Essentials OCR Twenty First Century GCSE Biology offers clear and concise coverage of the specification. It is designed to help students get the most out of their revision. Information is broken down into manageable chunks and higher tier material is clearly differentiated.Essentials OCR Twenty First Century GCSE Biology offers clear and concise coverage of the specification. It is designed to help students get the most out of their revision. Information is broken down into manageable chunks and higher tier material is clearly differentiated.