In a nutshell - Scope and first things
As you say, plenty of material to draw on for cells. In fact that is probably the main problem. there is too much material to draw on and we have to distill out the points that are most relevant to vet nurses and present them in the clearest way. I have a fairy good feel for what vet nurses have to know re cell biology but when adapting the material for human biology the emphasis seems to be different. For instance I have had issue with how little genetics vet nurses are exposed to while in bioscience for nursing there is much more material on DNA structure, cell division etc.
Fair enough Ruth --
I'm not querying the content integrity of the selection of diagrams -- but rather the formats in which diagrams are created and stored. Sourcing existing svg graphics means that we can save time, energy and money - moreover, they can easily be edited for alternative scenarios.
Like I said -- I have no expertise in your content area - just trying to give a few tips on how to improve the productivity of your content development processes in a contemporary environment.