thinking about Second Bachelor's Degree

I’ve been dwelling over the possibility of a career change recently so now I am looking at going back to school for a second Bachelor degree. I should probably give you guys some of my background first before I get into the details of my question. I have a BA in Political Science from UW-Madison but never applied those skills to the current career I’m working in right now (IT).

Of the research I have done online, some people believe that grad school would be the best choice for someone who already has an undergrad degree. Is this true? My thought is to go back to school for Biology/Zoology but I can’t see myself going to grad school with the science/math skills I currently possess. During my undergraduate days, I did not take any more math or science than what was required for me to graduate. I’m afraid of not having the minimum knowledge needed to succeed at graduate level work. I understand that I could take stand-alone classes to prepare for grad school but would that really be equivalent to training gained from a typical 4-year science degree?

So that leads me to my ultimate question: Is it worth it for someone in my situation to go back for a BS? Or is grad school really the better route to take?