There are no examinations in lab but you are expected to learn skills that are tested by doing projects such as your unknowns. Some students have a lot of laboratory experience and others do not. Some are better at the microscope than others. If you have more experience, help out those who don't. And if you have difficulty be persistent.
Success often comes after trying over and over.
The microbes do seem to get larger as the semester goes on. Hand in all assignments. Grades of zero on assignments that aren't handed in, really hurt your average.