I thought the reformed A-Level courses were 2-year courses, and that Sixth Form students wouldn't be able to drop any subjects? If not, that's my mistake.
As for dropping a subject, I would think that it depends on what other subjects you're taking and what the workload would be like, especially if you're going to be doing an EPQ on top of that. I'm a Year 13 student, so I'm doing the current A-Levels and 3 subjects (there are some students who stick with 4, but not many). I'm taking Biology as one of my subjects. Yes, it is a hard subject; as you say, h3rmit, you can't just blag your way through it. In the exam, you need to put down the correct key terms that the examiner wants. You may put down a synonymous term or explain it perfectly, but if it's not the word that they want, you don't get the mark.
Also, in the Unit 5 exam, you have to write a synoptic essay on a subject spanning both AS and A2 Biology. I'm not saying all this to scare you off from carrying on with Biology into Year 13; I'm just telling it like it is so you know what it'd be like