In the car tonight, the boy mentioned that in this first day the teacher covered various levels of complexity. Atoms beget molecules, then there are cells and tissues which are organized into organisms (organ might have been in there) and communities. I looked in the book (Exploring Life by Campbell, Williamson and Heyden, from Prentice Hall, copyright 2006 ) as well, and as expected it follows these lines. Which got me thinking: they're missing a critical one.
Now, any time you try to divide the natural world with human boundaries, issues will arise. Atoms really are a natural unit, but particularly in biology one shouldn't be too fixated on herding the world within fixed walls. But categories are useful for helping to tame the complexity of life.
The level that struck me as universal to life and something worth its own mention? Complexes. Thinking about proteins being enzymes that accelerate chemistry should be pretty mind -blowing, but that these proteins are often assembled into exquisitely featured architectures -- and dynamic ones too. Ribosomes, proteasomes, replication complexes, signalling complexes, the machinery to make antibiotics -- this is a key.
Studying complexes is also a hot field, partly because of the increased understanding of how many proteins are ordered into assemblages but especially because the tools to study complexes have been getting so much better. CryoEM imaging of huge macromolecular ensembles is opening new avenues for understanding them, while advancement in proteomics makes discovering the members of complexes so much more straightforward -- as well as providing insights into how membership can shift during their lifespan. Plus X-ray crystallography keeps getting better at analyzing large proteins and collections of proteins, and computation methods are getting better for generating hypothetical structures of complexes given some structural information.
The explosion of CryoEM, X-ray crystallographic and similar images would also make great textbook imagery, showing off how elaborate a shape a structure can hold. Not only is this important, in my opinion, for illustrating a key point about biology, but perhaps such images can catch the imaginations of students who go into class thinking "science is not for me".