Emergent properties, and why the level matters
Biology is organised into a hierarchy — molecules, organelles, cells, tissues, organs, organisms, populations, communities, ecosystems, biosphere — and the point of that list is not the order but what happens between the levels. Emergent properties are characteristics that appear at one level and cannot be found in the parts considered separately: a phospholipid does not have selective permeability, a bilayer does. Reductionism, breaking a system down to study its components, is how most of biochemistry was learned, but it is not sufficient on its own, which is why systems biology exists. Questions on this chapter almost always ask you to identify the level at which a stated property first appears.