All students who come to Oxford University are associated with an Oxford college. There are 21 Oxford colleges that offer Biology. Each college has its own particular history, ethos and architecture but the quality of teaching you receive is identical. Colleges normally provide students with affordable accommodation for at least two (the first and last) years of the course and act as a social hub. In Biology, all your lectures, practicals, field courses and indeed exams will be organised by, and based in, the Departments of Plant Sciences and Zoology.
How do I choose a college?
You can name a college at the application stage (your “first-choice” college), but this is not essential. Around 20% of students happily end up at a college different to the one they originally applied to. Also note, that some redistribution is necessary so some applicants may not be interviewed by the college they applied to.