I recently returned from a conference at the Charles A. Dana Center in Austin, Texas, and there was much discussion concerning what knowledge was necessary in mathematics for students entering college. It seems relevant to ask this question for science as well, and I thought about it for the introductory biology and geology classes I've taught. For the life of me, I can't really think of any truly "necessary" prior knowledge one must have to do well in these courses.
Students must be able to think effectively in space and time. They must have a keen understanding of probability, and they must be able to distinguish useful information from psuedoscience. With these skills, I can teach them the details, but without them, I will spend most of my time trying to overcome misconceptions and poor reasoning.
There is certainly a "ton" of stuff for students to know in biology and geology, but this knowledge is just one tool needed to effectively ask new questions. Science literacy, both for future scientists and for voting citizens has more to do with the ability to use knowledge than with the quick recall of it.
We must teach for literacy!
This means we must teach the framework for understanding. We must teach the "big" ideas such as evolution and plate tectonics. We must teach reasoning skills, which means we must ask open-ended questions (this begs the topic for my next blog, Teach In Spite of Testing). We must avoid teaching knowledge as a checklist of facts, rather we must teach knowledge within context so that its usefulness is obvious.
When we talk about what knowledge students need to do well in math, we are also talking about skills. The information that accompanies these skills in math are harder to separate since the skills are more formulaic, but even for math, students who "get it" can learn faster than those who must "make up" for a lack of skills. The same is true for science. In math, we test for skills by asking for the information derived by them. The same logic does not apply to science. Recalling information does not necessarily indicate understanding.
This is why Hands-On, Minds-On project based science is the way to go! Read more about it at HUNSTEM's Constructivism page.