Video Transcript
Why is a colored dye, a stain,
sometimes used when preparing a slide for viewing? (A) To make the cells look
larger. (B) To kill the cells so they do
not move. (C) To separate the cells so they
are easier to see. (D) To make transparent cells
visible. Or (E) to reduce the amount of
light passing through.
This question is asking about a
process used in preparing slides of specimens. To answer it correctly, let’s
review some key points about preparing slides for examination under the light
microscope.
To prepare a specimen for viewing
under the microscope, for example, some of your own cheek cells, it first needs to
be placed on a slide. The slide is usually made of glass
but can be made of other transparent materials to allow light to pass through
it. If you have got a sample of your
cheek cells on a cotton bud, you would wipe these onto your slide. You will not be able to see
anything as the cells are so small and they are transparent. So you have to remember where you
put them.
Over the area where you have placed
your cells, you need to place a drop of diluted methylene blue, which is a stain
used when looking at certain cells. Different stains are used for
different cells. For example, iodine solution can be
used for onion epidermis cells.
Once the stain has been added, you
can slowly and carefully lower the coverslip over your specimen. The coverslip is a very thin glass
square which also allows light through, which means you can then look at your
specimen under the microscope. The coverslip stops the specimen
from drying out, holds the specimen in place, and also protects the objective lens
from the stain. The coverslip has to be placed
carefully onto the specimen to prevent trapping air bubbles underneath it, which
would spoil the image you see of the specimen. The technique is to put the
coverslip at an angle of about 45 degrees on the edge of the solution on the slide,
then using a mounted needle or tweezers gently lower it down to cover the
specimen.
Any excess solution can be gently
wiped off the slide, taking care not to absorb all the stain which is under the
coverslip. The slide can now be placed on the
stage of the microscope. And you can examine it by looking
into the eyepiece. You will need to focus the image
carefully to see the detail. Hopefully, when you have it
focused, you will be able to see the main structures of your cell. The methylene blue stain added
during the preparation of the slide adds contrast and enables you to see the nucleus
and cell membrane clearly.
Now that we have reviewed the
technique of preparing a slide of a specimen to see under the microscope, we can
return to our question. This asks why is a colored dye, a
stain, sometimes used when preparing a slide for viewing. We now know the correct answer is
option (D). A colored dye, a stain, is used
when preparing a slide for viewing to make transparent cells visible.
