Temperature vs rate graph

Shape: rate increases as temperature rises, reaches a peak (optimum temperature), then drops sharply.

Explanation: below the optimum, increasing temperature gives enzyme and substrate molecules more kinetic energy → more frequent successful collisions → faster rate. At the optimum, the rate is at its maximum. Above the optimum, the enzyme denatures: the active site changes shape permanently, so the substrate can no longer fit → rate drops to zero.

pH vs rate graph

Shape: bell curve with a peak at the optimum pH. Rate decreases on both sides of the optimum.

Explanation: each enzyme has an optimum pH where its active site is the correct shape. Moving too far from this pH (in either direction) changes the shape of the active site (denaturation) → substrate cannot bind → rate decreases.

Substrate concentration vs rate graph

Shape: rate increases steeply at first, then levels off to a plateau.

Explanation: initially, increasing substrate concentration means more substrate molecules are available to bind to enzyme active sites → rate increases. Eventually, all enzyme active sites are occupied (saturated), so adding more substrate does not increase the rate → plateau. The only way to increase the rate further is to add more enzyme.