I have to say even you want to take courses in CC and UCLA concurrently, it's still challenging. Because science courses in CC usually come with lab, if you have to go to places to places then the time may conflict. And don't even assume that science class in CC will be much easier because you're aiming "A"s not just passing the class. It's 93% out of 100. (for some CC, they will curve the grade but it's still very hard to get A)
A lot of pharm schools accept CC transcript but USC prefers 4yrs university. If you really want to go to pharmacy, you can choose other minor or 2nd major rather than poli sci. or on first quarter you can take one or two chem/bio classes to have a feeling of the difficulty. But fairly speaking, if you spend some time in studying, it's not hard to get good grades in UCLA except lab courses.