State one reason a student would use this technique during a scientific investigation

One reason why any student would use this when they are doing a scientific investigation is to add a solution to the slide without removing the coverslip. This is not the picture that goes with the question, so there may be some sort of mix-up you had. The picture should show a slide with a vial putting liquid on it. 

This is what i found on google “phytoplankton, tiny organisms that live in the ocean, are autotrophs. some types of bacteria are autotrophs. most autotrophs use a process called photosynthesis to make their food.” i hope this you for what your looking for