1) What does this diagram tell us?
This graph shows that the rate of reaction is affected by enzymes. If we add an enzyme to a reaction the rate of that reaction will increase.
2) Effect of enzyme on reaction.
The enzyme increases the rate of the reaction. This happens because gives an alternative way for the reaction to occur. Lower activation energy.
3) Why does the shape of the reaction with the enzyme flatten out?
This means that the enzyme reaches a speed limit and cannot go over it.