The effect of substrate concentration on enzyme activity can be described using the Michaelis-Menten kinetics. As the substrate concentration increases, the reaction rate enzyme activity also increases, up to a certain point. This is because, as more substrate molecules are available, the enzyme has more opportunities to bind and convert the substrate into the product. However, once all the enzyme molecules are saturated with substrate, the reaction rate reaches its maximum Vmax and will not increase further, even if the substrate concentration continues to increase.In the presence of a competitive inhibitor, the relationship between substrate concentration and enzyme activity is affected. A competitive inhibitor is a molecule that resembles the substrate and competes with it for binding to the enzyme's active site. When a competitive inhibitor is present, it reduces the number of available active sites for the substrate to bind, effectively decreasing the enzyme's affinity for the substrate.This effect can be observed in the Michaelis-Menten equation:v = Vmax * [S] / Km + [S] where v is the reaction rate, Vmax is the maximum reaction rate, [S] is the substrate concentration, and Km is the Michaelis constant, which represents the substrate concentration at which the reaction rate is half of Vmax.In the presence of a competitive inhibitor, the apparent Km value increases, meaning that a higher substrate concentration is required to achieve the same reaction rate as in the absence of the inhibitor. However, the Vmax remains unchanged, as the enzyme can still reach its maximum reaction rate if the substrate concentration is high enough to outcompete the inhibitor.In summary, the substrate concentration affects enzyme activity by increasing the reaction rate until the maximum rate is reached. The addition of a competitive inhibitor affects this relationship by increasing the apparent Km value, requiring a higher substrate concentration to achieve the same reaction rate, but the Vmax remains unchanged.