Can you go on to do a PHD straight after a BSc in a science?
In the US, none of the sciences expect either work experience or a MS prior to beginning a PhD. While in the process of getting your PhD, you will do all the coursework necessary for the MS so you can trivially get your MS along the way if you want it. (A lot of people never bother filling out the paperwork though.)
The only reason to get a MS separately first is if you are not a competitive candidate for a PhD program. (PhD programs are harder to get into.) That’s an undesirable route because you will end up needing to repeat most of the classes for your PhD program.
Sometimes humanities programs expect a MA first (hence some of the other answers) — but science programs never do.
Source: in a science phd program, with lots of friends in other science phd programs