Question

1. What Region of visible light spectrum yields the highest photosynthetic rates in spinach? What regions yield the lowest photosynthetic rates? How do you know? (See graph below)

2. 2. Green photosynthetic pigments (e.g., chlorophyll a and b) capture energy from a wide—but not the widest possible—region of the visible spectrum of light. What pigment color would enable plants to capture energy from almost the entire spectrum of visible light? Why, then, are most plants green? (see graph below)

3. 6. Describe the impact of green light, blue light, and DCMU on photosynthesis. Use data to support your answer.

Time (min)	Tube 1-Control Dark	Tube 2-DPIP & Dark	Tube 3- DPIP & White Light	Tube 4-DPIP & Green Light	Tube 5-DPIP & Blue Light	Tube 6-DPIP & DCMU
1	0	0.419	0.355	0.358	0.423	0.449
5	0	0.427	0.171	0.284	0.375	0.446
9	0	0.416	0.015	0.224	0.321	0.44
13	0	0.417	0.017	0.133	0.251	0.448
17	0	0.43	0.005	0.105	0.231	0.447

Answer 1

1. Light in range between blue and red yields the highest photosynthetic rates. Red light yields maximum as photosystems 1 and 2 operates at 700nm and 680nm, which falls in red range.

Green light yields the lowest photosynthesis, because green light is reflected not absorbed.

2.2.

Black pigment could absorb energy from entire spectrum.

Most plants are green, because they contain chlorophyll necessary for photosynthesis. Cholorophyll absorbs blue and red light but reflects green light hence appear green.

3.6.

Effect of green light on photosynthesis.

In green light photosynthesis is minimum.

Green light alters plant architecture by increasing shoot length, so that other colours are absorbed.

Effect of blue light on photosynthesis.

In blue light photosynthesis rate is good. however it suppresses shoots growth and plants are shorter and have smaller, thicker and darker green leaves.

Effect of DCMU on photosynthesis.

DCMU is a inhibitor of photosynthesis. It blocks the plastoquinone binding site of photosystem II in electron transport chain. Hence it is used as a herbicide.