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As-Level Biology > Cells - Cell structure - 3.2.1.5 - Light and Electron Microscopes > Flashcards

Cells - Cell structure - 3.2.1.5 - Light and Electron Microscopes Flashcards

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1
Q

What you see when looking through a microscope is called the

A

Image

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2
Q

What are the disadvantages of a light microscope?

A
  • Low resolution due to ‘longer’ wavelength of light.
  • Low magnification (X1,250 max)
  • Thin specimens may not represent true specimen.
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3
Q

What are the advantages of a light microscope?

A
  • Easy to use (no special training required)
  • Cheap (
  • True colour images but may sometimes require staining.
  • Can observe live specimens
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4
Q

Define microscope resolving power.

A

The ability of a microscope to differentiate between 2 close together objects.

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5
Q

What is another term for resolution?

A

Resolving power

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6
Q

What is meant by magnification?

A

How much bigger an object looks under a microscope.

Magnification = Image Size ÷ Actual Size

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7
Q

What are the advantages of a transmission electron microscope (TEM)?

A
  • High resolving power (0.1 nm)
  • High magnification (X500, 000)
  • Provides detailed images of internal structures of cells.
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8
Q

Name the 3 main microscopes used by scientists.

A
  1. Light microscope
  2. Scanning electron microscope (SEM)
  3. Transmission electron microscope (TEM)
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9
Q

What are the advantages of a scanning electron microscope?

A
  • High resolution (20 nm)
  • High magnification (X200, 000)
  • 3D images
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10
Q

Why do electron microscopes have a greater resolving power than light microscopes?

A
  • They use electrons to interact with the specimen.
  • Electrons have a shorter wavelength so interact more witht he specimen.
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11
Q

What are the disadvantages of a transmission election microscope (TEM)?

A
  • Special training is required before use.
  • Samples must be dead as electrons are fired through a vacuum and stains containing heavy elements are used.
  • ‘Artefacts’ can be present in image from staining process.
  • Sample must be 1 cell thick to allow electrons to penetrate specimen.
  • Black and white images only so false colour must be used.
  • 2D images - 3D possible but complicated and slower than SEM.
  • High cost
  • High energy electron beams can destroy the specimen.
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12
Q

What is the resolving power of a light microscope and what does this mean?

A

2 µm

It can differentiate between objects up to that distance apart.

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13
Q

What are the disadvantages of a scanning electron microscope (SEM)?

A
  • Special training is required before use.
  • Samples must be dead as electrons are fired through a vacuum and stains containing heavy elements are used.
  • ‘Artefacts’ can be present in image from staining process.
  • Black and white images only so false colour must be used.
  • Cannot see inside specimens.
  • High cost
  • High energy electron beams can destroy the specimen.
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14
Q

What are the main differences between scanning and transmission electron microscopes?

A
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15
Q

Does light or electons have the shortest wavelength?

A

Electrons

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16
Q

What is cell fracitonation?

A

The process by which cells are broken up and organelles are separated out.

17
Q

Describe the stages of cell fractionation.

A
  1. Tissue is placed in a cold, buffered, isotonic solution.
  2. Tissue and cells are broken up using a homogeniser (blender)
  3. Homogenate is filtered to remove cell debris.
  4. Nuclei in the homogenate are separated by being spun at low speed using a centrifuge (ultracentrifugation)
  5. Supernatent is removed leaving pellet of nuclei.
  6. Supernatent spun at medium speed to create pellet of mitochondrion.
  7. Supernatent removed and spun at high speed to create pellet of ribosomes.
18
Q

Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution cold?

A

To reduce enzyme activity within the cell that could break down organelles.

19
Q

Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution isotonic?

A

If the solution was not of the same water potential as the tissue then organelles could burst as a result of osmotic gain or loss of water.

20
Q

Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution buffered?

A

So that pH is maintained.

A change in pH could affect the enzymes within the cells.

A change in pH could affect the structure of organelles within the cells.

21
Q

What is a homogeniser?

A

A blender used to break up tissues and cells and release organelles.

22
Q

What is a homogenate?

A

The resulting fluid after homogenisation

23
Q

What is a centrifuge?

A

A machine that spins tubes of homogenate at varying speeds (used in cell fractionation)

24
Q

name 2 organelles foundin eukaryotes that cant be seen with a light microscope

A

mitochondria, ribosome, ER, cell surface membrane

25
Q

when preparing a slide for viewing why must you press down hard on the coverslip (without breaking!)

A

To squash tissue (dont push sideways - avoid cells rolling together)

26
Q

why should the specimen be thin?

A

single layer of cells

to allow light to pass through

27
Q

how do you prepare a temporary mount for viewing?

A

add drop of water to slide

take a thin section of tissue - 1 cell thick

place on glass slide (float on water)

add stain

place on coverslip

press down firmly

28
Q

Contrast a TEM and a Optical microcope

A

TEM electrons - light optical

TEM greatER resolution

TEM can see smallER organelles e.g. ribosomes

TEM only dead specimens - light can view dead and live

TEM no colour - optical can

TEM needs thinnER specimen

29
Q

If doing a scientific drawing at an image under the microscope what should you do to ensure the quality of it?

A

dont use shading

use SINGLE lines (no sketching)

add labels/annotations

dont cross label lines

add a magnification/scale bar

30
Q

What type of image does an SEM provide?

A

3D

31
Q

How caould you determine the mean length of a cell using an eye piece graticule?

A

calibrate the graticule using a ruler/stage micrometer

Measure the length of a number of cells (at random) using the graticule

calculate a mean

32
Q

Give some top tips when making a biological drawing

A
  1. continuous lines - no sketching
  2. no shading
  3. draw what you see
  4. add a scale bar or state magnification/scale
  5. Add labels

As-Level Biology (43 decks)

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