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NCERT Solutions Curiosity Chapter 10 .2.1 Leaves: the 'food factories' of plants — Activity 10.3: Let us check

Book page 141 to 14310 Updated on2026-09-05

Q1.
Non-green patches of the leaf obtained from the plant placed in sunlight do not turn blue-black. Does it indicate that there is no chlorophyll present in those patches?
Answer

Not necessarily. The correct conclusion is more careful: the non-green patches may not have sufficient chlorophyll to prepare enough starch for the iodine test to detect.

This is what Bhaskar recorded:

Table 10.2: Presence of starch in green and non-green parts of the leaves of plants
S.No.Light conditions for potted plantInitial colours before iodine testFinal colours after iodine test
1.Plant kept in sunlightGreen and non-green patches on the leafGreen patches of leaf turned blue-black (non-green patches unchanged)
2.Plant kept in the darkGreen and non-green patches on the leafNo change in colour
Why we must be careful: the iodine test detects starch, not chlorophyll. "No blue-black" only tells us that too little starch was made there to be detected. A small amount of chlorophyll may still be present in those patches — some coloured leaves even contain other pigments that hide the green.
Did you know? Some leaves look red, violet or brown because they contain more of these coloured pigments than green chlorophyll, which hides the green. Some of those pigments also help in photosynthesis — an iodine test on such a leaf can still turn blue-black.
Q2.
What do we infer from the observations listed in Table 10.2?
Answer

Two clear inferences:

  1. Chlorophyll is essential for making starch. In the leaf from the sunlit plant, only the green patches turned blue-black. Starch was produced exactly where chlorophyll was present.
  2. Sunlight is essential for making starch. The leaf from the plant kept in the dark for 36 hours showed no blue-black colour even on its green patches — chlorophyll alone, without light, made no starch.

Putting them together: chlorophyll helps in preparing starch in the presence of sunlight. Since starch is made in the leaves, leaves are called the 'food factories' of plants.

Part of leaf testedChlorophyllSunlightResult of iodine test
Green patch, plant in sunlightYesYesBlue-black — starch present
Non-green patch, plant in sunlightInsufficientYesNo colour change — starch not detected
Green patch, plant in the darkYesNoNo colour change — no starch
Non-green patch, plant in the darkInsufficientNoNo colour change — no starch
Tip: the tracing-paper sketch Bhaskar made before the test is the key to this activity. Without a record of where the green patches were, you could not match the blue-black areas to them afterwards.
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