In what ways can you see microscopic organisms responding to stimuli? besides moving

The process of noticing environmental stimuli or stimuli arise from the body is called Sensation; the habit to pay less attention to a non-changing origin of stimulation promote change in responding to sensory events rather than perceiving constant stimulation.  The smallest noticeable difference of the  two stimuli-as stimuli get larger, differences must also become larger to be detected by an observer. 

well, i believe that the answer is 2. : 3