Final answer:
b) Substrate is the rate-limiting factor.The rate of an enzyme-catalyzed reaction increases with substrate concentration only if substrate is the rate-limiting factor.
Step-by-step explanation:
Increasing the concentration of substrate will increase the rate of reaction only if substrate is the rate-limiting factor. When the enzyme concentration is kept constant, increasing the substrate concentration leads to a higher reaction rate up until the point where enzymes become saturated with the substrate.
At saturation, all active sites of the enzymes are occupied, and additional substrate molecules can no longer increase the reaction rate because there are no available enzyme molecules to bind with.
This is demonstrated in a hyperbolic curve when plotting velocity against substrate concentration. The reaction rate will continue to increase with higher substrate concentrations until saturation, beyond which the rate remains constant.
An increase in enzyme concentration would also increase the rate of reaction, provided there is an excess amount of substrate. This relationship is linear and demonstrates that the reaction rate is directly dependent on the enzyme concentration under these conditions.
Both enzyme and substrate concentrations are crucial in determining the reaction rate, along with other factors such as temperature, pH, concentration of products, and presence of ions.