For self-assessment questions, with exercises and discussions, just click on the correct topic at Biology GCSE & IGCSE Question Bank. A powerpoint can be downloaded from the same site here. The s-cool revision site lets you revise the topic, summarizes the topic & tests you on it. Skoool gives you a lesson, including progress questions, for each Biology topic but you’ll need sound on for it. GCSE Bitesize has revision pages (that take you through the topic), a test and an activity.
What is aerobic respiration? a short (51s) introductory video from Clipbank.
Science Bank 8 (Biological Reactions): you only need Part 2 – Respiration (from 5m 20s to 9m 55s):
Dr. Kiki talks about how fermentation works and whips up some home made ginger ale at the end.