Video Transcript
What is the correct sequence of
steps for viewing a specimen using a microscope? (A) Select high-power objective
then place slide on stage then turn coarse focus then turn fine focus then select
medium-power objective. (B) Select low-power objective then
place slide on stage then turn coarse focus then turn fine focus then select
medium-power objective. (C) Select high-power objective
then place slide on stage then turn fine focus then turn coarse focus then select
medium-power objective. (D) Select low-power objective then
place slide on stage then turn fine focus then turn coarse focus then select
medium-power objective. Or (E) select low-power objective
then place slide on stage then turn fine focus then turn coarse focus then select
high-power objective.
When we want to view specimens,
like unicellular organisms, using a microscope, there is a specific order of events
that we need to follow to observe them most effectively and clearly. First, we make sure that the
lowest-power objective lens is selected and clicked into place above the stage. On most light microscopes, this
will be the 10 times objective lens. It’s important to start with the
lowest magnification possible so you can easily find the specimen on the slide and
gradually focus it before increasing the magnification to see the specimen more
closely. In fact, if you use the high-power
objective lens first, it may even come into contact with the slide and potentially
damage either the slide, the microscope, or both.
Knowing this, we can already
eliminate options (A) and (C) as they both suggest using the high-power objective
lens first.
Then, having prepared our slide
containing a specimen in advance, we can place the slide upon the stage, just below
this low-power objective lens. While looking down the eyepiece of
the microscope, you can then turn the coarse-focus knob until the contents of the
slide become clearer and more distinct. After this, you can use the
smaller, fine-focus knob to make the specimen as clear as possible. It’s important to use the coarse
knob first, as this moves the stage containing the slide more quickly to bring the
specimen into focus. It could take a much longer time to
achieve the degree of focus you want if you only used the fine-focus knob.
Knowing this, we can eliminate
options (D) and (E), as they both suggest using the fine-focus knob before the
coarse-focus knob.
Once we’ve achieved the desired
degree of clarity, we can then increase the magnification. We do this by selecting the
medium-power objective lens and clicking it into place above the slide. Then, we focus the specimen again
and view it nice and closely.
Therefore, the correct answer to
this question is (B). Select low-power objective then
place slide on stage then turn coarse focus then turn fine focus then select
medium-power objective.
