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.