Just describing how each factor actually affects enzyme activity:
*Heat - By adding heat, you overcome/break the weak intermolecular bonds (such as hydrophobic interactions and hydrogen bonding) that hold the shape of the secondary and tertiary structures in the enzyme, and hence the enzyme will denature and enzyme activity will sharply drop after the critical point (the temperature where enzymes begin to denature)
*pH - In order to maintain a constant level of pH, amino acids in the enzyme will donate or accept hydrogen ions, so that the pH level is stabilised. However, this changes the intermolecular bonds that form between the secondary and tertiary structures (as you've pretty much changed the chemical structure of the amino acid), and hence the protein will denature. The curve for pH affecting enzyme activity resembles a bell-curve because the pH scale is a logarithmic scale, which means that it goes up in factors of 10 (pH 6 is 10 times more acidic, and has 10x more hydrogen ions than pH 7), and so the drop in enzyme activity is not as dramatic as temperature.
*Co-enzymes - these basically help the enzyme to accommodate the substrate better, and make it easier to fit. Hence, enzyme activity will increase as more substrates will easily bind to the active site of the enzyme.
*Inhibitors - These are divided into two categories, non-competitive and competitive, which bind completely to an enzyme's active site, preventing the substrate from binding to the enzyme. If you have a high concentration of competitive inhibitors, enzyme activity will decrease as less substrate is able to bind to the active sites of enzymes. However, if the concentration of substrate is greater than the concentration of competitive inhibitors, enzyme activity will decrease less as the substrate becomes more 'competitive', and there is a lesser likelihood of an inhibitor binding to an active site. Non-competitive inhibitors almost permanently bind to enzymes, halting reactions between substrates and enzymes completely.
-Concentration of enzyme - Obviously, as you increase the concentrations of enzyme, there will be a great increase in the rate of reaction - more enzymes are bumping and binding into substrates.
-Concentration of substrate - Initially, increasing the substrate concentration will increase the rate of reaction as there is a greater chance of substrates binding to active sites, but it slowly decreases as the enzyme concentration becomes 'saturated', which is when the enzymes are reacting at full capacity and cannot increase the rate of reaction.
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