Human Health GCSE

Do you mean additional Science ?

If you mean you have core and additional science, then I'm sure it will be fine, most specify grades for double science and grades for triple science that they will accept. The only issue would be if for A level you need triple to do science A levels, but that depends on your college/sixth form, as obviously for vet med you need some science A levels

Science though? As the above poster said provided that they allow you to do Additional Science most colleges will allow you to do the A Level based on that. I only did additional science and I did A Level Biology

No not at all, when I started A Level Biology at least I found that everyone had different gaps in their knowledge because of the different exam boards anyway, whereas some were taught one thing at additional science other people were not or at least not in the same amount of detail. Everyone is in the same boat and I didn't find that not having triple or extended science disadvantaged me in anyway at all. You should be fine.

Besides the first topic of A Level Biology or at least on WJEC exam board was designed to teach everyone the skeleton that was A Level Science so we learnt about things like what makes up DNA, the structures inside our cells, cell division, water potential; parts of Biology which would later come into use in other topics so after teaching this topic or module everyone was on the same level and the same page. You should be fine but I really cannot stress this enough to you, revise from day one because A Levels are such a big jump from GCSE's that you cannot start revising a few days or even a few weeks before your exam at least, most people can't. Just keep working throughout the year and you should be fine