Can anyone suggest reference material on mathematics applied to biology, in particular the study of the behavior of say simple unicellular organisms or cells? Ideally the level of complexity should be aimed at a competent undergrad. Thank you.
Added: Also, I am wondering if there are any areas of biology where more abstract branches of mathematics is/can potentially be used -- that would be very interesting. By abstract I mean not just crunching through scores of differential equations, but using say geometry, group theory and whatnot.
The study of protein folding and protein structure uses a very wide variety of tools. First, there are statistical physics interpretations of the folding energy of a protein which heavily relies on theories from statistical mechanics and probability theory. Check out the introduction and few sections of this paper for a taste (the rest is pretty involved): http://arxiv.org/pdf/1002.5013v1.pdf
Second, there are techniques applied from differential geometry and group theory to study curvatures in protein folding and various structures that can arise, see here for an example: http://www.lmm.jussieu.fr/~neukirch/articles/GoHaNe_diff_geom_proteins_BioPhysRevLett_2008.pdf
Group theory as well has foreys in mathematical biology, see here: http://www.dur.ac.uk/mathematical.sciences/biomaths/events/iop08/