Iodine Staining in Plant Cells Steps:

• Iodine solution tests for presence of starch in cells.
• Starch grains form a blue-black color with iodine due to chemical reaction.
• Cell walls consist of cellulose, which does not react with iodine.
• Cell walls retain the natural orange-brown hue of the iodine solution.

Why D is correct:

• Iodine reacts specifically with starch to produce blue-black color, while cellulose in cell walls remains orange-brown, as per the standard iodine-starch test.

Why the others are wrong:

• A: Cell walls do not stain blue-black; only starch does.
• B: Starch grains stain blue-black, not orange-brown; colors are reversed.
• C: Starch grains turn blue-black, not orange-brown.

Final answer: D