It depends what you want to study. But generally, to study science at university, you need to have passed all your science and maths GCSE’s with a C or above. You will also have to take at least 3 A levels and 1 AS level in a relevant subject. Typically you will want to study maths and at least one other science at A level, but this is not always the case. The grades you need in your A levels to study science at university depends on what university you have applied to, but you will be able to check these out on line and by ringing admissions departments nearer the time. Like chris said too, go and have a chat with your career adviser, or visit your local connexions centre http://www.connexions-direct.com/index.cfm
Question: how many GCSE's and A levels doo you need to get to become a scientist?
Well – that depends on many things – you should talk to your teachers about the deatils. But you should be aiming for at least 3 good A level grades to get a university place. That is the first thing to do.
After that, if you enjoy your subjects (whatever they are) you should find it easier because you will be studying almost nothing but your favourites.