The Science aptitude test is mostly Chemistry sort of things, there are some questions that are sort of the Chemistry equivalent of Literal Equations, except more you know, more chemistryish.
If you think you're going to have trouble with it, don't worry too much, because you can make it up with the rest of the tests, I think I got an average for it, but I went pretty well with the other ones so they let me in. Also on a separate note, if you get into EBSS you need to be able to learn on your own, because you're going to be in a class of around 70 for most of your subjects, so you're not going to get that same level of teacher interaction that you may have had at your current school. If you can it's very useful to form study groups with other students to review notes and classwork, or get a tutor, but they're super expensive, and at least I think having a tutor is morally questionable.