Keeping in mind with OP's original design concept, of pencil sketches as background and the numerous ideas from the community, I went hunting in google images and found a few sketches, perhaps more in line with Biology ?. 

I am not a graphics designer, so I don't know if these are useful, but figured I'll post them anyway.


![enter image description here][1]


![enter image description here][2]

![enter image description here][3]

We can perhaps remove the chemistry elements from here and instead add elements by @rg255, @terdon and @fileunderwater ? I'll keep updating as I find more. 


  [1]: https://i.sstatic.net/oqro1.jpg
  [2]: https://i.sstatic.net/l7yvy.jpg
  [3]: https://i.sstatic.net/kVa3Q.jpg