Every college requires applicants to have completed a core high school curriculum, but the specifics can vary greatly from school to school. On the science front, the majority of selective colleges want to see at least two years of a science, usually selected from biology, chemistry and physics. Some schools will recommend or require three or even four years of science.
As you plan your courses and prepare for college, check out this new article on science requirements for college applicants. You don't want to discover during your senior year that you don't have the coursework you'll need to get into your top choice colleges.
If you're applying to highly selective colleges, keep in mind that the most impressive applicants will typically have AP or IB coursework in the sciences.