microscopy

Question 1

What is the basic function of a microscope? (3)

Answer 1

Instrument which allows you to magnify an object many times;

In order to observe structures / organisms;

Which are impossible to see with a naked eye

Question 2

What are the 3 examples of microscopes? (3)

Answer 2

Optical (light) microscope;

Transmission electron microscope (TEM);

Scanning electron microscope (SEM)

Question 3

What are the benefits of using a stain on your sample? (3)

Answer 3

Increases the contrast of the image;

More internal structures are visible;

Image obtained is much clearer

Question 4

What is differential staining? (3)

Answer 4

When multiple stains are used;

Each stain binds to a specific cell structures or cells;

Common feature of electron microscopes

Question 5

Compare the features of an optical microscope vs an electron microscope (6)

Answer 5

electron: uses beam of electrons
light: uses a beam of light

electron: higher resolution
light: lower resolution

electron: focused using magnets
light: focused using glass lenses

electron: view small structures
light: small structures not visible

electron: specimens are dead
light: specimens can be living

electron: image not in colour
light: image is coloured

Question 6

Why do electron microscopes have a higher resolution than optical microscopes? (1)

Answer 6

Electrons have a shorter wavelength

Question 7

Why is it that optical microscopes generate a coloured image? (1)

Answer 7

Light particles are able to carry information about light, electrons are not able to carry this information

Question 8

What are laser scanning confocal microscopes? (3)

Answer 8

Special type of light microscope;

That uses a laser beam to scan a specimen;

Which will be labelled with a fluorescent tag

Question 9

How does a laser scanning confocal microscope work (in simple terms)? (3)

Answer 9

When the laser beam hits the fluorescent tag;

It gives off light;

Which is focused through a pinhole to a detector

Question 10

What is the function of the eyepiece lens of an optical microscope? (1)

Answer 10

The lens in which the viewer looks through to see the specimen

Question 11

What is the function of the objective lens of an optical microscope? (1)

Answer 11

The lenses that are closest to the specimen for magnification

Question 12

What is the magnification of a low power objective lens? (1)

Answer 12

4x

Question 13

What is the magnification of a medium power objective lens? (1)

Answer 13

10x

Question 14

What is the magnification of a high power objective lens? (1)

Answer 14

40x

Question 15

What is the function of the coarse adjustment knob of an optical microscope? (2)

Answer 15

Brings the specimen into general focus;

By moving the stage up / down

Question 16

What is the function of the fine adjustment knob of an optical microscope? (2)

Answer 16

Tunes the focus;

Increases the detail of the specimen

Question 17

What is the function of the stage clips? (1)

Answer 17

Holds the slide in place

Question 18

What is the function of the stage? (1)

Answer 18

The platform where the slide is placed

Question 19

What is the preparation of a slide using a liquid specimen called? (1)

Answer 19

Wet mount

Question 20

What is the preparation of a slide using a solid specimen called? (1)

Answer 20

Dry mount

Question 21

What is the first step in preparing a slide using a liquid specimen? (2)

Answer 21

Add a few drops of the sample to a slide;

Using a pipette

Question 22

How do you cover the liquid on a slide to prevent air bubbles? (2)

Answer 22

With the coverslip;

Gently pressing down to remove air bubbles

Question 23

What safety precaution should you take when preparing a slide to avoid cross-contamination? (2)

Answer 23

Wear gloves;

Wash hands regularly

Question 24

What is the first step in preparing a microscope slide using a solid specimen? (2)

Answer 24

Use scissors;

To cut a small sample of the tissue

Question 25

Why should you still wear gloves when preparing a slide with a solid specimen? (2)

Answer 25

To prevent stain from dyeing your skin; To protect your hands from sharp objects

Question 26

How do you obtain a thin layer of cells from a solid tissue sample for slide preparation? (3)

Answer 26

Peel away or cut; A very thin layer of cells from the sample; Using a scalpel or forceps

Question 27

Why is it important for the tissue sample to be thin when preparing a microscope slide? (1)

Answer 27

So that light from the microscope can pass through the specimen

Question 28

What should be applied to a tissue sample on a slide before placing the coverslip? (1)

Answer 28

Apply your stain

Question 29

Describe how a transmission electron microscope produces a micrograph (4)

Answer 29

Specimen is stained with electron dense substances e.g. heavy metal salts; Beam of electrons are transmitted through the specimen; Staining substances deflect the electrons in the beam; The pattern that the remaining electrons produce as they pass through specimen is converted into an image

Question 30

Why is the image generated by TEM, an image of the internal features of the specimen only? (1)

Answer 30

Electrons are able to pass through the specimen

Question 31

Describe how a scanning electron microscope produces a micrograph (3)

Answer 31

Specimen is coated with a thin film of heavy metal e.g. gold; Electron beam is scanned to and across the specimen; Electrons that are reflected from the surface are collected and produce an image on a viewing screen

Question 32

Why is the image generated by SEM, an image of the external features of the specimen only? (1)

Answer 32

Electrons are reflected from the specimen

Question 33

Compare the features of a SEM vs TEM (4)

Answer 33

SEM: higher resolution TEM: lower resolution SEM: internal structures only TEM: external structures only SEM: 2D image TEM: 3D image SEM: thin sections only TEM: allows thicker sections

Question 34

What is the difference between 'magnification' and 'resolution'? (2)

Answer 34

Resolution describes how well a microscope can distinguish between two points that are close together; Magnification describes how enlarged an image is compared to the object

Question 35

What is the order of magnification and resolution between the 3 microscopes? (1)

Answer 35

(Highest) TEM > SEM > Optical Microscope (Lowest)

Question 36

How do you calculate magnification of an image? (3)

Answer 36

Image size / Actual size

Question 37

How do you convert measurements from one unit to another? (6)

Answer 37

m - mm (x1000) mm - μm (x1000) μm - nm (x1000) nm - μm (/1000) μm - mm (/1000) mm - m (/1000)

Question 38

What symbol is used for micrometers? (1)

Answer 38

μm

Question 39

What symbol is used for nanometers? (1)

Answer 39

nm

Question 40

What are the rules that must be considered for biological drawings? (5)

Answer 40

Title must be included; Use a sharp pencil for drawings and labels; State the magnification that you are drawing from; No shadings; Annotate all cell components

Question 41

How could you use an eyepiece graticule and stage micrometer to measure the size of a structure? (5)

Answer 41

Place micrometer on stage to calibrate the eyepiece graticule; Line up the scales on the graticule and micrometer; Count how many graticule divisions are in the 100μm on micrometer; Length of 1 eyepiece division - 100μm / number of divisions; Use the calibrated values to calculate the actual length of structures