Microscopy

Question 1

What are the two lenses of a compound light microscope?

Answer 1

The objective and eyepiece lens

Question 2

Where is the objective lens positioned?

Answer 2

Near the specimen

Question 3

Where is the eyepiece lens positioned?

Answer 3

Near your eye

Question 4

How do the objective and eyepiece lens work together and what does this allow for?

Answer 4

The objective lens produces a magnified image, which is magnified again by the eyepiece lens. This allows for much higher magnification and reduced chromatic aberration

Question 5

What is the process of slicing very thin slices of a specimen known as?

Answer 5

Sectioning

Question 6

Why are stains used on specimens in light microscopy?

Answer 6

Stains increase contrast as different components within a cell take up stains to different degrees. The increase in contrast allows components to be more visible and more easily identified.

Question 7

What is differential staining?

Answer 7

Can distinguish between two types of organism

Question 8

Give 2 differential staining techniques

Answer 8

Gram stain and acid-fast technique

Question 9

What is the formula for magnification?

Answer 9

Magnification = Size of image / Actual size of object

Question 10

What are transmission electron microscopes (TEMs)?

Answer 10

Where a beam of electrons is transmitted through a specimen and focussed to produce an image

Question 11

What are scanning electron microscopes (SEMs)?

Answer 11

Where a beam of electrons are sent across the surface of a specimen and the reflected electrons are collected to produce the image

Question 12

What is the resolving power of TEMs?

Answer 12

0.5nm

Question 13

What is the resolving power of SEMs?

Answer 13

3-10nm

Question 14

What type of image will SEMs give?

Answer 14

3D

Question 15

In electron microscopes, what do the specimens have to be?

Answer 15

Dead

Question 16

3 difference between light and electron microscopes

Answer 16

In electron a vacuum is required, black and white images are produced and specimens must be dead, whereas in light a vacuum is not required, the natural colour or staining of specimen is seen and specimens can be living or dead

Question 17

3 pros of light microscopes

Answer 17

Inexpensive
Small and portable
Simple sample preparation

Question 18

What is the resolving power of light microscopes?

Answer 18

200nm

Question 19

What is the magnification of light microscopes?

Answer 19

Up to x2000

Question 20

What is the magnification of electron microscopes?

Answer 20

Over x500,000

Question 21

How do laser scanning confocal microscopes work?

Answer 21

It moves a single spot of focused light across a specimen (point illumination). This causes fluorescence, which is sent back up through a pinhole opening and detected by the detector

Question 22

What happens to the out of focus light and what does this mean for the resolution in confocal microscopy?

Answer 22

The out of focus light is blocked and does not pass through the pinhole, and so is not detected. This light from other parts of the specimen would reduce resolution and cause blurring, however this is prevented

Question 23

What is the definition of resolution?

Answer 23

The shortest distance between two points that can be distinguished

Question 24

Why are we able to see with a greater resolution with electron microscopes compared to light microscopes?

Answer 24

Electron microscopes use electrons instead of light and electrons have a shorter wavelength than light, which produces images with a higher resolution

Question 25

What is the definition of magnification?

Answer 25

Magnification is how much bigger the image is compared to the original object viewed with the naked eye