GRE Subject Test: Biology : Understanding Light Microscopy

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Light Microscopy

To what power would a microscope magnify an object if the 10x low-power objective were in place and the microscope has a standard eyepiece?

Possible Answers:

1x

1000x

10000x

10x

100x

Correct answer:

100x

Explanation:

The occular, or eye piece, has a magnification power of 10x. If the 10x low-power objective were in place, the magnification would be multiplicative.

Example Question #2 : Understanding Light Microscopy

Which term is used to describe the smallest structure that can be seen by a light microscope?

Possible Answers:

Visual acuity

Resolving power

Optotype

Index of refraction

Optical transmission

Correct answer:

Resolving power

Explanation:

Optical transmission is the amount of light that passes through a laboratory specimen. It can be used to measure the concentration of components in the specimen. Optotype is the variable-sized type used in testing visual acuity. Visual acuity is a measure of the resolving power of the eye; the smallest type that can be seen at a distance. The index of refraction is defined as the speed of light in a vacuum divided by the speed of light in a medium. 

The resolving power of a light microscope is the smallest structure that can be seen, approximately 1 micrometer (a millionth of a meter) by the microscope.

Example Question #3 : Understanding Light Microscopy

When using a light microscope, the light waves that pass through or bounce off of a specimen are focused and magnified by which of the following?

Possible Answers:

Iris

Lens

Diaphgram

Fine focus

Occulars

Correct answer:

Lens

Explanation:

Light microscopes use lenses that range from 4x to 100x, are made of glass, and focus and magnify light rays.

The diaphragm regulates the amount of light that passes through an object being magnified. The iris controls the diameter of the beam of light entering the lens. The fine focus is used to move the objectives (lenses) to view objects clearly. The occulars are the lenses that one would look into to view the object. 

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