Q. Organisms use bio-catalyst to break down complex substances into simpler substances. These bio–catalysts are called ____:
Answer: Enzymes
Notes: Enzymes are sometimes called biological catalysts because they speed up reactions, and only small amounts are required. Digestive enzymes speed up the breakdown of complex food substances into simpler subunits. The breakdown of food in digestion is actually caused by water chemically splitting the complex food molecules, a process called hydrolysis.