GRE Subject Test: Biology : Understanding Electron Microscopy

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

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Example Questions

Example Question #4 : Lab Techniques

Which of the following is used to focus the electrons when using an electron microscope?

Possible Answers:

Reticle

Laser

Phase plate

Lens

Magnetic field

Correct answer:

Magnetic field

Explanation:

Electron microscopes use beams of electrons instead of light. The electrons are focused by magnetic fields rather than by lenses.

A phase plate is used with a light microscope to view details of objects characterized by differences in refractive index and, as such, have a difference in brightness or color. Tissues deep within the body can be imaged using the technique of multiphoton microscopy, in which photons are directed into tissues by an infrared laser. The reticle is a tiny grid pattern inserted into the eyepiece lens. It is used to make measurements of objects seen through the lens. 

Example Question #3 : Microscopy

Which of the following is not a type of the electron microscope?

Possible Answers:

Retraction electron microscope 

Transmission electron microscope

Scanning electron microscope 

Reflection electron microscope 

Scanning transmission electron microscope 

Correct answer:

Retraction electron microscope 

Explanation:

The incorrect answer is retraction electron microscope. Transmission electron microscope is the simplest type by using a high voltage electron beam to formulate an image. Scanning electron microscopes produces an image through a scanning electron beam. Reflection electron microscopes use an electron beam that scatters when it hits a specimen, the image is then compiled from the scattered electron pattern. Scanning transmission electron microscopes uses a thin ray of electrons that scatters through the specimen to resolve the image. 

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