BIOD 171: Module 3

BIOD 171: Module 3 questions with correct
answers


The microscope is perhaps the most: - answer-important resource for studying biology at
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the microscopic level.
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Micrometer - answer-(µm) is one-millionth of a meter and is commonly designated at 10-6
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m.
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Nanometer - answer-(nm) equals 10-9 m or one-billionth of a meter. f f f f f f f f f f




Two critical factors influence our ability to see an object: - answer-the resolution and the
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contrast.
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Resolution - answer-refers to the distance between two objects at which the objects still can
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be seen as separate.
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thus, the closer two objects are to each other, the greater the resolution requirement will be
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to maintain viewing the two objects as separate.
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Contrast - answer-is the difference in light absorbance between two areas (objects).
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the lower the contrast between an object and its background, the harder it will be to see that
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object.
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thus, the greater the contrast between two areas the easier it will be to visualize.
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Brightfield microscopes - answer-are the simplest form of light, or optical, microscopes.
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light, most often emitted from a standard halogen bulb, enters the microscope from the base
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(bottom) and is reflected via mirrors towards the sample.
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Before the light reaches the sample: - answer-it first passes through a condenser
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converging the light beams into a focused area on the sample.
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The Iris Diaphragm - answer-controls the amount of light that passes through the sample
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and into the objective lens.
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, Objective Lens - answer-is the lens closest to the sample and yields the greatest amount of
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magnification.
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(Note: The degree of magnification is directly proportional to the amount of light needed.
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Thus, to image samples clearly at higher magnifications, more light is required).
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Once light passes through the sample and the objective lens: - answer-it is directed through
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the ocular lens, or eyepiece, to your eye.
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the most common power of an ocular lens is 10x.
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for a microscope using two lenses (objective and ocular) the total magnification of a
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specimen is multiplicative.
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thus, a 40x objective and a 10x ocular result in a total magnification of 400x.
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In order to visualize cells: - answer-samples are most often stained with specific
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combinations of dyes that are taken up by the cell.
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Staining - answer-is often required due to the limitation of resolution on unstained cells
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because the flat and transparent regions of a cell may appear invisible under bright field
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conditions.
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by staining the cell with various dyes, these regions can become labeled and thus
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visualized.
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staining typically requires fixing the cells by heat or chemical methods before adding the
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dye.
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the cell fixation process produces its own challenges as it kills and may even distort the
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sample.
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Phase Contrast Microscopes - answer-have a distinct advantage over bright field
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microscopy in that they are often able to visualize certain structures that would otherwise be
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invisible.
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thus, a phase contrast microscope can provide detailed images of live cells without staining.
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By using specialized condensers and objectives a phase contrast microscope: - answer-
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amplifies the slight differences between cells and the surrounding medium (background) to
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make the cells highly distinguishable.
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for these reasons, phase contrast microscopy can be used to visualize cell movements
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(motility), such as swimming or gliding, without altering the cell morphology commonly
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brought about from treating the cells with a fixing agent.
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