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A-level biology > microscopy > Flashcards

microscopy Flashcards

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1
Q

define magnification

A

how much bigger the image is compared with the actual size of the object

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2
Q

what is the equation to calculate magnification

A

image size/ actual size

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3
Q

how many mm in a m

A

1m=1000m

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4
Q

how many um in a mm

A

1mm=1000um

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5
Q

how many um in a m

A

1m= 1000000um

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6
Q

how many um in a nm

A

1um=1000nm

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7
Q

define resolution

A

the smallest distance two points can be separated and still be seen as separate items

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8
Q

(exam q) why do we use ‘this’ unit

A
  • it is the most appropriate unit
  • avoids the use of excessive decimal places
  • avoids the use of using unnecessary standard form
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9
Q

to what limit can the human eye can see

A

+- 0.25mm

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10
Q

what are the features of the light microscope (4)

A
  • limited to a resolution of 0.4um
  • can use living specimens
  • easy to prepare specimen
  • images produced in colour
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11
Q

what are the features of the electron microscope (6)

A
  • has a resolution up to 0.1nm
  • specimen must be dry, dead and extremely thin
  • extremely complex preparation of the specimen
  • images produced in black and white
  • slicing the sample to make it thin can damage the inter-molecular structures
  • image can produce artifacts (things on the object that arent actually real) e.g. air bubbles
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12
Q

describe the resolving power of the transmission electron microscope

A

it has a maximum resolution of 0.1nm which is not always achieved due to the difficult specimen preparation and the high energy (electron) beam which can destroy the specimen

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13
Q

advantages of the light microscope (3)

A
  • can see living specimens
  • easy to prepare specimen
  • variety of coloured stains
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14
Q

disadvantages of the light microscope

A
  • low resolution so organelle details/smaller components are not visible
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15
Q

advantages of the transmission electron microscope (2)

A
  • has a very high resolution at high magnification
  • can identify detailed organelle/sub-organelle structure
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16
Q

disadvantages of the transmission electron microscope (4)

A
  • specimen not alive (in a vacuum)
  • difficult preparation (very thin specimen, complex staining)
  • produces a black and white image
  • artefacts can spoil image
17
Q

to what resolution can the scanning electron microscope reach to

A

20nm

18
Q

advantages of the scanning electron microscope (1)

A
  • 3D images show structural formation
19
Q

disadvantages of the scanning electron microscope (3)

A
  • specimens are not alive
  • difficult to prepare specimen
  • produces a black and white image
20
Q

why do we stain specimens

A

it helps to identify specific features of cells and improves contrast within the specimen

21
Q

name the three processes to fractionate a cell (isolating and separating individual components)

A

1- homgenisation
2- filtration
3- differential ultracentrifugation

22
Q

describe the process of homogenisation

A

cells vibrated or grinded in a blender, breaking them open.

23
Q

why is a cold isotonic buffer used in homogenisation

A

-cold to stop organelle activity (hydrolytic enzymes in lysosomes)
-> lysosomes used to digest material inside the cell. contain hydrolytic enzymes which hydrolyses the components in the homogenate (biological molecules) such as polypeptides
- isotonic to prevent the movement of water in and out of the cell through osmosis (prevents organelles bursting through the movement of water in)

24
Q

why is a buffer solution used in homogenisation

A

it prevents change in PH levels, stopping important proteins from being denatured

25
Q

describe filtration

A

solution is filtered through a gauze to remove cellular debris

26
Q

describe differential ultracentrifugation

A
  • solution spun in a centrifuge at a low speed
  • heaviest organelles fall to the bottom (form a pellet), other organelles stay suspend in the fluid above the pellet (called the supernatant)
  • pellet removed or supernatant depending on what you are looking for-
  • (pellet removed) supernataant spun at a higher speed
  • pellet forms. supernatant removed (these contain the lightest organelles)

A-level biology (30 decks)

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