For self-assessment questions, with exercises and discussions, just click on the correct topic at Biology GCSE & IGCSE Question Bank. Powerpoints 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.
What’s in a molecule? – The science of macaroni salad from TED-Ed (3m 15s).
This powerpoint covers both Plant and Animal nutrition: