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Biology A level > Cell structure- Microscopy > Flashcards

Cell structure- Microscopy Flashcards

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1
Q

What does a microscope do?

A

Image is enlarged by the product of the eye piece lens magnification, and the objective lens magnification

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2
Q

What’s magnification?

A

The amount of times the image is larger than the object

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3
Q

Function of the eye piece lens?

A

Too look through and it magnifies

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4
Q

Function of the nose piece?

A

Changing objective lens

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5
Q

Function of the fine focus adjuster?

A

Make small adjustments to focus

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6
Q

Function of the Dimmer?

A

Changes the amount light shone on the slide

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7
Q

Function of the course focus adjuster?

A

Make larger adjustments to the focus

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8
Q

Function of the low power objective lens?

A

Magnifies the object even further, can be changed for different amounts of zoom

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9
Q

Function of the light?

A

So the object can be viewed

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10
Q

What does SEM stand for?

A

Scanning electron microscope

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11
Q

What does TEM stand for?

A

Transmission electron microscope

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12
Q

How does an electron microscope work?

A

Beam of electrons with wavelength less than 1 nm used, is used to illuminate the specimen.
Has to pass through a vacuum, to ensure electrons travel in a straight line, this means specimen must be dead

Electrons focused on to fluorescent screen or photographic plate, which produces a “greyscale” image. These area called electron micrographs and have colour added to them digitally
Magnifications x500,000

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13
Q

Why do electron beams give higher resolution?

A

Smaller wavelength so they pass through object more so more objects can be seen separate and distinguished between each other

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14
Q

Features of a SEM?

A

Prep is spraying heaving metals onto specimen
Beam of primary electrons sent across surface of a specimen using electromagnetic lenses
Secondary electrons emitted from the surface are collected
Resolution isn’t as good as TEM, but produces 3D images
x100,000- x 500,000 magnification
Resolution is 3-10nm

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15
Q

Features of a TEM?

A

Heavy metal salts are used for staining, as they provide contrast in where the salts have been collected and where they haven’t, as electrons can pass through areas where the salts aren’t present but can’t where they are
Electrons are transmitted through the specimen and focused using an electromagnetic lens
High resolution 0.2-0.5nm
x500,000- x2,000,000 magnification

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16
Q

Features of a laser scanning confocal microscope?

A

Light microscope
Uses laser beams (higher intensity so more illumination), focused through a lens onto the specimen, causing it to give off fluorescent light
This light is then focused through a pinhole to give an image
Pinhole blocks out any unfocused light, making it clearer than normal
3D image can be produced by creating images at different focal planes
Specimen stained with fluorescent dyes
resolution > 200nm

17
Q

Benefits of light microscope?

A 
Cheap
Specimen dead or alive
Portable
simple slide prep
Already coloured image
18
Q

Negatives of light microscope?

A

Poor maximum magnification (1,500-2,000) due to poor resolution, due to light having longer wavelengths
Only 2D image made
poor resolution 200nm

19
Q

Benefits of electron microscopes?

A

High magnification due to high resolution

3D image can be produced

20
Q

Negatives of electron microscope?

A

Expensive
Specimen has to be dead
Not portable
Complex slide prep, can lead to artefacts

21
Q

What’s resolution?

A

The shortest distance between 2 objects which can still be distinguished by the viewer

22
Q

What are the rules for a biological drawing?

A

Drawing fills at least half of space provided
Sharp HB pencil used
Single unbroken lines
No shading or colouring
Label lines point to features, and have no arrow heads
Annotations in pencil
Scale line

23
Q

Formula for magnification?

A

Magnification= Image size/ actual size of image

24
Q

How to use the magnification formula?

A

Measure the length of image size you are trying to find
Read what it’s actual length is
Convert them into the same units
Then divide the Image size by the actual size of the image

25
Q

Symbol and value of millimetres?

A

mm, = 1m x 10 to the power of -3

26
Q

Micrometre symbol and value?

A

µm= 1m x 10 to the power of -6

27
Q

Nanometre symbol and value?

A

Nm = 1m x 10 to the power of -9

28
Q

Why is staining useful in light microscopy?

A

It can be used to better visualise cells, and specific cell components, by giving them colour, as some biological material isn’t coloured

29
Q

In light microscopy what does staining need to do?

A

Reveal new features, via a chemical reaction

30
Q

What molecule does iodine bond to?

A

Starch, making it blue/black

31
Q

What molecule does carmine bond to?

A

Glycogen staining it red

32
Q

How to use a light microscope?

A

make sure the objective lens is 4X, and the stage is high as possible
Place slide onto stage
focus the image using the focus adjusters, only moving downwards, and the dimmer
Repeat on 10X , and 40x optical lenses

33
Q

How to produce a temporary wet mount of living tissue

A

Wet mount is when the specimen is suspended in water, temporary as water evaporates
Use water from it’s natural environment to prevent damaging the specimen via osmosis
Put small drop of water in centre of microscope slide
Put specimen in water
Put cover slide on top, carefully to avoid air bubbles

34
Q

Why do specimens need to be thin?

A

To allow light to travel through them to the optical lens

35
Q

Why might a tissue be misleading due to the very thin nature of the slice?

A

Your only getting a very small sample space of a specific area, so cells may be missing as they aren’t located in that specific area

36
Q

How might adjusting the plane of focus alter what you see within a cell?

A

Cells are 3D, so when altering the focus certain layers of the cell will come in and out of focus, so only certain bits can be viewed at a time

37
Q

What’s an eye piece graticule?

A

An eye piece lense with a scale on it

38
Q

How to use an eye piece graticule and a stage micrometre to measure cells?

A

Put the eye piece graticule in
Focus on the stage micrometre
For each objective lens calibrate the graticule, by finding the value of one eye piece unit in nanometres, using the stage micrometre
Then focus on the cell your looking at and use the eye piece units to calculate the cells length in micrometres

Biology A level (19 decks)

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