BIO 171 Module 3 Exam Questions and Answers- Portage
Learning
Define the measurements micrometer and nanometer.ANS A micrometer (µm) is
defined as
... [Show More] being one-millionth of a meter and is commonly designated at 10-6 meters. A
nanometer (nm) equals 10-9 m or one-billionth of a meter.
What are the two critical factors that influence your ability to see an object?ANS
Resolution and contrast. Resolution refers to the distance between two objects at which
the objects still can be seen as separate. Poor or low resolution means two (or more)
objects may appear as one. The contrast is the difference in light absorbance between
two objects. Poor contrast gives a high background and makes the visualization of
multiple objects difficult. For instance, trying to identify 2 dark colored objects at night
(low light = low contrast) versus the same 2 objects in the middle of a sunny afternoon
(bright light against 2 dark objects = high contrast).
If you wish to increase the amount of light going into a microscope, what part would you
adjust?ANS The iris diaphragm controls the amount of light that passes through the
sample and into the objective lens. Thus, as you open the iris more light is permitted to
pass through to illuminate the sample.
As light passes through a microscope, what is the last piece that light passes before
reaching your eyes?ANS Once light passes through the sample and the objective lens
it is directed through the ocular lens, or eyepiece, directly into your eye.
How is the total magnification of an object calculated?ANS Total magnification is
calculated by multiplying the power of the objective and the power of the eyepiece. For
instance, a 40x objective with a 10x eyepiece would make an object appear (40 x 10)
400 times larger (400x).
What is one limitation of fixing your sample?ANS Fixation requires you to irreversibly
kill your sample. Thus, determining the motility (cell movement) of a sample is
impossible. Fixation also runs the risk of distorting the specimen shape and
arrangement.
Phase-contrast microscopy provided what benefits to imaging?ANS Phase contrast
microscope can provide detailed images of live cells without staining. By using
specialized condensers and objectives, a phase contrast microscope amplifies the slight
differences between cells and the surrounding medium (background) to make the cells
highly distinguishable.
What is the distinguishing feature of dark field microscopy?ANS Unlike bright field or
phase contrast microscopy where light passes directly through the sample, dark field
microscopy reflects light off of the specimen at an angle. The resulting image is an
exceptionally dark background and a vibrant specimen.
Unlike brightfield microscope, fluorescence microscopes illumin [Show Less]