Temperature can affect rate of reaction. As temperature increases, rate of reaction also increases, because enzymes have more kinetic energy. This continues up to the optimum temperature (for enzymes in humans, about 37 degrees). After this temperature, rate decreases because enzymes denature. This changes the shape of the active site so the substrate doesn't fit. pH can also affect rate of reaction. As pH increases, rate also increases. This continues up to the optimum pH (different for different enzymes). After this pH, rate decreases because enzymes denature and the shape of the active site changes.Enzyme concentration can also affect rate of reaction. As enzyme concentration increases, rate of reaction increases because there are more enzymes available to react with substrates. However, after a point, rate of reaction plateaus. This is because all substrates are involved in reactions. Rate won't increase again unless substrate concentration is increased.