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A Level Biology OCR > Magnification > Flashcards

Magnification Flashcards

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1
Q

What do you need to do to see organelles in cells

A

You need to stain the cells

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2
Q

How does a light microscope work

A

An object is placed in a beam of light
The beam passes through a specimen and then through a series of lenses magnifying the image

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3
Q

In order for light to pass through what does the specimen need to be

A

The specimen needs to be thin and transparent

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4
Q

What are the 3 different slide types

A

Dry mount, Wet mount, Squash slides, Smear slides

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5
Q

What is dry mount

A

Dry mount - solid specimens are cut into very thin slices with a sharp blade (sectioning). The specimen is placed in the centre of the slide and a cover slip is placed on top.

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6
Q

What is wet mount

A

Specimens are suspended in a liquid such as water or an immersion oil. It is put on a slide and a cover slip is placed on from an angle.

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7
Q

What is a squash slide

A

A wet mount is prepared, and a lens tissue is used to press down on the cover slip.

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8
Q

What is a smear slide

A

The edge if a slide is used to smear the sample creating a thin even coating on another slide.

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9
Q

What does the eyepiece lens do

A

Magnifies and focuses the image from the objective lens onto the eye

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10
Q

What does the objective lens do

A

Collects light passing through the specimen and produces a magnified image

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11
Q

What is a condenser lens

A

Focuses the light onto the specimen between the cover slip and slide

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12
Q

What is a condenser iris diaphragm

A

Closed slightly to produce a narrow beam of light

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13
Q

What is the typical power of objective lenses

A

4x, 10x, 40x

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14
Q

What is low power

A

The lowest power objective lens

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15
Q

What is low power

A

The lowest power objective lens

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16
Q

Magnification definition

A

A measure of how much the image is enlarged relative to the specimen size

17
Q

Resolution definition

A

the ability to distinguish between 2 points

18
Q

What is maximum resolution

A

1/2 x wavelength

19
Q

What is magnification

A

Size of image/size of object

20
Q

What is an electron microscope

A

Uses a beam of electrons and not light, so has a lower wavelength and higher resolution

21
Q

What is a TEM

A

Stands for a transmission electron microscope

22
Q

What happens in a TEM

A

An electromagnetic coil focuses electrons onto a specimen screen or photographic plate for viewing.

23
Q

What is the resolution and magnification of a light microscope

A

200nm (resolution), x1500-2000

24
Q

What is the resolution and magnification of a TEM

A

0.2-0.5nm, x500,000 - 2,000,000

25
Q

What is a SEM

A

A scanning electron microscope

26
Q

What happens in a scanning electron microscope

A

Electromagnetic coils are used to scan the surface of a specimen with electrons, specimens are coated with gold and silver. Reflected electrons are collected and focused onto a viewing screen or camera.

27
Q

Why must both electron microscopes be done in a vacuum

A

Air particles SCATTER electrons so it must be done in a vacuum. More dense objects scatter more electrons than less dense objects.

28
Q

What is a graticle

A

Is a fixed scale inside an eyepiece. The divisions can be used to measure a magnified image, but you need to calibrate it.

29
Q

What is a stage micrometer

A

It’s a 10mm scale etched into a slide with subdivisions of 0.1mm.

30
Q

How do u use a stage micrometer and graticle

A

We place the stage onto the stage under low power so you can see the graticle and stage micrometer. You then find the number of eyepiece graticle units to stage micrometer units.

31
Q

How do you measure specimens

A

You find the number of units in 1 eyepiece graticle unit and then multiply by the number of eyepiece graticle units in the specimens length or width.

32
Q

What are the advantages of using a light microscope

A

inexpensive to buy and operate
Small and portable
simple sample preparation
Sample preparation doesn’t usually lead to distortion
Vacuum is not required
Natural colour of sample is seen
Specimens can be living or dead

33
Q

What are the benefits of electron microscopes

A

Magnification and resolution

34
Q

What is the resolution and magnification of a SEM

A

3-10nm and x100,000 - 500,000

A Level Biology OCR (3 decks)

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