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OCR A-LEVEL Biology > Module 2 Section 1 - Microscopy > Flashcards

Module 2 Section 1 - Microscopy Flashcards

1
Q

what is magnification

A

how much bigger the image is than the specimen (the sample your looking at)

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2
Q

what do microscopes produce

A

a magnified image

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3
Q

how is magnification calculated

A

magnification = image size / object size

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4
Q

what is resoultion

A

how well a microscope distinguishes between two separate points that are close together

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5
Q

if a microscope cant separate two separate objects then….

A

increasing the magnification wont help

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6
Q

what is the formula triangle which has image size, magnification and obejct size

A

image size
magnification x object size

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7
Q

what are three microscopes we need to know

A

-light microscopes
-laser scanning confocal microscopes
-electron microscopes

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8
Q

what does a light microscope use to form images

A

light

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9
Q

what is said about the resolution of light microscopes

A

lower than electron microscopes

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10
Q

what are light microscopes usually used for

A

whole cells or tissues

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11
Q

what is typically the maximum useful magnification of light microscopes

A

x1500

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12
Q

what do laser scanning microscopes use to from images

A

laser beams (usually tagged with fluorescent dye)

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13
Q

what does thee laser do the dye

A

gives off light - light is then focused through a pinhole onto a detector

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14
Q

what happens after light is focused on the detector

A

detector hooked up to a computer which generates an image - image can be 3D

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15
Q

what does the pinhole mean

A

any out of focus light is blocked meaning microscope produces a much clearer image

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16
Q

what can these microscopes also be for?

A

looking at different depths in thick specimens

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17
Q

what do electron microscopes use to form images

A

electrons

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18
Q

what two kinds of electron microscopes are there

A

-transmission electron microscope (TEM)
-Scanning electron microscope (SEM)

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19
Q

what do transmission electron microscopes use to form images

A

electromagnets to focus a beam of electrons which is transmitted through the specimen

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20
Q

why do some parts f TEM image look darker than others

A

because they are denser

21
Q

why are TEMs good

A

they provide high resolution images

22
Q

Why are TEMs not so good

A

Can only be used on thin specimens

23
Q

How do SEMs form images

A

They scan a beams of electrons across a specimen which knocks off electrons from the specimen gathered in a cathode ray tube to form an image

24
Q

Why are SEMs good

A

Shows the surface of the specimen and can be 3D

25
Q

What is the maximum resolution of a light microscope

A

0.2 micrometers

26
Q

What is the maximum resolution of TEMs

A

0.0002 micrometers

27
Q

What is the maximum resolution of SEMs

A

0.002 micrometers

28
Q

What is the maximum magnification of light microscopes

A

x 1500

29
Q

What the maximum magnification of TEMs

A

Can be more than x1 000 000

30
Q

What is the maximum magnification of SEMs

A

Usually less than x 500 000

31
Q

Why do you need to stain samples

A

Objects being viewed may be transparent so you stain the sample so components of the cell can be viewed

32
Q

What type of staining is used for light microscopes

A

Some sort of dye

33
Q

Different stains …..

A

Are used to make different things show up. More than one stain can be used at once

34
Q

What type of staining is used for electron microscopes

A

Objects are dipped in a solution of heavy metals

35
Q

Why are sample for electron microscopes dipped in heavy metals

A

The metal ions scatter the electrons, again creating contrast

36
Q

What do you need to view a specimen under a light microscope

A

A microscope slide

37
Q

What are the different types of slides

A

Dry Mount
Wet Mount

38
Q

What is a dry mount

A

A specimen that is placed on a slide with or without a coverslip over it.

39
Q

What is wet mount

A

A specimen is placed on a drop of water on the slide, with a coverslip placed over it

40
Q

What is the first stage of using a microscope

A

-Clip the slide on the stage

41
Q

What is the second stage of using a microscope

A

Select the lowest powered objective lens

42
Q

What is the third stage of using a light microscope

A

Use the coarse adjustment knob to bring the stage just below the objective lens

43
Q

What is the fourth stage of using a light microscope

A

Look down the eyepiece, use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

44
Q

What is the fifth stage of using a light microscope

A

Adjust the fine adjustment knob to focus until a clear image shows

45
Q

What is the sixth stage of using a light microscope

A

You can see the specimens under a greater magnification by swapping to a higher powered objective lens and refocus

46
Q

What is the eyepiece graticule used for

A

Finding the size of the specimen

47
Q

Where is the eyepiece graticule fitted

A

Onto the eyepiece

48
Q

What is a stage micrometer used for

A

Used to work out the value of the divisions of the eyepiece graticule at a particular magnification

49
Q

Why is the eyepiece graticule described as a transparent ruler

A

It is like a ruler but with no units or numbers

OCR A-LEVEL Biology (48 decks)

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