Not worth it, for biology and chemistry, you just need to go through the specification, then pick your worst topics, after that, go through them, by making notes, then condense the most relevant stuff (that matches the spec) to a mindmap. It's okay if your notes become messy, so long as you can still gather information from it (I recommend highlighting then making a mindmap of it), repeating this helps you get it in your head. Once you've done that, go through questions, if you mess up, find out where you're going wrong and try understand the mark scheme (what you need). Videos explaining isn't as helpful as going through the work and making your own notes, it helps a lot more when trying to memorise what you need to know!