Physics departments have long been providing service courses for premedical students and biology majors. But in the past few decades, the life sciences have grown explosively as new techniques, new instruments, and a growing understanding of biological mechanisms have enabled biologists to better understand the physiochemical processes of life at all scales, from the molecular to the ecological. Quantitative measurements and modeling are emerging as key biological tools. As a result, biologists are demanding more effective and relevant undergraduate service classes in math, chemistry, and physics to help prepare students for the new, more quantitative life sciences. In general, physicists stress reasoning from a few fundamental principles--usually mathematically formulated--and seek to build understanding from the simplest possible models. They view the world quantitatively and pay much attention to constraints, such as conservation laws, that hold regardless of a system's internal details. Biologists, on the other hand, focus on real examples and emphasize structure–function relationships, with less emphasis on quantitative reasoning. The systems they deal with are almost always highly complex, with many interacting parts that lead to emergent phenomena. This paper examines ways in which introductory physics courses for life science majors can bridge the gap by promoting specific skills such as building simple quantitative models, connecting equations to physical meaning, integrating multiple representations, estimating, and practice with scaling.