The Research Based Curriculum packs (RBCs) are short activity and reading packs made from real-world research by an actual PhD student at a British university. They are designed for students like you, who are trying to gain experience in their subject, show they are committed to applying to university and want to stretch their intellectual skills.
By completing one or more of these packs, you are able to demonstrate on your UCAS Personal Statement an in-depth understanding of your subject. It also shows you have made a real effort to consider your options and improve your knowledge which is attractive to universities, even if the subject isn't exactly what you will study (like a pack on microbiology when you are interested in environmental studies)
Packs are written for both Key Stage 4 and 5, but this is something you should explore and complete by the end of Year 12 ideally. You could do one in Year 13 as long as it's a few months before you apply to university.
Not sure which one to select? Ask a teacher you trust!