Does the word biology have to be capitalized in a sentence?

No, the word "biology" does not need to be capitalized in a sentence unless it is the first word of a sentence or part of a proper noun.

Here are some examples:

* Correct: I am interested in biology.

* Correct: Biology is the study of living organisms.

* Correct: I took a course in Marine Biology at the university.

Let me know if you have any other questions!