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Difficulty: EasyPlant Nutrition and Photosynthesis

Arrange the standard experimental steps for testing a green leaf for the presence of starch in the correct chronological sequence from start to finish.

  1. 1Boil the green leaf in water for a few minutes.
  2. 2Boil the leaf in ethanol using a water bath.
  3. 3Rinse the decolorized leaf in warm water.
  4. 4Spread the leaf on a white tile and add a few drops of iodine solution.

Answer

The correct sequence of steps to test a green leaf for starch is: (1) Boil the green leaf in water, (2) Boil the leaf in ethanol using a water bath, (3) Rinse the decolorized leaf in warm water, and (4) Spread the leaf on a white tile and add a few drops of iodine solution.
The correct experimental sequence ensures that plant cell membranes are permeable, green pigments that mask color changes are extracted safely in a water bath, the leaf is rehydrated to soften it, and iodine solution can react clearly with any stored starch.

Step-by-Step Solution

1
Boil the green leaf in water
Cell membranes become permeable and enzymatic activity ceases.
High temperature kills the cells and prevents further biochemical reactions.
2
Extract chlorophyll pigment using ethanol in a water bath
The leaf turns pale white/yellowish as chlorophyll dissolves in ethanol.
Decolorization is necessary because green chlorophyll masks the blue-black color of positive starch reaction.
3
Rinse the leaf in warm water
The leaf becomes soft and pliable.
Alcohol dehydration makes the leaf stiff and brittle; water restores flexibility.
4
Add iodine solution
A blue-black color develops if starch is present.
Iodine reacts specifically with starch molecules to form a characteristic blue-black complex.

Key Concept

Starch test procedure as evidence of photosynthesis in green plants
Estimated Time:45s
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Topics

Plant Nutrition and Photosynthesis

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