Microscopes

Question 1

Why do we use microscopes?

Answer 1

To view cells with an increase in size

Question 2

What is magnification?

Answer 2

The number of times larger than in real life

Question 3

What is the magnification of a light microscope?

Answer 3

X1500

Question 4

Magnification of an electron microscope?

Answer 4

X 1,500,000

Question 5

What is the resolving power?

Answer 5

The ability to distinguish between 2 different objects/points

Question 6

High resolution = what type of wavelength?

Answer 6

Short wavelength

Question 7

What does a high resolution allow us to do?

Answer 7

Allows us to see internal structures and organelles e.g. cell membrane, mitochondria

Question 8

What do all microscopes have?

Answer 8

A source of energy
Lenses for focussing
Sensor

Question 9

What is the wavelength like for an electron microscope (TEM and SEM)?

Answer 9

0.004nm

Question 10

What is the resolution for TEM?

Answer 10

0.1nm

Question 11

What is the resolution for SEM?

Answer 11

20nm

Question 12

What do TEM and SEM use to focus?

Answer 12

Magnets

Question 13

What is the electron micrograph?

Answer 13

The image created on a screen or photographic paper

Question 14

What does the specimen being dehydrated mean? (for a TEM)

Answer 14

The specimen is now dead

Question 15

Why do we cut the specimen into thin slices?

Answer 15

We need the electrons and light to pan through

Question 16

Why do we need to stain the metal ions?

Answer 16

Allows us to see them more easily

Question 17

Does TEM pass through the sample or is it directed onto the sample?

Answer 17

Passes through the sample

Question 18

Does SEM get passed through the sample or directed onto the sample?

Answer 18

Directed onto the sample

Question 19

Is TEM a 2D image or 3D image?

Answer 19

2D image

Question 20

Is SEM 3D or a 2D image?

Answer 20

3D

Question 21

The darker the parts (TEM)?

Answer 21

The thicker the sample

Question 22

Disadvantages of an electron microscope?

Answer 22

Expensive
Have to have specialist training to use them
Dead specimens- have to be dehydrated

Question 23

Iodine?

Answer 23

Stains carbohydrates in plant and animal specimens brown or blue-black
Stains glycogen red

Question 24

Methylene blue?

Answer 24

Stains acidic cell parts (like nucleus) blue. Use on animal, bacteria and blood specimens

Question 25

Eosin Y?

Answer 25

Stains alkaline cell parts (like cytoplasm) pink. Use on plants, animals and blood

Question 26

Toluidine blue?

Answer 26

Stains acidic cell parts (like nucleus) dark blue. Good to show mitosis in plant cells

Question 27

Crystal violet?

Answer 27

Stains bacteria purple

Question 28

Aceto-orcein?

Answer 28

Biological stain for chromosomes and connective tissue

Question 29

Method of illuminating sample in light and TEM and SEM?

Answer 29

Light- light Electron- TEM and SEM

Question 30

Method of focussing waves?

Answer 30

Light- lenses TEM and SEM- magnets

Question 31

Can specimen be living?

Answer 31

Light- yes TEM and SEM- no

Question 32

How is the specimen prepared in light microscope?

Answer 32

Thin specimen on slide with a cover slip

Question 33

How is the specimen prepared in TEM and SEM?

Answer 33

Fixed Dehydrated Stained using metal salts Mounted on a copper grid Placed in a vacuum

Question 34

What types of stains are used and how do they highlight features?

Answer 34

Light- potential staining needed e.g. Acetic orcein TEM and SEM- specimen are stained with metal salts- this causes electrons to scatter differently, giving contrast

Question 35

Advantage of light microscopes?

Answer 35

Cheap

Question 36

Advantage of TEM and SEM?

Answer 36

High magnification and resolution

Question 37

Disadvantages of light microscope?

Answer 37

Low resolution Staining needed for non-coloured specimens

Question 38

Disadvantage of SEM?

Answer 38

Specimen dead Large equipment training needed Vacuum needed Complex staining process Electron may destroy specimen

Question 39

Disadvantage of TEM?

Answer 39

SAME AS SEM But also: specimen must be very thin

Question 40

How does TEM use electrons to generate an image?

Answer 40

sends a beam of electrons through a specimen Measures how many electrons are absorbed by different parts of the specimen thea

Question 41

Is SEM 3D or 2D?

Answer 41

3D

Question 42

Is TEM 3D or 2D?

Answer 42

2D

Question 43

How does TEM give a more detailed image of cell structure than a light microscope?

Answer 43

TEM has greater resolution Electron beams have a shorter wavelength than light

Question 44

Disadvantage of TEM (mark scheme specific)?

Answer 44

Only be used to observe thin sections of specimen Black and white image Dead (dehydrated) specimens Produces artifacts

Question 45

How to prepare a plant cell slide under an optical microscope (mark scheme)?

Answer 45

- place specimen on a slide and use a pipette to put stain on it - use iodine stain - place a cover slip carefully over the top of the sample using tweezers

Question 46

Why can structures like ribosomes and cell membranes not be seen using a light microscope?

Answer 46

Light microscopes do not have high enough resolution and these organelles are too small It is not possible to distinguish between 2 separate points that are close together

Question 47

Explain what an artefact is in microscopy and why it should be minimised.

Answer 47

An artefact is a visible entity that resembles structural detail of the specimen. It should be minimised as it is not a legitimate feature of the specimen

Question 48

4 features which may be found in a prokaryotic cell but not found in a eukaryotic cell?

Answer 48

Capsule Plasmids Flagellum Cell wall

Question 49

Describe the steps required to calibrate the eyepiece graticule of an optical microscope

Answer 49

Use a stage micrometer Insert the eyepiece graticule and line up the scale of the graticule with the scale on the stage micrometer Count the number of subdivisions of the stage micrometer that fit into each division of the eyepiece graticule Multiply that number by the distance between each subdivision of the stage micrometer to give the distance between each division of the eyepiece graticule

Question 50

Explain why an eyepiece graticule needs to be recalibrated when the observer changes to a more powerful objective lens

Answer 50

A change of magnification decreases the width of the field of view As a result, the specimen appear closer but the eyepiece graticule scale does not