For self-assessment questions, with exercises and discussions, just click on ‘The chemicals of living cells’ (qu.13 onwards) at Biology GCSE & IGCSE Question Bank. A powerpoint (the chemicals of living cells) can be downloaded from the same site here. The s-cool revision site lets you revise the topic, summarizes the topic and tests you on it. GCSE Bitesize has revision pages (that take you through the topic), a test and an activity.
Science Bank 8: you just need Part 3 (from 9m 55s) – Enzymes – biological catalysts & factors affecting their rate:
A simple animated tutorial from McGraw Hill Education on how enzymes work.
Mr W sings ‘Enzymes!’:
IGCSE Biology: Coursebook, chapter 5, pp.39 – 44