Movement is also caused by a gradual increase or decrease in tonal values, line size or shape size. So, movement grabs the eye-brain complex and causes a continual observer interaction with the image. The visual input is deciphered in the two brain modes and they work together to process the information. When you're framing, you want to try to eliminate things that distract from your point of interest. A distraction can be cropped in the darkroom or at the microscope.
Composition is a dominant contributor for expressing the content of the finished micrograph.
It causes direction and tensions, and they are suggested by the shapes. There is a principle called the lever principle and in microscopy, we are told to put our image in the center. But artists usually put it slightly off center and that grabs the initial interest. Usually scientific images are more restful, because they use the center. Images that have objects close together tend to want the objects to merge, like a magnetic attraction.