Which description best fits the graph of reaction rate against increasing substrate concentration at a fixed enzyme concentration?

  • A. A straight line rising forever
  • B. A curve that rises and then levels off as active sites fill
  • C. A curve that falls from the start
  • D. A horizontal line from the beginning

Explanation

At low substrate, rate climbs steeply with each added molecule, but once every active site are occupied the enzyme is saturated and the curve plateaus. A straight line would imply no saturation, which contradicts the finite number of active sites.

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