Yes and yes. On the UCAS form, you have to list when you took the examination. The sciences can be re-taken. The coursework marks for the Individual Skills Assessment can be carried forward from the previous sitting or re-taken if appropriate supervision can be found (such as at a local school, college or adult education class). It depends on his grades. It is worth looking at the entry requirements for the universities in which he is interested. The literature will only provide a general guide, but it is a useful indication nevertheless. Good luck