No, biology is not a compulsory subject for the National Defence Academy (NDA) exam. The NDA exam is a competitive examination in India conducted by the Union Public Service Commission (UPSC) for admission to the Indian Army, Navy and Air Force. The exam consists of two parts: a written test and an interview. The written test includes subjects such as mathematics, English and general knowledge. Candidates are not required to have studied biology to be eligible for the NDA exam.