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In Went's classic experiment, why did the decapitated Avena coleoptile grow straight up after an agar block that had held the cut tip was placed on it?
AThe agar itself supplied nutrients for fresh cell growth
BLight striking the agar block triggered the growth
CThe plain agar block physically supported the stump
DA chemical from the tip had diffused into the agar block
Answer & Solution
Correct answer: D. A chemical from the tip had diffused into the agar block
1. A plain agar block placed on a decapitated coleoptile produced no growth response.
2. When a block that had first held the cut tip was used, the coleoptile grew straight up.
3. This showed a chemical had diffused from the tip into the agar and then stimulated growth.
4. Went named this chemical auxin, so plain agar nutrients or mere physical support do not explain it.
5. The experiment was done in darkness on detached tips, so light is not the cause.
6. Thus the diffusible chemical, later named auxin, is the cause of the renewed straight growth.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 16 Plant and Animal Hormones "Went's Experiment", p.237_
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