One distinguishing feature of biology seems to be that it is always possible to examine a process in a greater level of detail, whether it is cellular respiration or blood clotting or evolution.
You can say something simple like “DNA contains genes, which are instructions for making proteins using ribosomes” but there are masses of additional complexity behind the process of protein synthesis, and there is far more that DNA does. For instance, the DNA molecule is both a store of information (base pairs) and a physical machine that does things like replication during mitosis.
A recent abstract from Science highlights some of this:
A Time and a Place for Hox Genes
Patterning of the mammalian body relies on the stepwise transcriptional activation of Hox genes. Noordermeer et al. (p. 222) show that this process involves a dynamic transition in the global architecture of Hox gene clusters, with each gene transitioning, one after the other, from a negative three-dimensional (3D) compartment to an active compartment. This bimodal configuration parallels the distribution of distinct chromatin marks, suggesting the existence of a link between the presence of chromatin domains and the formation of 3D chromosomal structures. This model for Hox gene activation would ensure the proper sequence in the transcriptional activation of Hox genes within each gene cluster.
Unless we eventually develop tools that map out every biological process down to the functioning of individual atoms (which we have basically done for processes like photosynthesis), there will always be more to learn about how living things operate.
If anyone wants to read a detailed account of the molecular biology of photosynthesis, I really enjoyed the first third of Oliver Morton’s: Eating the Sun: How Plants Power the Planet.
I enjoyed the whole book, but only the first third is about molecular biology. The rest of the book is a more general (and still very interesting) discussion of the general importance of photosynthesis and the carbon cycle.
Another reason biology contains infinite complexity is that new systems emerge at higher levels of resolution.
*I realize that phrasing was ambiguous. By “higher” resolution I meant looking at things on a bigger scale. I probably should have actually said “lower” resolution.