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Biology > Microscopy > Flashcards

Microscopy Flashcards

1
Q

What are the three principles of cell theory?

A

1) All living organisms are composed of one or more cells
2) The cell is the basic unit of structure and organisation in organisms
3) Cells arise from pre-existing cells

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2
Q

What did Robert Hooke contribute to cell theory?

A
  • He observed cells in cork
  • Was the first man to use the word ‘cell’
  • Wrote a journal of his micro graphs called micrographia.
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3
Q

What did Antonie van Leeuwenhoek contribute to cell theory?

A
  • First person to document the microscopic observations on LIVE samples
  • Such as bacteria, red blood cells, spermatozoa, muscle fibres
  • Called these microbes ‘tiny animals’
  • Found that living things were indeed made up of cells.
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4
Q

What did Barthélemy Dumortier contribute to cell theory?

A
  • First person to observe cell division in plants using microscopy
  • This was used as evidence for cell theory, that cells were created from old ones, rather than spontaneously created.
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5
Q

What did Theodor Schwann contribute to cell theory?

A

-Proposed the extension of cell theory from just plants to animals as well.

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6
Q

What did Robert Remak contribute to cell theory?

A
  • Discovered that the origin of cells was by the division of pre existing cells
  • Observed cell division occur in frogs eggs immediately after fertilisation.
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7
Q

What did Louis Pasteur contribute to cell theory?

A
  • Had many discoveries in vaccinations, microbial fermentation and pasteurisation.
  • FERMENTATION provided firm evidence against the spontaneous generation of life and cells
  • Allowed full acceptance of full cell theory.
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8
Q

What was Louis Pasteur’s pasteurisation experiment?

A
  • Heated three swan neck flasks
  • One was left open and no bacteria was present
  • Bacteria couldn’t reach fermentable liquid, which went against spontaneous creation
  • One had the long neck removed
  • Bacteria could reach fermentable liquid
  • One was tipped to the side
  • Bacteria could reach fermentable liquid.
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9
Q

What are the disadvantages of electron microscopy?

A
  • Expensive to buy and operate
  • Specimens have to be dead
  • Complex sample preparation
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10
Q

How does a light microscope work?

A
  • Light is focused by glass lenses
  • Light is passed through specimen
  • Light absorbed creates the image
  • Image is magnified by objective lens, then again by eyepiece lens.
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11
Q

What are the advantages of a light microscope?

A
  • Inexpensive to buy and operate
  • Don’t require a lot of training to use
  • Vacuum isn’t required (can use on live samples)
  • Simple sample preparation.
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12
Q

What are the disadvantages of a light microscope?

A
  • Relatively low resolution 200nm

- Relatively low magnification 2000x

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13
Q

What is the equation for magnification?

A

Magnification=Image
_____
Actual

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14
Q

One eyepiece graticule division equation

A

Number of micrometers on the slide micrometer
______________________________________
Number of eyepiece graticule divisions.

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15
Q

How to prepare a dry mount microscope slide?

A
  • Solid specimen viewed whole or cut into thin slices
  • Specimen is place on centre of slide
  • Cover slip placed over specimen
  • Used for pollen, insects, etc.
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16
Q

How to prepare a wet mount slide?

A
  • Specimen is suspended in liquid such as water or immersion oil
  • Cover slip placed over specimen at an angle (avoid air bubbles)
  • Aquatic samples can be viewed this way
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17
Q

How to prepare a squash slide?

A
  • Prepare a wet mount slide
  • Use lens tissue to gently push down on cover slip to squash sample
  • Can also squash sample between to microscope slides as cover slip is delicate
  • This can be used for root tip squashes to observe cell division.
18
Q

How to prepare a smear slide?

A
  • Edge of microscope slide used to smear sample onto another microscope slide
  • This creates a thin, even coating
  • Cover slip is place over sample
  • Used on samples of blood to look at cells.
19
Q

Why must specimens be thin?

A

To allow light to pass through

20
Q

Why must the refractive index of medium used in wet mount be the same as glass?

A

Because this will keep the rays of light straight so an in-focus image is produced.

21
Q

How to focus a microscope?

A
  • Move stage to the highest level using coarse focus mechanism
  • Start with the lowest magnification objective lens
  • Place your microscope slide on stage, held in place by stage clips
  • Move the stage down until it comes into view and focus using the fine focus mechanism.
22
Q

Why do we need to calibrate microscopes?

