I haven't read freshman biology for a very long time, so I don't know what the current textbooks are, but it is basically like physics or maths - you can use the equivalent of Stewart :) OK, kidding, I never read Stewart, let's say a good book like Young or Halliday and Resnick. If a free online version is available in the PubMed library, I have listed it, but they are hard to read in that format, so I should say those also exist as regular books.
Personal favourites
https://www.amazon.com/dp/0716730278/?tag=pfamazon01-20 (Maybe outdated in specifics, if you follow Ygggdrasil's posts about domains of life. However, Lynn Margulis proposed endosymbiosis, an example of first rate biological thinking.)
https://www.amazon.com/dp/0192191942/?tag=pfamazon01-20 (Old pop sci book, again maybe outdated on specifics)
https://www.amazon.com/dp/0716728664/?tag=pfamazon01-20 (One can also get the cheaper earlier editions. I read the second edition.)
http://faculty.uca.edu/benw/biol4415/papers/mickey.pdf (Classic by Gould)
Freshman biology
https://www.amazon.com/dp/0321775651/?tag=pfamazon01-20
Evolution
https://www.amazon.com/dp/1405103450/?tag=pfamazon01-20
https://www.amazon.com/dp/1605351156/?tag=pfamazon01-20
Genetics
http://www.ncbi.nlm.nih.gov/books/NBK21766/
Cell and Molecular Biology
http://www.ncbi.nlm.nih.gov/books/NBK9839/
http://www.ncbi.nlm.nih.gov/books/NBK21475/
http://www.ncbi.nlm.nih.gov/books/NBK21054/
Developmental biology
http://www.ncbi.nlm.nih.gov/books/NBK9983/
Just in case you would like to see "quantum field theory" in action in biology, here is
http://arxiv.org/abs/0704.1650
The Kuramoto model is intended to capture some aspects of fireflies.
For advice on a mathematician doing biology, you may also like to write to Nancy Kopell
http://math.bu.edu/people/nk/. I have never met her, but her work is fabulous and related to stuff I work on.