EPQWatch this thread
If you choose to do it there is quite a lot of work involved to do it well. If you do it in year 12 try and choose the right question in the least time, and work asap on it. The key thing is to work regularly on it, make sure you understand what is involved, maybe buy the textbooks on it, be organised and don't put it off. It is a challenge. Maybe choose a topic that helps with what you want to do at university and that you are interested in.
You don't want it to impact on your A levels so if you can cope with it so it doesn't, it may be worth it, especially if it helps with university.
Chemistry is hard, though, and Biology, so I would definitely get the EPQ work out of the way asap. There is a presentation too. I would do the log each week.
It is a good idea for the EPQ to look at planning time, use a time planner, show why you change your plan, show independent thinking and analysis in the product eg essay, correctly reference, show the process of choosing a title and why you may change ideas on the title, keep a detailed but relevant log, use a variety of relevant sources and evaluate them and look at potential bias etc, do aims and objectives and essay plans,etc. There are lots of things online which can help. Don't want to put you off though!
Just my opinion though so look into it thoroughly. Maybe buy a textbook and see if you can cope with the work. It is additional stress. Definitely work hard early and get it out of the way.
Topic - check there is no overlap with A levels. Maybe you could get an email from your teacher confirming this once you choose a topic, if you decide to do it just to be clear.