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BIOLOGY 2.1.1 cell structure > microscopy > Flashcards

microscopy Flashcards

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1
Q

describe how light microscopes work

A

uses light rays and a number of different lenses to produce an image viewed at the eyepiece

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2
Q

what are the two different types of microscopes

A

light microscopes
electron microscopes

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3
Q

what is the maximum resolution and magnification of a light microscope

A

resolution - 50-200nm
magnification - x1500

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4
Q

what are the two types of electron microscopes

A

transmission electron microscopes (TEMs)
scanning electron microscopes (SEMs)
laser scanning confocal microscope

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5
Q

describe how a transmission electron microscope work

A

an electron beam is directed at the sample with the electrons passing through less dense parts producing a contrasted 2D image

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6
Q

describe how a scanning electron microscope works

A

an electron beam is directed at the sample and reflected electrons are collected producing a 3D image of the cell surface
uses electro magnets

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7
Q

describe how a laser scanning confocal microscope work

A

specimen is treated with dye that is taken up by the cell components at different extents, a laser beam scans the specimen making the dye fluorescent and the emitted light is passed through a pinhole producing an image
a 3D image is produced and depth of image can be seen

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8
Q

image produced by a laser scanning confocal microscope

A

3D image with depth

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9
Q

pros of a light microscope

A

can observe living things
does not use harsh chemicals
easy to set up and use
inexpensive
can observe whole cells and tissues

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10
Q

cons of light microscopes

A

low magnification
low resolution - cant see organelles apart from the nucleus
cant observe Golgi, mitochondria, SER, RER

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11
Q

pros transmission microscopes

A

high magnification
high resolution
can see details inside the cells e.g. organelles
2D

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12
Q

cons of transmission microscopes

A

can only see dead material as materials must be put in a vacuum (all air molecules have been removed) because these will deflect the beams of electrons
samples must be stained with metals. these harsh chemicals used in preparation can cause artefacts
expensive

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13
Q

pros of scanning microscope

A

high magnification
high resolution
can see details of the surfaces of structures shown in 3D

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14
Q

cons of laser scanning microscopes

A

can only see dead material as materials must be put in a vacuum (all air molecules have been removed) because these will deflect the beams of electrons
samples must be stained with metals. these harsh chemicals used in preparation can cause artefacts
expensive

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15
Q

pros of laser scanning confocal microscopes

A

can see living cells
can observe cell processes by tracking molecules
flurescent tag
higher resolution than light microscope
depth of image can be seen
produces a 3D image

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16
Q

cons of a laser scanning confocal

A

more expensive than light microscope
more complex than light microscope

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17
Q

magnification and resolution of TEM

A

magnification: x500,000
resolution: 0.05 - 1nm

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18
Q

magnification and resolution of SEM

A

magnification: x500,000
resolution: 5-50 nm

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19
Q

define magnification

A

the number of times larger an image is than the actual object

20
Q

resolution

A

the ability to distinguish separate points on an image as two separate object

21
Q

magnification eq

A

magnification = image size / actual size

22
Q

making an oinion cell slide

A
  1. carefully use a shape blade to peel a thin layer from the oinion so light can penetrate through and will enable a view of indibidual cells. Wear gloves to ensure there is no cross-contamination of foreign cells
  2. Gently place the sample onto the slide (using a wet mount) to prevent dehydration. (Wet mounts are used for mobile specimens/living tissues).
  3. stain the sample with a drop of iodine this will ensure you can seen and distinguish the internal parts of the cell more clearly/use more than more one stain to improve contrasts - place stain at edge of sample (no the centre) use blotting paper to remove excess stain - place stain on one stain
  4. gently lower a coverslip at a 45 degree angle to cover the smple to spread the cells. place at an angle to push any to the slide and reduce aur bubbles
23
Q

what are the four slide preparation methods

A

dry mount
wet mount
squash slides
smear slides

24
Q

dry mount

A

specimen is placed in the centre of the slide with cover slip

25
Q

examples of dry mount

A

hair
pollen
dust
muscle or plant tissue

26
Q

wet mount

A

specimen in suspended in a liquid such as water or immersion oil and a cover slip is placed from an angle

27
Q

examples of wet mount

A

aquatic species

28
Q

squash slides

A

wet mount is prepared first and a lens tissue is used to gently press the cover slip

29
Q

examples of squash slides

A

root tips to observe cell division

30
Q

examples of squash slides

A

root tips to observe cell division

31
Q

smear slides

A

the edge of a slide is smeared with the sample, creating a thin and even smear with a cover slip over

32
Q

examples of smear slides

A

blood cells

33
Q

purpose of staining

A

to increase the contrast between different components making them more visible and identifiable

34
Q

staining has to be….

A

air-dried before being heat-fixed by passing through a flame

35
Q

methylene blue stain

A

staining living tissue - dark blue nucleus
light blue cytoplasm and bacteria cells

36
Q

iodine solution stain

A

staining living plant cells
dark blue/black starch gains

37
Q

acidified phloroglucinola

A

staining lignin red in the xylem walls

38
Q

acetic orcein stain

A

stains nuclei and chromosomes red

39
Q

eosin stain

A

stains (dead) cytoplasm and some organelles red

40
Q

light green stain

A

stains plant cell walls green

41
Q

preparing transmission electron microscope specimens

A

specimen needs to absorb electrons so it is treated with dye, heavy metal compounds are also used

42
Q

why is a drop of water added when preparing a temporary mount

A

preparing cells being damaged by dehydration

43
Q

why is an image unclear under a light microscope

A

use coarse focus for clearer image
specimen not thin enough for light to pass through
cross contamination with foreign cells

44
Q

why are heavy metal compounds used as dye

A

absorb electrons well

45
Q

method of making a blood smear

A
  1. pipette blood sample onto one side of microscope slide
  2. add fixant to make liquids not run off and add stain if you want to see a specific part of each cell
  3. add cover slip to spread the blood smear across the slide
  4. the cover slip must be added at an angle to prevent air bubbles
  5. leave to air dry
46
Q

how to use a light microscope + calibration

A
  1. clip the slide onto the stage
  2. select the lowest powered object lens
  3. use the corse focus nob to move the objective lens to just above the slide
  4. look down the eyepiece and adjust the focus with the fine adjustment knob, until a clear image appears
  5. if a higher magnification is needed, swap to a higher powered objective lens and refocus - re-calibrate
    to find the size of specimen:
  6. fit an eyepiece graticule to the eyepiece
  7. place a stage micrometer (microscope slide with an accurate scale) on the stage - this will aid accuracy
  8. calibrate - identify the length in um of 1 epg
  9. measure the length of the specimen in epg
47
Q

Explain how to measure the diameter of the nucleus of one of the white blood cells, when observing the cells through a light microscope. EQ

A
  1. use eyepiece graticules
  2. calibrate graticule using stage micrometer
  3. measure the diameter of the nucleus in graticules
  4. take repeated measurements and calculate a mean diameter
  5. use calibrate epg to calculate diameter

BIOLOGY 2.1.1 cell structure (4 decks)

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