Which one of the following statements is true of enzyme catalysts? A) Their catalytic activity is independent of pH. B) They are generally equally active on D and L isomers of a given substrate. C) They can increase the equilibrium constant for a given reaction by a thousand-fold or more. D) They can increase the reaction rate for a given reaction by a thousand-fold or more. E) To be effective, they must be present at the same concentration as their substrate

D) They can increase the reaction rate for a given reaction by a thousand-fold or more.

Explanation:

Enzymes are like catalysts with the only difference that they are bio-molecules. Biochemical/chemical reactions are slow because of 'transition state barriers' which require a lot of energy to overcome so enzymes rather than overcoming transition state barrier provide an alternate pathway for biochemical reactions which require comparatively less energy. Thus presence of an enzyme leads to an increase in reaction rate because alternate pathway which requires less energy makes the rate of chemical reaction rapid by a thousand-fold or more.

b. the carbon cycle ensures living things have a source of hydrogen