Final answer:
To prepare cheek cells for microscopic examination in a biology practical, the stain called safranin should be used after heat-fixing the cells on a slide, to enhance the visibility of cell structures like the membrane and nucleus.
Step-by-step explanation:
When preparing cheek cells to observe under a microscope in biology class, you should add a stain to the cells to increase contrast and visibility. Specifically, the recommended stain to use is safranin, which is a pinkish-red colored dye. After heat-fixing the smear of cheek cells on a slide, apply safranin to the sample. This stain will help to make the cell structures, such as the membrane and nucleus, more visible when viewed under the microscope. In a broader context, different types of stains are utilized in microscopy, such as those used for Gram staining, which can differentiate bacteria based on their cell wall properties.