I want to answer your question about having students look at something, specifically animals, and not having a zoo readily available to draw from observation.
I fight this fight daily. I 'make' my student reference from at least 4-6 images, and then they must produce a 'franken' animal, that is to say an animal based on the referencing that has parts of each of the 4-6 images, but is NOT copied directly from 1 image. After looking at 6 elephants, students should be able to draw their ears for example, without copying exactly. My problem with students copying images is that those images belong to the photographer who initially took the photograph. The photographer made the initial aesthetic decisions to take the 'work'. Secondly, working from observation challenges the student to capture everything from texture to light sources, whereby when working from a photograph all of these 'problems' and 'observation skills' have already been solved. One of my sketchbook assignments for example, is to draw the family pet ,or your sister/brother if you don't have one ;-) to let them know that drawing from observation is a 'whole other ball game'.
I also have students reference environments to place their animals in, and to make thesis statements about their placements and their intended light sources, so that I let them know that we are creating a whole new 'scene'.