Zoologists are the ones who find out that snakes are poisonous, that birds are really reptiles, that fish evolved in fresh water, and that most of the described organisms on earth are beetles. Things are going extinct every day, without any mourning on the part of the human populace because they simply don't know they exist. So many different kinds of plants and animals have been used in breakthrough drug treatments - the endangered Yew tree, in California, for example, is the source for taxol, a chemical compound that shows some promise in treatment of cancer. African clawed toads have miraculous regenerative properties in their skin. You have to know what's closely related before you use them.
Zoologists can predict what's closely related using their techniques of observation and analysis.
Some people with bachelor's degrees in zoology go on to become veterinarians. I work on insects now, and get at least three or four calls a month from people who have called the university asking about a particular bug that just bit them, ate most of their garden, or pupated in one of their house plants. I hope this has been useful to you. Copyright 1996, Washington University. All rights reserved.