Your bacterium is growing on a type of medium called casein agar, which contains milk protein (casein). there is a clear zone around the growth area of the bacterium, showing that it is synthesizing the enzymes needed to catalyze the breakdown of casein. these enzymes are considered:

a. apoenzymes.
b. exoenzymes.
c. ribozymes.
d. regulated enzymes.
e. endoenzymes.

B. exoenzymes.

Explanation:

Exoenzymes are the extracellular enzymes that are secreted by certain microbes. For instance, gram-positive bacteria secrete certain exoenzymes to degrade polymeric nutrients that are otherwise be too large for transport across the cell membrane. In the given example, the bacterium is grown on casein agar and the bacterium is secreting casein digesting enzymes in the medium to degrade casein. Since the enzymes are extracellular enzymes, they represent exoenzymes.