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Biology > 2.1 Microscopy > Flashcards

2.1 Microscopy Flashcards

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1
Q

Define resolution

A

The smallest distance between two points that can still be seen as two points.

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2
Q

List all the parts of a light microscope

A

Light source
Eyepiece lens
Objective lens
Coarse focusing wheel
Fine focusing wheel
Stage

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3
Q

What is the maximum magnification for a light microscope?

A

x2000

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4
Q

What is the resolution of a light microscope

A

200nm

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5
Q

What type of images do light microscopes produce?

A

2D

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6
Q

What colour do the images produce from a light microscope?

A

Natural colour/stain

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7
Q

What type of sample can light microscopes use?

A

Living/dead

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8
Q

What is the cost of light microscope?

A

They are good because they are cheap

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9
Q

Name an advantage of light microscopes

A

They are easy to use and are easily portable.

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10
Q

Why are microscopes important in the study of living organisms?

A

Cells are the unit of life
Many organisms are unicellular
Most cells are too small to see without a microscope
Cell components or organelles are even smaller
Idea that need to see organelles to determine function

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11
Q

Why was the cell theory not fully developed before the mid 19th century?

A

Microscopes were too low of a magnification and resolution to see and identify cells

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12
Q

What are the 4 methods of sample preparation?

A

Dry mount
Wet mount
Squash slides
Smear slides

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13
Q

Describe dry mount samples

A

Solid specimen viewed with a cover slip in top, no water needed
Specimen can be viewed whole or cut into thin slices (sectioning)
View small, inanimate objects/living tissue that doesn’t require water to live

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14
Q

Examples of dry mount samples

A

Hair, pollen, dust, insect parts

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15
Q

Describe wet mount samples

A

Specimens suspended in liquid (water/oil)
Cover slips added at an angle
Allows small aquatic organisms to be viewed in this way

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16
Q

Examples of wet mount samples

A

Pond water, cheek cells, blood, sperm samples

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17
Q

Describe squash slide samples

A

A wet mount is prepared first
Pressure then applied to the cover slip to squash the sample, ensuring it is thin enough to transmit the light.

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18
Q

Examples of squash slide samples

A

Observing mitosis in root meristems

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19
Q

Describe smear slide samples

A

Edge of slide is used to smear a sample, creating a thin, even coat on another slide
A cover slip is then added to the sample

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20
Q

Examples of smear slide samples

A

Observing cells within blood

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21
Q

Why do we use staining?

A

Images tend to have low contrast, as most cells do not absorb much light
Stains increase contrast as different cellular components take up stains to different degrees
When contrast is increased, components become more visible

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22
Q

Examples of +ve charged stains

A

Crystal violets, methylene blue

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23
Q

Describe +ve charged stains

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A

Attracted to -ve materials in cellular cytoplasm, staining the components

24
Q

Describe -ve charged stains

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A

repelled by -ve cytosol (aqueous interior of cells)
Dyes stay outside of cells. Cells remain unstained and stand out against the stained background.

25
Examples of -ve charged stains
Nigrosin, congo red
26
What is differential staining?
Distinguish between two types of organism that would otherwise be hard to identify Also differentiates between different organelles of a single organism within a tissue sample
27
Examples of differential staining
Gram stain technique, acid-fast technique
28
Describe gram positive
Thick peptidoglycan layer absorbs surrounding materials, even toxins. Easier to kill, develops resistance slower.
29
Describe gram-negative
Thin peptidoglycan layer covered by multiple thin layers of membrane which eject toxins. Harder to kill, quick to develop resistance
30
What is the acid-fast technique
Distinguishes between mycobacterium (a genus of bacteria) and other bacteria
31
Describe the acid fast technique
1. Lipid solvent is used to carry the carbolfuchsin dye into the cells being studied 2. Cells are then washed with dilute acid-alcohol solution. Mycobacterium are not affected by this and retain the stain which is bright red. 3. Other bacteria lose the stain and are exposed to methylene blue stain, which is blue.
32
How do you get from metres ot millimetres
multiply by 1000
33
How do you get from millimetres to micrometres
x1000
34
How do you get from micrometres to nanometres
x1000
35
How do you get from nanometres to picometre
x1000
36
What is the magnification formula
Magnification = image size/actual size
37
Explain how to do calibration
1. Line up the eyepiece graticule and the stage micrometer 2. Each division of the stage micrometer is 0.1mm long. 3. At a specific magnification 1 division on the stage micrometer is equal to 4,5 divisions on the eyepiece graticule. 4. To work out the size of one eyepiece graticule division you divide the length of one stage micrometer division by the number of eyepiece graticule divisions.
38
What type of microscope has a higher resolution than light microscopes?
Electron microscopes
39
Describe electron microscopes
They use beams of electrons instead of light rays in a light microscope. Electron beams have shorter wavelengths (<1nm) than light, resulting in higher resolution.
40
What are the advantages of electron microscopes?
Up to x500,000 magnification Cell ultrastructure is visible
41
What are the disadvantages of electron microscopes?
Very expensive, can only be used in a high controlled environment Specimens can be damaged by electron beams Complex preparation process... can lead to artefacts.
42
What are the two types of electron microscopes?
Transmission (TEM) Scanning (SEM)
43
Describe TEM microscopes
Beam of electrons transmitted through specimen. Focused to produce an image Similar to light microscopy
44
What is the magnification of TEM microscopes
x1,000,000
45
What is the resolution of TEM microscopes
0.5nm
46
What type of images do TEM microscopes produce
2D
47
What colour do TEM microscope images produce
Black and white
48
What type of sample do TEM microscopes use
Dead
49
Are TEM microscopes expensive?
Yes
50
Are TEM microscopes easy to use
No, they are large and require training and installation
51
Describe SEM microscopes
Beam of electrons sent across surface of specimen. Reflected electrons controlled. Produce 3D images
52
What maginification is SEM microscopes?
x150,000
53
What is the resolution of SEM microscopes?
3-10nm
54
What do TEM and SEM microscopes have in common?
They both produce black and white images They both use dead samples They are both expensive They are both large and require training and installation
55
What is Lase Scanning Confocal Microscopy
Single spot of focused light moved across a specimen, previously marked with fluorescent dye. Fluorescence: absorption and re-radiation of light. Re-radiation (longer wavelength and lower energy) filteered through a pinhole aperture Produces very high resolution images
56
How is LSC applied
Non-invasive- currently used to diagnose eye diseases and in the development of new drugs.

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