Final answer:
A prezygotic barrier is a mechanism that blocks reproduction from taking place by preventing fertilization. Gamete isolation and temporal isolation are two types of prezygotic barriers.
Step-by-step explanation:
A prezygotic barrier is a mechanism that blocks reproduction from taking place by preventing fertilization when organisms attempt reproduction. One type of prezygotic barrier is gamete isolation, which occurs when differences in the gamete cells (eggs and sperm) of organisms prevent fertilization. For example, closely related organisms may try to mate, but their reproductive structures simply do not fit together, preventing successful fertilization. Another type of prezygotic barrier is temporal isolation, where differences in breeding schedules of organisms prevent them from reproducing at the same time.