Question Video: Preparing Bacterial Samples to View with a Light Microscope Biology

Video Transcript

Bacterial samples are almost transparent under the regular light microscope. What preparation could be done to the sample prior to examination for it to be viewed clearly? (A) Squeezing the sample before examination. (B) Staining the sample before examination. (C) Adding an excessive amount of water to the sample before examination. (D) Drying the sample before examination.

This question is asking us about the preparation of slides so that bacterial samples can be visualized under a light microscope. So, to answer this question, we need to review how light microscopy works to visualize objects like bacterial samples.

A light microscope works by projecting light up through the sample, which reaches our eye after traveling through two magnifying lenses called the objective lens and the eyepiece. However, as the question stated, most bacterial cells are colorless. So they can be hard to visualize with a light microscope.

To more easily distinguish between cells or structures within a cell, stains and dyes can be applied to the cell before it is placed under the light microscope. Stains and dyes are taken up with different degrees by different cellular components. This increases the contrast between the different components of a cell, making them easier to identify.

One example of a stain is methylene blue, which binds to the negatively charged cellular components in the cytoplasm or the nucleus. Another example of a stain is Congo red, which is repelled by the negatively charged cytoplasm and so mostly leaves the cells unstained. Instead, it stains the extracellular structures surrounding the cells, making the cells easier to distinguish. Congo red can also stain cell walls of an organism like plants and fungi or the membranes of certain bacterial cells.

When hematoxylin and eosin stains are used, the hematoxylin stains the nucleus with a purplish-blue color and the eosin stains the extracellular matrix and the cytoplasm with a pink color. So, stains and dyes allow the scientist using the microscope to be able to see structures and cells that would otherwise be transparent.

With this information, we can answer the question. Therefore, the preparation that could be done to the sample for it to be viewed clearly is staining the sample before examination.