can you do architecture using a biomedical science degree

Obviously no.

what degree will i need?

A RIBA Part I undergraduate architecture degree to meet the first stage requirements. Then you will need a RIBA Part II postgraduate architecture degree (usually called an MArch) to meet the second stage requirements, along with a period in an approved work post in the sector and completion of the final requirements to achieve Part III (usually a postgraduate diploma; I believe this is commonly done concurrently with the 24 months of professional experience following the Part II postgraduate course). It takes an absolute minimum of 7 years to fully qualify as an architect and only through doing those appropriate RIBA accredited and ARB prescribed courses.

I would suggest reading the RIBA guidance on this here: https://www.architecture.com/education-cpd-and-careers/how-to-become-an-architect

I’m currently taking a gap year after finishing a levels. my results were mediocre and i still am not sure what i want to do. i’m a very creative person and want to study something that includes a bit of art in it. initially i was going to study biomedical science and then try to study dentistry with that but now i’m not sure if that will be fully suited for me as biology isn’t my strong suit. my question is if i choose to study biomedical science and get a degree with that, is it possible to pursue architecture?