A plant is kept in darkness for 48 hours and then a leaf is tested for starch using iodine solution. What result would be expected and why?

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Question

A plant is kept in darkness for 48 hours and then a leaf is tested for starch using iodine solution. What result would be expected and why?

Accepted Answer

Orange-brown colour, because all starch was converted to sucrose for transport — Without light, photosynthesis cannot occur, so no new starch is produced. Existing starch is converted to sucrose and respired or transported away, leaving no starch in the leaf; iodine solution therefore remains orange-brown. Option A is incorrect because darkness prevents photosynthesis and thus starch production. Option C is a misconception — iodine only turns blue-black in the presence of starch, not in all plant tissue. Option D is scientifically inaccurate; chlorophyll does not interact with iodine in this way.

Answer

Orange-brown colour, because chlorophyll absorbed the iodine in darkness

Answer

Blue-black colour, because iodine always turns blue-black in plant tissue

Answer

Orange-brown colour, because all starch was converted to sucrose for transport

Answer

Blue-black colour, because starch was made during the dark period

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