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?
Leaves on the shady side (or plants kept in shade) have darker green leaves compared to those on the sunny side.
This happens because in shady conditions, light becomes a limiting factor for photosynthesis. The context states that "light saturation occurs at 10 per cent of the full sunlight" and "except for plants in shade or in dense forests, light is rarely a limiting factor in nature." This means plants in shade receive less than optimal light intensity.
To compensate for low light availability and maximize light absorption for photosynthesis, plants in shade produce more chlorophyll pigments. As the context explains, the green colour of leaves is due to chlorophyll pigments (Chlorophyll a - bright or blue green, and Chlorophyll b - yellow green). The higher concentration of chlorophyll in shade-grown leaves makes them appear darker green in colour.
Explanation
This question tests understanding of how light intensity affects chlorophyll content in leaves. The textbook context establishes that light is a limiting factor for plants in shade (Section 11.10.1) and that leaf colour is determined by chlorophyll pigments (Section 11.4). Students need to connect these concepts: when light is limited, plants produce more chlorophyll to maximize light capture, resulting in darker green leaves. This is a common adaptation where shade-grown leaves have higher chlorophyll density per unit area compared to sun-exposed leaves.
Solution Steps
Step 1: Identify which leaves are darker green - shady side leaves are darker green
Step 2: Explain why - in shade, light is a limiting factor for photosynthesis
Step 3: Connect to chlorophyll - plants produce more chlorophyll to capture maximum available light
Step 4: Conclude - higher chlorophyll concentration makes leaves appear darker green