Biology has a lot of content. It's not terribly hard if you have a good memory/actually work hard, but the amount can scare people sometimes, so just don't panic if you find it to be a big jump. I found it really useful to review my notes after every lesson, so that I'm revising and memorizing the content as I go along, as there's too much to memorize if you leave it all for the month or so before the exam. I usually took notes from the textbook after the lesson to go with the notes taken in the lesson, and every week or 2 I'd condense all my notes in a poster.
Chemistry is a big jump - you can't rely on just memorizing information like GCSE, you have to actually understand it. Just make sure that you understand the GCSE content and was not just memorizing it mindlessly for the exam.