A variegated plant has green and white (non-green) regions on the same leaf. When such a leaf is tested for starch after being kept in sunlight, only the green regions turn blue-black with iodine while the white regions remain colourless. What does this result tell us about the role of chlorophyll in photosynthesis?
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
The result proves that chlorophyll is essential for photosynthesis.
- The green regions of the leaf contain chlorophyll (in chloroplasts), so they could carry out photosynthesis in sunlight and produce starch. Iodine turned these regions blue-black, confirming starch is present.
- The white (non-green) regions lack chlorophyll, so no photosynthesis occurred and no starch was produced. Hence, iodine showed no colour change in these regions.
This demonstrates that even when sunlight and CO₂ are available, photosynthesis cannot take place without chlorophyll. Chlorophyll absorbs light energy, which is the first essential step of photosynthesis.
Source: Life Processes, Section 5.2.1 (Activity 5.1)
---
Explanation
The examiner expects three clear points for 3 marks:
- Green regions have chlorophyll → photosynthesis occurs → starch present → blue-black with iodine.
- White regions lack chlorophyll → no photosynthesis → no starch → no colour change.
- Conclusion: chlorophyll is essential/necessary for photosynthesis.
Avoid vague statements like "chlorophyll helps in photosynthesis" — say it is essential. The activity is directly from the textbook (Activity 5.1), so examiners expect you to reference what the colour change of iodine indicates.