Video Transcript
Why does a specimen observed using
a microscope need to be very thin? (A) Because there needs to be room
for the high-power lens. (B) Because it prevents the
specimen from drying up. (C) Because the specimen needs to
be dissolved in water. (D) Because it enables the slide to
be moved on the stage. Or (E) because light needs to be
able to pass through it.
This question is asking about the
preparation of a specimen so it can be seen under a microscope. To answer it, let’s review how the
microscope works and some key steps in the process of making slides.
If we know how the microscope
allows us to see our specimen in the first place, it will help us to understand the
preparation of the specimen to be viewed. So how does a light microscope
work? The light microscope usually uses
two magnifying lenses to enable a specimen to be examined in detail. A lens is a piece of transparent
material, usually glass, with curved edges, which bends light rays as they enter to
form an image of an object.
The slide, which has the specimen
on it, is placed on the stage under the first lens, called the objective lens. The light source below the stage
emits light, which passes through the slide, through the specimen, and into the
objective lens. The objective lens then bends the
light so a magnified image is formed. The light from this image then
passes through the second lens, the eyepiece lens, which magnifies the image
further. We then examine the image by
looking into the eyepiece.
So now let’s look at the steps
taken to prepare a slide of a specimen. For the specimen to be examined
under the microscope, it needs to be mounted onto a slide. The slide is usually made of glass,
as it needs to be transparent to let the light rays from the light source pass
through it. The specimen will be placed on the
slide with a drop of stain, such as iodine solution or methylene blue, to make the
transparent cells visible. A coverslip, which is a thin piece
of glass, will be placed on top of the specimen. It needs to be lowered onto the
specimen very carefully to avoid any air bubbles ruining the image.
Because the microscope relies on
the light rays to form the image, the specimen needs to be very thin. Otherwise, the light will not be
able to pass through it into the objective lens. This would result in a very dark
image with very little detail. Once the coverslip is in place, the
slide is ready to be examined.
Now that we have reviewed these key
facts, let’s return to our question. It asks, why does a specimen
observed using a microscope need to be very thin? We now know that the correct answer
is option (E): because light needs to be able to pass through it.
