Question

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

Answer 1

• Since leaves require light to perform photosynthesis, the colour of a leaf kept in the dark changes from a darker to a lighter shade of green.
• Sometimes, it also turns yellow. 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 they get broken slowly.
• This changes the colour of the leaf gradually to light green. During this process, the xanthophyll and carotenoid pigments become predominant, causing the leaf to become yellow.
• These pigments are more stable as light is not essential for their production. They are always present in plants.

Answer 2

• Photosynthetic cells all include carotenoid pigments.
• These are auxiliary pigments that are also present in petals, roots, etc.
• Because these pigments are difficult to break down, they unmask after the breakdown of chlorophyll, revealing their colour for a short while.
• As a result, a leaf stored in darkness will be either pale green or yellow.