Final answer:
Increasing the substrate concentration generally leads to an increase in enzyme activity under normal physiological conditions, until the enzyme becomes saturated and can bind no additional substrate. Temperature and pH also affect enzyme activity, with each enzyme having an optimal range for function. The correct option is B. Increases.
Step-by-step explanation:
Effect of Substrate Concentration on Enzyme Activity
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process. They are highly specific to their substrates and work best under optimal conditions of temperature and pH. One important aspect of enzyme function is how their activity changes with varying substrate concentrations.
Under normal physiological conditions, if the concentration of a substrate is increased, the activity of an enzyme that functions optimally under those conditions typically increases. This happens because there are more substrate molecules available for the enzyme to bind to, which accelerates the reaction rate. However, this relationship only holds until the point of saturation is reached. At saturation, all enzyme active sites are occupied, and adding more substrate does not further increase enzyme activity.
When considering environmental factors such as temperature and pH, enzymes have an optimal range in which they function most efficiently. Beyond these ranges, enzyme structure and therefore function can be compromised. For example, high temperatures may lead to denaturation, which is the breakdown of the three-dimensional structure of the enzyme, rendering it inactive. Moreover, pH levels that are too high or too low can disrupt the delicate balance of ionic and hydrogen bonds within the enzyme, again leading to a loss of structure and function. Therefore, within the context of physiological conditions, if we increase the substrate concentration, the enzyme activity increases until the active sites become saturated. After that point, the additional substrate will not further increase enzyme activity. The correct option in the final part, given the information provided, is 'B. Increases'.