Interpreting Biological Molecule Test Results

Steps:

• Identify tests: Iodine turns blue-black for starch; Benedict's gives red precipitate for reducing sugars; Biuret turns violet for proteins.
• Examine sample results: Positive iodine (starch present); negative Benedict's (no reducing sugar); negative Biuret (no protein).
• Match to conclusions: Only starch indicators align with option A.
• Confirm no other positives: Rules out sugars or proteins.

Why A is correct:

• Iodine test positive indicates starch; negatives for others confirm starch only, per standard biochemical test definitions.

Why the others are wrong:

• B: No Benedict's or Biuret positives, so no reducing sugar or protein.
• C: Iodine positive shows starch present, not just reducing sugar.
• D: Biuret negative excludes protein, despite starch.

Final answer: A