Getting a 6 is not difficult at all and you should easily get a 6 in your GCSE if you don't make a significant number of mistakes. Although examiners want to assess a basic level of competence on the GCSE exam, they still want to distinguish between candidates who can apply their previous knowledge in unknown contexts and those who cannot. The equivalent GCSE grades Grade 5 is a “strong pass” and equates to a high C and a low B in the previous grade system. Show colleges and universities that you've only done the bare minimum to pass your GCSE subjects.
Science subjects such as Biology, Chemistry, and Physics (along with any combined version) are also some of the easiest subjects to pass at GCSE. Although a 6 is a good GCSE grade, it will prevent you from participating in many competitive colleges and university programs. Even if you study half-heartedly throughout the year and increase your level as you approach your exams, getting a 6 in your GCSE shouldn't be too difficult. Search results for My daughter sat at her GCSE job in June and 4 of the questions weren't even in the curriculum.
This would be common with most year 7 students, since a grade 3 in year 7 is not fully equivalent to a gcse grade.