Electron Microscopy Overview

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Questions and Answers

What is a key characteristic of the Transmission Electron Microscope (TEM)?

  • Can only magnify up to 1,000 times.
  • Requires ultra-thin sections of 40-90nm. (correct)
  • Uses glass lenses to focus the beam of electrons.
  • Produces color images using an LED screen.

Which statement is true about Scanning Electron Microscopy (SEM)?

  • It produces images that show internal cellular structures.
  • The electron beam passes through the specimen.
  • Specimens are coated with a heavy metal like gold. (correct)
  • It requires a fluorescent screen to visualize the image.

What does 'electron lucent' refer to in the context of TEM imaging?

  • Sites where electrons pass easily through the tissue. (correct)
  • Areas that are visible as bright spots in the image.
  • Parts of the specimen that are electron dense.
  • Parts of the specimen that absorb electrons.

How does the imaging process of electron microscopes differ from light microscopes?

<p>Electron microscopes use an electron beam instead of light rays. (C)</p> Signup and view all the answers

What is the resolution power of a Transmission Electron Microscope (TEM)?

<p>Around 0.2nm. (C)</p> Signup and view all the answers

Which of the following best describes resolution in microscopy?

<p>The ability to show details clearly (B)</p> Signup and view all the answers

What is the primary purpose of a microscope in histology?

<p>To visualize cells that are too small for the naked eye (A)</p> Signup and view all the answers

Which of the following sequences accurately represents the metric conversions detailed in histology?

<p>1 μm = 1000 nm = 10 mm = 1 cm (D)</p> Signup and view all the answers

What is the function of the condenser in a light microscope?

<p>To focus light onto the specimen (B)</p> Signup and view all the answers

Which of the following lenses is responsible for the initial magnification in a light microscope?

<p>Objective lens (A)</p> Signup and view all the answers

Which type of microscope uses a beam of electrons for visualization?

<p>Electron microscope (B)</p> Signup and view all the answers

When carrying a microscope, how should it be supported?

<p>By the arm and the base (D)</p> Signup and view all the answers

In a light microscope, what role does the ocular lens play?

<p>To enlarge the image further and project it to the viewer (A)</p> Signup and view all the answers

What is the total magnification when using a 10x ocular lens with a low power objective lens?

<p>100x (D)</p> Signup and view all the answers

Which type of microscope is best suited for studying unstained, living cultured cells?

<p>Phase contrast microscope (A)</p> Signup and view all the answers

What is the primary use of a polarizing microscope?

<p>To study crystals and substances with ordered molecular arrangements (D)</p> Signup and view all the answers

Which type of microscopy utilizes laser light to achieve high resolution and sharp images?

<p>Confocal microscopy (C)</p> Signup and view all the answers

Why is an electron microscope more powerful than a light microscope?

<p>It employs beams of electrons for magnification (D)</p> Signup and view all the answers

What is the total magnification when using a 100x objective lens with a 10x ocular lens?

<p>1000x (A)</p> Signup and view all the answers

What is the limitation of the eyepiece lens in microscopes?

<p>It does not improve resolution (B)</p> Signup and view all the answers

Which microscope is primarily used for observing very small objects that cannot be seen by light microscopes?

<p>Electron microscope (B)</p> Signup and view all the answers

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Study Notes

Electron Microscopy

  • There are two main types of electron microscopes: Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM)
  • TEM has a resolution power of around 0.2nm and a magnification power of up to 400,000 times.
  • TEM uses a beam of electrons focused by electromagnetic lenses to create an image.
  • TEM images appear as shades of black and white, with electron-dense areas appearing black and electron-lucent areas appearing white.
  • Electron-lucent areas allow electrons to pass through easily, while electron-dense areas absorb or deflect electrons
  • TEM uses ultrathin tissue sections (40-90nm)
  • To view a TEM image, a fluorescent screen is needed to convert the energy of electrons into light
  • SEM uses a beam of electrons to scan the surface of a specimen coated with a heavy metal (gold)
  • The reflected electrons are collected by a detector to create a 3D black and white image on a TV screen.
  • SEM only shows the surface of a specimen because the electron beam does not pass through it.

Light Microscopy

  • Microscopes are used to view specimens too small to be seen with the naked eye.
  • Magnification refers to the degree of enlargement, and resolution refers to the ability to show details clearly.
  • The most important units of measurement in histology are:
    • centimeter (cm): 10 millimeters (mm)
    • millimeter (mm): 1000 micrometers (µm)
    • micrometer (μm): 1000 nanometers (nm)
    • nanometer (nm): 10 Angstroms (Ao)
  • Light microscopes use light to illuminate the specimen.
  • Electron microscopes use a beam of electrons to illuminate the specimen.
  • Brightfield microscopy, phase contrast microscopy, fluorescence microscopy, polarizing microscopy, and confocal microscopy are all types of light microscopy
  • TEM and SEM are types of electron microscopy.

Components of a Light Microscope

  • The frame consists of the base, arm, and stage.
  • The magnifying system consists of the lenses.
  • The illumination system provides the light source, which can be a mirror to reflect daylight or an electric lamp.
  • The condenser is located under the stage and collects and focuses a cone of light to illuminate the tissue slide.
  • The objective lens enlarges and projects the illuminated image of the object in the direction of the ocular lens.
  • The ocular lens (eyepiece) further magnifies the image projected by the objective lens and projects it onto the viewer's eye.

Microscope Magnification

  • To calculate the total magnification of a microscope: multiply the magnification of the ocular lens by the magnification of the objective lens.
  • The objective lenses provide higher magnification and resolving power than the ocular lens.
  • The ocular lens only enlarges the image already obtained by the objective lens, it does not improve resolution.
  • The total magnification of a light microscope depends on the objective lens used.

Special Types of Light Microscopes

  • Phase contrast and interference microscopes allow the study of unstained cells, which are transparent and colorless.
  • Fluorescence microscopes use fluorescent dyes to visualize specific structures or molecules.
  • Polarizing microscopes are used to study crystals and substances with repeating molecular arrangements, such as collagen, microtubules, and microfilaments.
  • Confocal microscopes use a laser to create high-resolution, sharp, 3D images.

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