Final answer:
Enzymes lower the activation energy of chemical reactions, making them proceed faster than they would without the enzyme. They are essential for life because most cellular reactions would be too slow at body temperature to maintain living processes.
Step-by-step explanation:
Enzymes are crucial in catalyzing chemical reactions because they lower the activation energy required for a reaction to occur. While a chemical reaction can technically happen without an enzyme, the rate at which it would proceed is usually very slow due to the high activation energies involved. An enzyme provides a reaction pathway with a lower energy barrier, thereby significantly increasing the reaction rate under physiological conditions.
By binding to the reactant molecules and orienting them properly, enzymes increase the likelihood of reactants interacting in the correct way to proceed with the reaction. This unique ability means enzymes are essential for sustaining life, as most cellular reactions would be far too slow at normal body temperatures to be beneficial for the cell without their assistance. Without enzymes, the complex and finely tuned metabolism that characterizes living organisms would not be possible.
Therefore, the correct answer to the question is b) Enzymes lower the activation energy of the reaction. They do not change the direction of the reaction or increase the temperature of the reaction, nor are they non-essential; they are indispensable for facilitating the myriad of chemical reactions that occur within living organisms.