I went straight from undergrad biological sciences (Biochemistry) to a PhD in biophysics. I imagine it was even more off a jump into the deep end for me as my undergrad dissertation was bioinformatics based, so the only actual lab experience I had was from an 8 week summer placemnt after 2nd year, and I actually knew very little about biophysics. For me, it felt a little bit like I'd just jumped into the deep end at the start, but now at 9 months in and having just finished my first year review, I don't feel behind at all. It's like, I spent months constantly worrying about not being good enough and not being independent enough and not knowing what I'm doing, and then one day I just was halfway through an experiment and realised that I actually did know what I was doing and I was doing really well with my project. I have also spoken to other PhD students who did a masters in a relevant field, or did relevant work experience for a couple years before their PhD, and everyone feels the same. When you are focussed on a project every day, you will learn things really quickly. An MRes might get you more used to the 9-5 mon-fri after undergrad, but an MRes is basically the first year of a PhD anyway, so you may as well go straight forthe PhD where you will actually get paid to be there