No - you really must have that A in BIology. Most applicants will have some A*s - makes no difference. If you finish up with a B, there are a few places that will accept resits, although most require extenuating circumstances - you do not want to have to rely on that, and the options are very limited. I cannot emphasise enough - put everying into getting that A now, even if it means missing the A* in your other subjects