Microscopes

Question 1

What does magnification mean?

Answer 1

How many times bigger an object appears compared to original image

Question 2

What is meant by “Linear Magnification”?

Answer 2

A specimen seen at a ×100 magnification will appear 100 times wider and longer than actual size

Question 3

What does resolution mean?

Answer 3

Ability an optical instrument has to produce an image distinguishing two objects next to each other

Question 4

Why is the development of optical microscopes important?

Answer 4

Supports cell structure understanding

Question 5

Where are optical microscopes used?

Answer 5

• Schools
• Colleges
• Hospitals
• Research laboratories

Question 6

What are the benefits of optical microscopes?

Answer 6

• Relatively cheap
• Easy to use
• Portable, usable in the field and laboratories
• Can study living specimens

Question 7

How are present-day optical microscopes similar to those from the 17th Century?

Answer 7

Both rely on lenses to focus light beam

Question 8

What is the maximum magnification for optical microscopes?

Answer 8

×1,500 - ×2,000 in some types.

Question 9

What can be seen using an optical microscope?

Answer 9

Some large cell structures clearly

Question 10

How is resolution limiting in optical microscopes?

Answer 10

Can’t magnify any higher while still giving a clear image

Question 11

What do optical microscopes use to function?

Answer 11

Visible light.

Question 12

What is the wavelength of visible light?

Answer 12

400-700nm.

Question 13

When will structures appear as one object when using an optical microscope?

Answer 13

When structures are smaller than 200nm.

Question 14

Why can’t ribosomes be seen using an optical microscope?

Answer 14

They’re too small, only 20nm in diameter.

Question 15

What is the method to using an optical microscope?

Answer 15

1. Place specimen on slide on stage and clip in place
2. Rotate nose piece so lowest power OL is over specimen
3. Adjust CFD while looking into eyepiece until image is focused
4. While viewing image, adjust iris diaphragm for optimum light
5. Ensure object viewed is directly over hole in stage
6. Rotate nose piece to ×10 OL over specimen, use ocular tube and FFD to focus image
7. Repeat using ×40 and ×100 OL if necessary

Question 16

How should a microscope be held?

Answer 16

Arm in one hand, base in other

Question 17

What is an electron micrograph?

Answer 17

A photo of image seen using electron microscope.

Question 18

What is meant by organelles?

Answer 18

Small structures in cells, each having specific functions.

Question 19

What is a photomicrograph?

Answer 19

Photo of image seen using optical microscope displayed on computer screen

Question 20

How is total magnification calculated?

Answer 20

Magnifying power of OL × magnifying power of EL.

Question 21

What is another name for a laser scanning microscope (LSM)?

Answer 21

Confocal microscope

Question 22

How do LSM work?

Answer 22

Use laser light to scan object point by point, assembling, by computer, pixel information into one image, displayed on computer screen

Question 23

What are the properties of LSM images?

Answer 23

• High resolution
• High contrast

Question 24

What is the significance of LSM’s having depth selectivity?

Answer 24

Can focus on structures at different depths in specimen, can observe whole living specimens and cells

Question 25

Why are LSM's used in medicine?

Answer 25

• Observe specimens to make efficient diagnosis earlier • More effective treatment can then be given

Question 26

How do electron microscopes work?

Answer 26

Using a beam of fast-travelling electrons (0.004nm); much greater resolutions and magnifications than optical microscopes, for highly magnified images.

Question 27

How are electrons fired in an electron microscope?

Answer 27

From a cathode and focused, by magnets, not glass, on a screen/photographic plate.

Question 28

Why do electron microscopes have a higher resolution than optical microscopes?

Answer 28

Fast-travelling electrons have a wavelength of about 125,000 times smaller than visible light spectrum

Question 29

How do transmission electron microscopes work (TEM's)?

Answer 29

• Electron beam passes through stained specimen, some focusing on screen/photographic plate • Electrons form 2D grey-scale image

Question 30

In TEM's, how is a specimen prepared?

Answer 30

Chemically fixed by dehydration and staining using metal salts

Question 31

When were SEM's developed?

Answer 31

During 1960's.

Question 32

What are properties of SEM's?

Answer 32

• Electrons don't pass through whole specimen • Secondary electrons bounce off specimen's surface and focused onto screen, giving 3D, grey-scale image • Specimen has to be placed in vacuum, often coated with fine film/metal

Question 33

What do TEM's and SEM's have in common?

Answer 33

• Large • Very expensive • Needs lots of training to use

Question 34

Why do SEM samples have to be dead?

Answer 34

Viewed in a vacuum

Question 35

Why does the user need to be careful when handling metallic salt stains used to stain specimens in electron microscopes?

Answer 35

Can be dangerous/hazardous to user

Question 36

What does logarithmic mean?

Answer 36

Scale goes up in steps

Question 37

What is the resolution of the human eye?

Answer 37

0.3-0.5mm.

Question 38

What are cones and how do they work?

Answer 38

Photosensitive cells in retina, working in bright light, producing a visual acuity

Question 39

How many cones per mm are in the human eye?

Answer 39

200,000.

Question 40

How many cones per mm are in an eagle's retina?

Answer 40

1 million.

Question 41

What magnification do TEM's have?

Answer 41

×2 million - ×50 million in new generation developments.

Question 42

What magnification do SEM's have?

Answer 42

×15 - ×500,000