Microscopes/Magnification Flashcards

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1
Q

Magnification equation

A

Image/Object

Remember to convert to correct units

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2
Q

Magnification

A

Being able to enlarge something in appearance.

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3
Q

Resolution

A

Ability to distinguish points close together.

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4
Q

The two types of electron microscopes

A

Transmission electron microscopes, Scanning electron microscopes

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5
Q

Transmission electron microscope

A

They produce a black and white image. It results in a 2-D image. It consists of an electron gun that produces a beam of electron that is focused onto the specimen by a condenser electromagnet. The beam passes through a thin section of the specimen. Parts of the specimen absorb electrons and therefore appear dark. Other parts allow the electrons to pass through so they appear bright. The image produces a photomicrograph.

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6
Q

The main limitations of TEM

A

The whole system must be in a vacuum so living specimens cannot be observed. A complex staining process is required. The specimen must be extremely thin to allow the electrons to penetrate the specimen. This results in a 2-D image. The image may contain artefacts.

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7
Q

Scanning electron microscopes

A

It produces a 3-D image. The SEM directs a beam of electrons onto the specimen from above rather than from below like a TEM. The electrons are scattered by the specimen. Computer analysis allows a 3-D image to be seen.

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8
Q

Benefits of electron microscopes over light (optical) microscopes

A

They have a higher resolution than light microscopes because the electron beam has a shorter wavelength. Therefore it can see smaller objects than light microscopes because of a higher resolving power.

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9
Q

What should the object be in a light microscope?

A

The object should be thin to be viewed under a microscope. It should be a single layer of cells thick to allow the light to pass through.

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10
Q

The eye piece graticule

A

It is a glass disc fitted into the eyepiece of the microscope. The absolute size is not important as this is what will be calibrated.

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11
Q

The stage micrometer

A

It I used to calibrate the eyepiece graticule. A stage micrometer consists of a microscope slide on which is engraved a fine and accurate scale. This is used to calibrate the eyepiece graticule.

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12
Q

Stages of using an eyepiece graticule (e.g. using stomata)

A

Measure each stoma using the eyepiece graticule.
Calibrate the eyepiece graticule against the stage micrometer using a ruler
Take a number of measurements to calculate the mean.

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13
Q

Benefits of a light microscope over an electron microscope

A

It can look at living cells because they don’t have to be in a vacuum.
They can look at colour images.

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14
Q

Artefacts

A

These are things that result from the way the specimen is prepared. They are not part of the natural specimen.

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