You will register on SOLAR to iSci-1A24 as a whole... though it is 24 credits, it is considered one "course." And this will be reserved for you, so do not worry about 'losing a spot.' As future reference, if a course is required for your specialization/major/concentration (so long as you have been accepted for that specialization/major/concentration), no matter what you must get a spot in it... (this is where administration will bend their back over to help you).
So really, if you are taking a 100% course load, you will only have 2 or 3 courses signed up to on SOLAR (depending if your elective is full year or two half years). And even if you are planning to drop an elective during the school year, still sign up for one, so you have the spot in case you choose to keep it.
Also you should be signed up to Science 1A00 (and the Health Sci skills too, I forget the code)... but because they are not actually "courses" in the true sense, you do not have to worry about getting a spot, as you will be allowed to sign up for both of those at anytime no matter what as well, it's more of a formality than anything.