Question

vided in the notes? Experiment 8.3: Light and Photophosphorylation Now that you have determined which wavelengths of light are absorbed by the different plant pigments, it is time to determine which wavelengths of light are most effective in stimulating photophosphorylation. Students are provided with different colored cellophane (thin, transparent sheets made from regenerated cellulose) filters. These filters contain pigments that absorb some wave- lengths of light and transmit others. The wavelengths transmitted are those associated with the color seen. The filters restrict the wavelengths of light available to the plant for photosynthesis. Materials • Spinach leaves, fresh Beaker (100-ml Syringe (10-cc) * • Colored filters Hole punch NaHCO, (0.2%) * Lamp Black paper cylinder • Procedures 1. Obtain a spinach leaf, and using a hole punch, punch 10 leaf disks. 2. Remove the plunger from the syringe, insert the leaf disks, and replace the plunger. 3. Depress the plunger fully, without crushing, or damaging, the leaf disks, and Jaspirate 3 mL of bicarbonate solution into the syringe.

Answer 1

Q. Which of the following are controlled variables for exercise 8.3 ?

A. Distance from the leaf disk to the light source (light intensity).

B. Wattage of light source (light intensity).

C. Depth of bicarbonate solution.

D. Size of leaf disks.

Answer.

All the above parameters are constant throughout the exercise and hence all are controlled variables.

(A) is a controlled variable because the distance of all leaf disks, lying at the bottom of the beaker, is constant from the light source.

(B) The light source (lamp) intensity does not change throughout the experiment.

(C) Depth of bicarbonate solution is kept constant at 5 cm.

(D) Size of leaf disks is uniform since they have been cut using the same hole punch machine.