Question

which substance turns a blue - black colour when treated with a few drops of iodine solution?
○ a. table sugar
○ b. powdered milk
○ c. table salt
○ d. white bread

a certain enzyme will hydrolyze egg white but not starch. which statement best explains this observation?
○ a. enzyme molecules are specific in their actions
○ b. starch molecules are too large to be hydrolyzed
○ c. starch is composed of amino acids
○ d. egg white acts as a coenzyme for the hydrolysis

Explanation:

• First question: Iodine solution reacts with starch to form a blue - black complex. White bread contains starch. Table sugar (sucrose), powdered milk (proteins, fats, etc.), and table salt (NaCl) do not react with iodine to give a blue - black colour.
• Second question: Enzymes are specific in their actions. They have an active site that is complementary to a specific substrate. The enzyme in question has an active site that fits the substrate in egg white (likely a protein) but not the starch molecule. Starch molecules are not too large in a general sense for hydrolysis (there are enzymes like amylase that can hydrolyze starch). Starch is composed of glucose units, not amino acids. Egg white is a protein (substrate here), not a coenzyme.

Answer:

• First question: d. White bread
• Second question: a. Enzyme molecules are specific in their actions