Final answer:
To enhance cell visualization under a microscope, a darkfield microscopy technique is employed by placing an opaque light stop above the illuminator, resulting in a dark background that makes transparent cells stand out.
Step-by-step explanation:
To change the background of a group of cells under a microscope, a technician may use a method like darkfield microscopy.
This technique involves inserting an opaque light stop above the illuminator, which enhances the contrast by creating a dark background.
As a result, the bacteria cells, which are nearly transparent in a brightfield microscope view, are made more visible as their light-scattering properties stand out against the dark background. These cells, which might be spherical and grouped in clusters, similar to grapes, become easier to observe and identify.
Another method is to use a fluorescent dye and a fluorescent microscope, which allows specific cellular structures to be visualized by emitting light of a specific wavelength.