A

Because the magnification stated on each lens can vary, so we need to calibrate so we can find the true magnification.

23
Q

Why do we stain specimens?

A
  • Higher contrast because different organelles take up more stain than others
  • More internal structure visible
24
Q

What are the rules for a good scientific drawing?

A
  • Drawing and label lines done in sharp pencil
  • Drawing should take up at least half the page
  • Lines need to be continuous
  • Ensure proportions are correct
  • Add labels of what you see
  • Add extra ANNOTATIONS (colour, texture)
  • State magnification
  • Have a title and name stain used
  • Make sure label lines touch what you’re labelling
  • NO shading or colour
25
Q

What are the differences between the eyepiece graticule and stage micrometer?

A
  • Eyepiece graticule remains constant regardless of the magnifications, whereas the stage micrometer increases in size
  • This way, you can calibrate the microscope at every magnification.
26
Q

How does a transmission electron microscope work?

A
  • Beam of electrons, in a vacuum, are transmitted through a sample from an electron gun
  • The beam is focused by electromagnetic lenses
  • Beam passes through specimen and either scatter or hit a fluorescent screen at the base of the microscope, which magnifies the image.
27
Q

How are samples prepared for TEM microscopy?

A

Samples are embedded in resin, stained with heavy metal compounds and cut into into ultra thin sections.

28
Q

How does a scanning electron microscope work?

A
  • A beam of electrons, in a vacuum are focused by electromagnetic lenses
  • The fine beam of electrons scans the surface
  • The secondary electrons emitted by atoms which have interacted with the electron beams are detected using secondary electron detector.
  • These secondary electrons that are collected, create the image.
29
Q

What are the advantages of electron microscopy?

A
  • Much higher resolution
  • Allow a cell’s ultrastructure to be seen
  • Resolving power of TEM 0.5nm
  • Resolving power of SEM 3-10nm
  • Higher magnification over 50,000X
  • TEM produces detailed images of cell ultrastructure
  • SEM produces 3D images and great surface detail of an object inside a cell
30
Q

How are samples prepared for SEM microscopy?

A
  • Have to be small enough to fit on the specimen stage
  • Needs special preparation to increase sample’s electrical conductivity
  • Non-conduction specimens are coated with an ultra thin layer of gold, platinum, chromium, etc.
31
Q

What are artifacts?

A

Anomalies apparent in both microscopy and photography.

32
Q

What is an example of an artefact?

A

Mesosomes

  • People believe they were part of a cell’s ultrastructure but they actually don’t exist
  • They in fact were artefacts
33
Q

What are the disadvantages of electron microscopes?

A
  • Expensive to buy and operate
  • Compex sample preparation
  • Vacuum is required
  • Specimens have to be dead
34
Q

How does a fluorescence microscope work?

A
  • Uses fluorescence to create an image of a specimen
  • Fluorescent dyes contain fluorophores
  • Fluorophores emit longer wavelengths of light
  • This creates a high resolution image
  • The dichroic mirror reflects only one colour of light which passes through the specimen.
35
Q

How does a laser scanning confocal microscope work?

A
  • Is a refinement of the fluorescence microscope
  • Single spot of focused light focused over specimen and causes fluorophores in sample to fluoresce
  • A confocal pinhole blocks any out of focus light, and therefore the image is higher resolution.
36
Q

How does a super resolved fluorescent microscope work?

A

It creates a higher detail image by combining many smaller and overlapping images of a specimen
AND
Digitally superimposing many images on top of each other to create a higher resolution image.
RESOLUTION BREAKS THEORETICAL LIMIT OF 0.2nm for optical microscopes

37
Q

How does an atomic force microscope work?

A

Microscope generates images by scanning a cantilever over the surface of a sample.
Can generate images of things the size of fractions of a nanometer
-1000x more than optical limit
-Shape traced with cantilever is processed and an image is created.

38
Q

What is the definition of magnification?

A

How many times larger the image is than the actual size of the object being viewed

39
Q

What is the definition of resolution?

A

Ability to see individual objects as separate entities

40
Q

How to convert mm to nm?

A

1x10^6

41
Q

How to convert mm to um?

A

1x10^3

Biology (33 decks)

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