Which of the following is NOT a characteristic of digestive enzymes?

Analyze the question: We need the statement that is false about digestive enzymes (the "NOT" option).

Concept: Enzymes are biological catalysts with these key properties:

• They are proteins in nature.
• They are sensitive to pH. Each enzyme has an optimum pH (e.g., pepsin works best in acid, trypsin in alkaline conditions).
• They are sensitive to temperature. Each has an optimum temperature (about 37°C for human enzymes). Very high temperatures denature them.
• They are affected by poisons/inhibitors (e.g., cyanide, heavy metals).
• Many enzyme reactions are reversible, since enzymes speed up reactions in both directions.

Checking each option:

• A. Changes in pH affect enzymes: True. Extreme pH changes alter enzyme shape and activity.
• B. Enzymes react best at high temperature: False. They work best at an optimum (moderate) temperature, and high temperatures denature them.
• C. Enzymes react reversibly: True. Enzymes can catalyse reactions in both directions.
• D. Affected by intake of poisons: True. Poisons and inhibitors reduce or stop enzyme activity.
• E. Protein in nature: True.

Answer: B is the statement that is NOT a characteristic of digestive enzymes.

Exam tip: Whenever you see "enzymes work best at high temperature," be suspicious. The correct phrase is "optimum temperature." Remember: Enzymes like it warm, not hot!