I would say doable (note, I never said easy) but ultimately it falls on your teacher if they feel like you could do it as long story short, if your teacher feels like you are at risk of failing your GCSE, they will not risk putting you in the higher tier exam if you can pass at foundation level.
Just to give an example, at A Level, the only grade I achieved was a D in Biology (I failed in both maths and chemistry) but managed to graduate from uni with a 2.1 and a Masters with Merit (both in biomedical science and ironically my specialism is in clinical biochemistry despite me failing chemistry at A level...).
It’s all down to how you revise and learning what works best for you as, long story short, my teacher’s revision and teaching methods didn’t help me in exam technique AT ALL, only when I got to uni did I manage to learn that… but again, that’s because I learned what was best for me rather than be taught a method which simply didn’t work for me! 🙂
Best of luck!