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ZZZ AS Level Biology > Microscopes > Flashcards

Microscopes Flashcards

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1
Q

what are microscopes?

A

instruments that produce an magnified image of an object

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2
Q

what is magnification?

A

the degree to which an image increases in size from its original image and size

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3
Q

what is resolution?

A

the ability to distinguish between two points

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4
Q

formula for magnification

A

actual size

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5
Q

formula for actual size

A

magnification

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6
Q

to convert millimetre to nanometre …

A

x1000

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7
Q

to convert nanometre to centimetre …

A

/10,000

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8
Q

what is cell fractionation?

A

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

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9
Q

what type of solution is the tissue placed in before fractionation?

A

cold, buffered solution with same water potential

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10
Q

why is the solution cold?

A

to reduce enzyme activity that might break up cells

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11
Q

why is the solution buffered?

A

to prevent changes in pH so that structure/function of enzymes is not altered

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12
Q

why is the solution isotonic?

A

to prevent organelles shrinking/bursting by osmosis

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13
Q

how are the cells broken up?

A

in a homogeniser to release organelles

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14
Q

why is the resultant fluid filtered?

A

to remove debris and complete cells

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15
Q

what happens during ultracentrifugation?

A

organelles in filtered homogenate are separated out in a centrifuge

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16
Q

how does a centrifuge work?

A
  • spins homogenate at low speed for 10 mins - heaviest organelles, nuclei, forced to bottom forming a sediment
  • supernatant removed leaving sediment of nuclei
  • supernatant spun again at faster speed - removes mitochondria
  • process continues increasing speed each time
17
Q

how to prepare a slide

A
  • add drop of water onto slide (temporary mount) using pipette
  • use tweezers to place specimen on top of water drop
  • add drop of stain
  • add coverslip by standing upright next to drop and carefully lowering onto drop without creating air bubbles
18
Q

what are the disadvantages of preparation of specimen for microscopy?

A

due to complex process:

  • artefacts can form (e.g. air bubbles, fingerprints)
  • resolution affected
19
Q

name 5 types of stain

A
  • methylene blue
  • eosin
  • iodine
  • sudan red
  • acetic orcein
20
Q

what is methylene blue used for?

A

makes nuclei more visible

21
Q

what is eosin used for?

A

stains red blood cells and cytoplasmic materials pink

22
Q

what is iodine used for?

A

stains cellulose yellow

23
Q

what is sudan red used for?

A

stains lipids

24
Q

what is acetic orcein used for?

A

stains chromosomes red

25
Q

name two advantages of using electron microscopes

A
  • electrons have shorter wavelength than light so higher resolving power
  • electrons have negative charge so can be focusing using electromagnets.
26
Q

why do electron microscopes have vacuum inside?

A

prevent electrons colliding with air molecules

27
Q

name two types of microscopes

A
  • transmission electron microscope

- scanning electron microscope

28
Q

describe how a transmission electron microscope works

A
  • electron gun fires beam of electrons which are focused by condenser magnet onto specimen
  • specimen absorbs some electrons which makes it dark and lets some electrons pass through making it light
  • 2D image projected onto fluorescent screen producing a photomicrograph
29
Q

describe how a scanning electron microscope works

A
  • electron gun fires beam of electrons which is directed onto surface of specimen
  • beam is passed back and forth across portion of specimen in pattern
  • electrons are scattered and pattern of electrons depends on contour of specimen’s surface
  • 3D image formed by computer analysis of pattern of scattered electrons
30
Q

resolution of TEM

A

0.1 nm

31
Q

resolution of SEM

A

20nm

32
Q

maximum magnification of TEM

A

x 500,000

33
Q

maximum magnification of SEM

A

x 100,000

34
Q

limitations of TEM

A
  • artefacts
  • vacuum
  • thin specimen
  • 2D
  • staining
  • black and white
  • expensive
35
Q

limitations of SEM

A
  • artefacts
  • vacuum
  • staining
  • black and white
  • expensive
  • lower resolution than TEM
36
Q

advantages of light microscopes

A
  • specimen can be alive

- inexpensive

37
Q

limitations of light microscopes

A
  • poor magnification/resolution

ZZZ AS Level Biology (10 decks)

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