You’re a quantitative person and you want to learn biology. My friend, you are in a difficult situation. If you really want to learn how biology works in a big-picture sense, as opposed to cutting yourself a very narrow slice of the great biological pie, then you have a challenging road ahead of you. Fortunately, many have walked it before you, and I want to give you some advice based on my own experiences. I should say at the outset that my own learning has focused mostly on the cell-biology part of the pie – not physiology, zoology, ecology, … and so my comments here refer to learning cell biology.
The scary thing is that I have been at this for almost 20 years (very part-time admittedly) and I would never dare to call myself a cell biologist. But I think it’s fair to say that by now I have a decent sense of what I know and what I don’t know. I will never be able to draw out the Krebs cycle, but I have a qualitative sense of its purpose and importance, as well as of general principles of cycles and catalyzed reactions in biochemistry. Not that impressive, I know, but I’m proud of it anyway.