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y - Biology - CAP 5 > 2. Light and Electron Microscopes > Flashcards

2. Light and Electron Microscopes Flashcards

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1
Q

Whatyou 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 transmissionelectron 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 advantagesof 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

2µm

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 fractionation?

A

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

17
Q

Describe the stages of cell fractionation.

A
  • Tissue is placed in a cold, buffered, isotonic solution.
  • Tissue and cells are broken up using a homogeniser (blender)
  • Homogenate is filtered to remove cell debris.
  • Nuclei inthe homogenate are separated by being spun at lowspeed using a centrifuge (ultracentrifugation)
  • Supernatent is removed leaving pellet of nuclei.
  • Supernatent spun at medium speed to create pellet of mitochondrion.
  • 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 ensurethe 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

y - Biology - CAP 5 (80 decks)

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