B3: Life on Earth Notes for the OCR GCSE Biology module: B3 – Life On Earth. These have been made according to the specification and cover all the relevant topics for examination in May/June. OCR GCSE B3 Notes: B3.1 Systems in balance – how do different species depend on each other? B3.2 How has life on Earth evolved? B3.3 What is the importance of biodiversity?