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A Level Biology > Microscopes > Flashcards

Microscopes Flashcards

1
Q

Define magnification?

A

The degree to which the size of an image is larger than the object itself

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2
Q

Define resolution?

A

The minimum distance apart that two objects can be in order for them to appear as two separate items

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3
Q

What is used to measure the size of cells (in a microscope)?

A

Eyepiece graticule

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4
Q

What scale are cells/objects measured by using a microscope?

A

Eye piece units (epu)

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5
Q

What are the rules when completing a biological drawing?

A
  • Use a sharp pencil
  • Should take up at least half a page
  • Line need to be clear and continuous (no shading/sketching/colouring)
  • Ensure proportions are correct
  • Label all features you have shown
  • Rule label lines
  • Don’t cross label lines or use arrows
  • Don’t write on label lines
  • Ensure label lines touch the part you are labelling
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6
Q

What is the equation for magnification?

A

IAM
Image size/actual size

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7
Q

Describe how you could make a temporary mount of a piece if plan tissue to observe the position of starch granules?

A
  • Add a drop of water to the glass slide
  • Obtain a THIN section of plant tissue (potato) to ensure light can pass through
  • Stain with iodine in potassium iodide solution
  • Lower cover slip on slide using a mounted needle (ensures no air bubbles)
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8
Q

How do you calibrate a microscope to work out the mean diameter of starch grains?

A
  • Measure the diameter of the grain using the eye piece graticule
  • Calibrate the eye piece graticule using a stage micrometer at the same magnification
  • Randomly sample 10+ grains and calculate the mean
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9
Q

What is cell fractionation?

A

The process in which cells are broken up (lysis) and different organelles within the cell are separated out so they can be studied in detail

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10
Q

Before cell fractionation can begin what type of solution must the tissue be placed in?

A

A cold, buffered, isotonic (same water potential) solution

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11
Q

What does isotonic mean?

A

The solutions have the same water potential

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12
Q

Why should the solution be cold?

A

To reduce enzyme activity to prevent organelles being broken down (by digestion)

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13
Q

Why should the solution be buffered?

A

So the pH doesn’t fluctuate so proteins don’t denature

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14
Q

Why should the solution be isotonic (have the same water potential)?

A

To prevent organelles shrinking or bursting as a result of osmotic gain/loss of water

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15
Q

Describe the process of cell fractionation?

A
  • Homogenisation- break open cells by vibrating or grinding them up (in a homogeniser - blender) to release organelles from cells
  • Filtration - the resultant fluid (homogenate) is filtered to remove any debris (whole cells/bits of tissue’)
  • Ultracentrifugation - the fragments in the filtered homogenate are separated in a centrifuge at increasing speeds
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16
Q

Describe the process of ultracentrifugation?

A
  • The first centrifuge spin is low-speed and separates the heaviest organelles (nuclei) out first. They are forced to the bottom of the tube where a thin sediment/pellet forms whilst the less dense remain in suspension above (supernatant)
  • The supernatant ( is removed leaving just the sediment) is then transferred to the next tube and spun at a faster speed ( this next pellet contains the next most heavy/dense organelle -mitochondria)
17
Q

What are the three types of microscopes?

A
  • Light/Optical
  • Transmission Electron Microscope (TEMs)
  • Scanning Electron Microscopes (SEMs)
18
Q

What type of electromagnetic radiation do optical microscopes use?

A

Beams of visible light (has a long wavelength which reduces resolving power)

19
Q

What type of electomagnetic radiation do TEMs and SEMs use?

A

Beams of high energy electrons (which have a shorter wavelength leading to a higher resolving power)

20
Q

Compare the size of magnification between optical microscopes and TEMs/SEMs?

A

Optical microscopes have a lower magnification (x400)
SEMs and TEMs have a higher magnification (x 1,000,000)

21
Q

Which microscope has the highest resolving power ?

A

TEMs

22
Q

Compare the resolving power for all three microscopes?

A
  • Optical = lowest (0.2 ųm)
  • SEMs = Higher (5 - 20 nm)
  • TEMs = Highest (0.2 nm)
23
Q

Which is the only microscope to produce a 3D image?

A

SEMs
Scanning Electron Microscope

24
Q

How do you do focus an optical microscopes?

A

Use pairs of lenses

25
Q

How do you do focus an electron microscopes

A

Use electromagnets

26
Q

Which microscope enables you to view a specimen in colour?

A

Optical microscope
The TEMs and SEMs only view specimens in black and white

27
Q

Which microscope can view live specimens?

A

Optical microscope
The electron microscopes take place in a vacuum so only dead/dehydrated specimens can be viewed

28
Q

Which microscope require a thin specimen?

A

Light/optical microscopes and TEMs
SEMs can view thicker specimens as they produce a 3D image

29
Q

Which is the only portable microscope?

A

Optical microscopes

30
Q

Compare the value of microscopes?

A
  • Optical microscopes are cheap
  • Electron microscopes are expensive
31
Q

Which microscope requires the most complex staining process?

A

TEMs (transmission electron microscopes)
- requires use of heavy metals

SEMs and optical microscopes don’t need staining

32
Q

What is an artefact?

A

Something you see under a microscope (when looking at a prepared sample) that isn’t actually part of the specimen (eg, dust and bubbles, fingerprints)

33
Q

Which microscope suffers mostly from presence of artefacts?

A

TEMs due to more complex staining process

34
Q

What are examples of artefacts?

A

Dust
Bubbles
Fingerprints

35
Q

What stain is used to make the cytoplasm show up?

A

Eosin

A Level Biology (15 decks)

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