Which statement about zero-order kinetics is true?

Which statement about zero-order kinetics is true?

• A. The rate is independent of substrate concentration
• B. The rate is proportional to substrate concentration
• C. The rate is inversely proportional to enzyme activity
• D. The rate is determined by product concentration

Answer: (A)

Zero-order kinetics means the reaction rate stays constant and does not change with different substrate levels. This happens when the catalyst (often an enzyme) is saturated with substrate, so every catalytic site is busy and adding more substrate can’t speed things up. The rate then is set by how fast the enzyme can turnover substrate, essentially the maximum rate given the amount of enzyme present. That’s why the true statement is that the rate is independent of substrate concentration. If the rate were proportional to substrate concentration, that would be first-order behavior, not zero-order. If the rate were inversely related to enzyme activity, increasing enzyme activity would slow the reaction, which isn’t how kinetics work. If the rate were determined by product concentration, the rate would depend on how much product has formed, which isn’t the defining feature of zero-order kinetics either.

Zero-order kinetics means the reaction rate stays constant and does not change with different substrate levels. This happens when the catalyst (often an enzyme) is saturated with substrate, so every catalytic site is busy and adding more substrate can’t speed things up. The rate then is set by how fast the enzyme can turnover substrate, essentially the maximum rate given the amount of enzyme present.

That’s why the true statement is that the rate is independent of substrate concentration. If the rate were proportional to substrate concentration, that would be first-order behavior, not zero-order. If the rate were inversely related to enzyme activity, increasing enzyme activity would slow the reaction, which isn’t how kinetics work. If the rate were determined by product concentration, the rate would depend on how much product has formed, which isn’t the defining feature of zero-order kinetics either.