The correct answer is B. The substrate will be broken down much more slowly.
Fever can cause a change in the shape of an enzyme's active site due to the increased body temperature, which can lead to denaturation of the enzyme. When the active site changes shape, the enzyme may not bind to its substrate effectively, resulting in a slower reaction rate for the breakdown of the substrate.
Let's briefly analyze the other options:
A. The enzyme will choose to bind to a different substrate. - Enzymes do not choose substrates; they have specific shapes and active sites that determine which substrates they can bind to. If the active site changes shape, it may no longer fit the original substrate but won't "choose" to bind to another.
C. The enzyme-substrate complex will be more stable. - If the enzyme's active site has changed shape due to temperature changes, the enzyme-substrate complex would likely be less stable, not more.
D. The resulting amino acids will be different shapes. - The amino acids themselves will not change shapes; however, the overall structure of the enzyme may be altered due to denaturation. This option doesn't accurately reflect the effect on the enzyme activity.
Thus, option B is the most appropriate choice based on the impact of increased temperatures on enzyme activity.