Studying Cells

Question 1

What two types of microscope are there?

Answer 1

• light / optical
• electron

Question 2

Magnification and Resolution of light microscopes

Answer 2

• uses light to form an image
• max resolution is around 0.2 micrometres
• max useful magnification is around x1500
• can be used to observe larger structures: nuclei, entire cells, mitochondria and chloroplasts

Question 3

Advantages of light microscopes

Answer 3

• smaller + relatively cheap
• specimen preparation is relatively straightforward
• can produce coloured images
• allows observation of living specimens

Question 4

Magnification and Resolution of electron microscopes

Answer 4

• uses electrons to form images
• max resolution of around 0.0002 micrometres
• max magnification from around x1 000 000 up to many millions
• can be used to observe smaller structures: cell membranes, ribosomes, the endoplasmic reticulum, lysosomes

Question 5

Disadvantages of electron microscopes

Answer 5

• large and expensive
• specimens must be prepared by a complex process
• specimens must be viewed in a vacuum - live specimens cannot be observed
• images are always black and white, however can be viewed in colour through artificial processing

Question 6

What are the two types of electron microscopes?

Answer 6

• transmission electron microscopes (TEMs)
• scanning electron microscopes (SEMs)

Question 7

How do TEMs work?

Answer 7

uses electromagnets to transmit a beam of electrons through a specimen; denser part of the specimen absorbs more electrons, making them appear darker in the final image

Question 8

Types of image that TEMs produce

Answer 8

• high resolution
• allow the internal structures within cells, and within organelles to be seen
• two dimensional

Question 9

How do SEMs work?

Answer 9

passes a beam of electrons across the surface of a specimen and then detect the rate at which the electrons bounce back

Question 10

Types of image that SEMs produce

Answer 10

• three dimensional
• show the surface of the specimens
• lower maximum resolution than TEMs

Question 11

How do light/optical microscopes work?

Answer 11

• light is directed through the thin layer of biological material that is supported on a glass slide
• light is focused through several lenses so that an image is visible through the eyepiece
• magnifying power of the microscope can be increased by rotating the high power objective lens into place