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Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

The production of the chlorophyll pigment essential for photosynthesis is directly proportional to the amount of light available. In the absence of light, the production of chlorophyll-a molecules stops and degrades slowly. This changes the colour of the leaf gradually to light green. The xanthophyll and carotenoid pigments become predominant as they are not degraded, causing the leaf to become yellow. These pigments are more stable as light is not essential for their production.

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Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?

Give comparison between C₃ and C₄ pathways.

Suppose there were plants that had a high concentration of Chlorophyll-b, but lacked chlorophyll-a, would it carry out photosynthesis? Then why do plants have chlorophyll-b and other accessory pigments?

Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:

(a) At which point/s (A, B or C) in the curve is light a limiting factor?

(b) What could be the limiting factor/s in region A?

(c) What do C and D represent on the curve?

Photosynthesis in Higher Plants

Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?