2.1.1- Microscopes

Question 1

Define the term ‘magnification’.

Answer 1

The number of times larger an image appears, compared to the size of the original object.

Question 2

Define the term ‘organelles’.

Answer 2

Small structures that are within cells- each of which has a specific function.

Question 3

Define ‘photomicrograph’.

Answer 3

Photograph of an image seen using an optical microscope.

Question 4

What is ‘resolution’?

Answer 4

The ability to be able to distinguish between two points clearly.

Question 5

Microscopes produce what kind of magnification?

Answer 5

Linear magnification.

Question 6

List four reasons as to why optical (aka light) microscopes are still used in schools, colleges and labs.

Answer 6

• relatively cheap
• relatively easy to use
• can be used to study WHOLE AND LIVING SPECIMENS
• portable- can be used in the field and lab

Question 7

Explain simply how optical microscopes work.

Answer 7

They rely on lenses to focus a beam of light.

Question 8

What is the maximum magnification of an optical microscope?

Answer 8

X1500

Question 9

Explain why light microscopes can not magnify any higher than around x1500 effectively.

Answer 9

As their resolution is limited- they cannot magnify any higher whilst also producing clear images.

Question 10

What is the maximum resolution of optical microscopes?

Answer 10

200 nanometers.

Question 11

What are the four types of microscopes?

Answer 11

• Optical microscope
• Laser scanning microscope
• Scanning electron microscope
• Transmission electron microscope

Question 12

Explain why ribosomes cannot be seen using an optical microscope.

Answer 12

They are about 20nm diameter so are smaller than the resolution of the optical microscope (200nm)

Question 13

What is the formula for calculating the total magnifying power of an optical microscope?

Answer 13

Total magnification= objective lens magnifying power ‘X’ magnifying power of eyepiece lens

Question 14

Define the term ‘electron micrograph’.

Answer 14

Photograph of an image that is seen using an electron microscope.

Question 15

How do modern digital microscopes display their image?

Answer 15

On computer screen.

Question 16

What is the alternative name for laser scanning microscopes?

Answer 16

Confocal microscopes.

Question 17

Explain how laser scanning microscopes work.

Answer 17

They use laser light to scan an object point by point and assemble the pixel information by computer, on a computer screen.

Question 18

The images produced by laser scanning microscopes are high _________ and show high __________.

Answer 18

High resolution.

High contrast.

Question 19

Laser scanning microscopes have a special feature. What is that?

Answer 19

Depth selectivity.

Question 20

Explain what depth selectivity is- a feature of laser scanning microscopes.

Answer 20

It means they can focus on structures at different depths within a specimen. It makes it useful to observe full and living specimens, as well as cells.

Question 21

What are the two main places where laser scanning microscopes are used?

Answer 21

The medical profession and biological research.

Question 22

Describe an example of how laser scanning microscopes are used in the medical profession.

Answer 22

They’re used to observe fungal filaments in the cornea of the eye of a patient with a fungal corneal infection. This gives a swift diagnosis- therefore, giving a more effective treatment.

Question 23

What are the two different types of electron microscopes.

Answer 23

• Transmission electron microscopes.

* Scanning electron microscopes.

Question 24

What is the maximum resolution of a laser scanning microscope?

Answer 24

x2000

Question 25

Explain how electron microscopes work.

Answer 25

They use a beam of fast travelling electrons (wavelength about 0.004nm) that are fired from a cathode and focused, by magnets.

Question 26

Explain the types of images produced by electron microscopes.

Answer 26

They give clear and highly magnified images, especially compared to optical microscopes.

Question 27

In preparation for use by a TEM microscope, explain what has to happen to the specimen in preparation.

Answer 27

The specimen has to be chemically fixed by being dehydrated and stained.

Question 28

Explain how transmission electron microscopes work.

Answer 28

The beam of electrons shot by the cathode pass through the specimen (that’s stained with metal salts) and some of the electrons pass through and are focused onto the screen/ photographic plate.

Question 29

Explain the electron micrograph that TEM’s produce.

Answer 29

They form 2D black and white images.

Question 30

What is the maximum magnification formed by TEM’s.

Answer 30

x2million.

Question 31

Explain how the specimen for SEM microscopes must be prepared.

Answer 31

The electrons shot by the cathode don’t pass through the specimen (which is whole) as the electrons bounce off and are focused on the screen.

Question 32

Explain the image that SEM’s give.

Answer 32

The images produced are black and white and are 3D. Computer software programmes can also add false colour.

Question 33

List three disadvantages that are with both types of electron microscopes.

Answer 33

> very large.
very expensive.
need a great deal of skill and training to use.

Question 34

Specimens used for electron microscopes have to be _____ when used in the microscopes.

Answer 34

Dead.

Question 35

What are the effects the metallic salt stains used for staining can have on humans?

Answer 35

They can be potentially hazardous for humans.