top.
Using curettes and alcohol, zero the spectrophotometer. Then, place the pigment solution in the machine to obtain a reading. Record the data as instructed, and be sure to zero the machine between each reading.
Using the pigment solution from experiment 3, use a capillary tube or pipette to place a line on chromatography paper shaped as shown on the right.
Place the paper so that it is able to soak in petroleum ether. Be very careful, as petroleum ether is quite flammable.
Placing the chromatography paper inside the bottle of ether. Place just the tip inside the ether and allow the rest to sit above. Please note: put the cap back on the bottle of ether after the paper is in place or the ether will evaporate.
The results of the experiment. Several lines each indicative of a separate pigment can clearly be seen.