How might altering the substrate concentration affect the rate of the reaction? Why?

You've already answered it. By increasing the amount of substrate you have increased the concentration provided you've kept a constant volume.

enzymes have optimum working temperatures and ph's. If an enzyme is in its optimum ph selection, then changing the ph will decrease the reaction fee of that enzyme. for occasion, enzymes in the lysosome desire a low pH to function. for this reason contained in the lysosome, the pH is low. If enzymes from contained in the lysosome go out the lysosome and enter the cytoplasm, the enyzmes won't perform.