Yenta, from someone who graduated high school in the top 5% of the year (in terms of regent marks)I would suggest the following: the biologies, although you may find them hard at first, are mostly grasping infromation, and therefore do not necessarily require previous knowledge although it will definitely be harder for you. In terms of chemistry, the typical chem 101 courses assume you have mastered high school chemistry and the college couse builds on that. I would not advise you to take chem 101 without taking the equivalnet of a high school chem course beforehand. Your other option is being prepared to spend a lot of time at tutors and work super-hard.
Unless the professor dumbs it down, its not easy even after mastering high school chem.