From what I understand, each subject has its own teachers, so Chemistry, Biology and Sciences...
Three teachers right off the bat.
Really, it's good for so many jobs to be available and all...
Departments!
Sciences seems like a very broad subject, since most high school teachers usually have a specialisation they teach. They might teach combined Sciences for lower secondary, but for upper secondary they usually teach what they're specialised in, like Physics, Chemistry, Biology, Environmental Science, Computer Science etc.
My school has this cool thing where you can get optional topics based on your subject, kinda like specialisations. So for example, if you take Chemistry, you can go a whole bunch of different ways. You can take Food Chemistry, Environmental Chemistry, Medicinal Chemistry, Material Science, Chemistry of Energy Production, Biochemistry... the list could go on and on. Same thing goes for all the other subjects too! In Math, you can take the kind of math topics that would be more appropriate for your future career. You can take university-level Calculus if you're doing something science-based like Physics or Engineering, you can take higher Statistics if you're going into that kind of field, or Discrete Maths if you're doing Computer Science or Algorithms.
Basically, options are good. You can have multiple teachers for one subject then.