Question

What is the purpose of heat fixing a slide?

A) To promote bacterial growth
B) To stain the sample
C) To kill bacteria on the slide
D) To preserve the sample for long-term storage

Answer 1

The purpose of heat fixing a slide is to kill bacteria and secure them to the slide for staining and microscopic observation, not for promoting growth or long-term storage.

Step-by-step explanation:

The purpose of heat fixing a slide is C) To kill bacteria on the slide, which also helps to adhere the cells to the slide surface and preserve the integrity of their cellular components for observation under a microscope. Heat fixing involves evenly spreading a bacterial culture in a thin layer on a slide, then passing the slide through a flame or over a slide warmer. This process not only secures the bacteria to the slide but also stops their movement and metabolism, making it easier to observe and stain the microorganisms. After heat fixing, the sample can be stained with various dyes, such as cationic dyes like methylene blue or crystal violet that bind to the bacterial cells, or anionic dyes like eosin which are repelled by the cells. These dyes increase contrast, making cellular structures visible under a microscope. Heat fixing is not for promoting bacterial growth or long-term storage of samples; those processes involve different techniques.