While GRE scores are certainly important, so is your research experience. If your GPA is above a 3.0 and your GRE scores meet the minimum requirements, your app will be looked at. What it really comes down to is your research experience and how competitive your scores and gpa is. Personally, my GRE scores sucked, but schools are still giving me a shot because I have a publication and 2 years of research. My grades were pretty good too, which certainly helps.
As for a Masters or not, I would think about this. What do you really want to do with your life? Do you want to teach, work for a pharmaceutical company, or be a professional researcher? People that hold a MS in the biological sciences don't need a PhD to work for a company, and it can save you time. You could also teach in a high school or community college with a masters degree. However, master's programs aren't really funded well and can leave you in debt. A PhD is more versatile but takes longer to achieve. With a PhD you could: teach, work for a compnay, or become a full tenured professor, or do research. I feel that many people don't ask themselves these questions, but you should.