There are several routes through science at KS4:

Triple Science (OCR 21st Century Science): 

A two year course in three separate GCSEs (Biology, Chemistry and Physics)

Each GCSE comprises seven modules and coursework.  Exams in June Y10, January and June in Y11.

Core Science: This gives a single GCSE.  There are two courses: 21st Century OCR and AQA .

Additional Science: This builds on the Core, gives a second GCSE, and is suitable for pupils thinking of studying science at A level.

Applied Science: Also builds on Core, gives a separate "Applied Science" GCSE which applies science to everyday life and work.  It is suitable for all pupils, but is not an A-level science qualification.

Two common routes are "Core + Additional" and "Core + Applied".

Try this site:  http://www.revisionworld.co.uk/gcse