It may be confusing, even annoying, but some of the structures you may have learned in test prep classes and English language classes, such as the five-paragraph essay, may not be appropriate for use in other classes. Be careful to follow assignment instructions.
Reflection writing assignments are common in many classes, especially as a response to reading assignments. It is distinctive from other types of academic writing because it encourages the writer to write in the first person, but usually it has the same expectations as other academic writing assignments in other ways.
Longer is not always better! Limit your sentences to a few clauses, and alternate long sentences and short sentences. Academic writing in English tends to have long, sophisticated noun phrases, but it is not a requirement to include complex sentence structure and long strings of joined clauses.