If a leaf is first kept in darkness and then placed in light without carbon dioxide, what is expected in the starch test?
Answer and explanation
Correct answer: Very little starch or no starch will form
The dark period is used to destarch the leaf: stored starch is consumed in respiration. During the subsequent light period, photosynthesis still requires carbon dioxide as a raw material. Since carbon dioxide is absent, little or no new carbohydrate is produced, so iodine will not show the usual blue-black starch colour, or it will show it only weakly. Therefore option B is correct; the other statements contradict photosynthesis and plant physiology.
Frequently asked questions
What is the correct answer to this question?
Very little starch or no starch will form
Why is this the correct answer?
The dark period is used to destarch the leaf: stored starch is consumed in respiration. During the subsequent light period, photosynthesis still requires carbon dioxide as a raw material. Since carbon dioxide is absent, little or no new carbohydrate is produced, so iodine will not show the usual blue-black starch colour, or it will show it only weakly. Therefore option B is correct; the other statements contradict photosynthesis and plant physiology.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: World of Living. Topic: Life Processes.
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