Develop only a single topic in each paragraph. Arrange paragraphs in sensible order. Shortcomings in these areas will lower the grade. At least for the first one or two assignments of each type, the instructor will return unsatisfactory work, with suggestions, and the student will revise and resubmit the work until it is satisfactory. Writing is more than a means of displaying what you know.
Writing is a means of learning.
The resulting increase in your knowledge and understanding is a product of writing about the subject. Writing is part and parcel of the learning that begins, but is not completed, in the lab. Writing is a means of eliminating distractions. It forces you to push away the irrelevant and to gather the relevant, and then to concentrate on the subject until you understand it in detail. Even the best writers cannot produce a final draft on the first try.