Methods of Studing Cells

Question 1

What is the limitations of a light microscope?

Answer 1

Poor resolution > relatively long wavelength

Question 2

How do optical microscopes work and what are their benefits?

Answer 2

• Use light to from an image
• Specimen can be alive

Question 3

How do electron microscopes operate?

Answer 3

Fires beam of electrons at specimenn

Question 4

What are the 2 advantages of TEM?

Answer 4

• Electron beam is very short wavelength > resolve objects well > high resolving power
• Electrons are negatively charged > beam can be focused using electromagnets

Question 5

How does a TEM work?

Answer 5

• Electron gun produces beam of ele3ctrons > focused onto specimen by condenser electromagnet
• Beam passes through specimen > absorbs electrons > appears dark
• Other parts of the specimen allow electrons to pass through > appear bright

Question 6

What is the resolving power of the TEM?

Answer 6

0.1NM (high)

Question 7

What is the equation for magnification?

Answer 7

Image size over actual size

Question 8

What is magnification?

Answer 8

The degree to which the size of the image is larger than the object itself

Question 9

what is a disadvantage of the optical microscope?

Answer 9

Individual cells are transparent > components not visible without dye > staining usually kills cells

Question 10

How does the SEM operate?

Answer 10

Beam of electrons moves back and forth across cells surface > creating details of cell surface characteristics

Question 11

What are the benefits of SEMs?

Answer 11

• Can be 3D
• Specimen doesn’t have to be thin

Question 12

What are the disadvantages of SEMs?

Answer 12

Lower resolution than TEM

Question 13

What is resolution?

Answer 13

Ability to distinguish two adjacent structures as separate

Question 14

What are the steps of cell fractionation? (3)

Answer 14

1) Homogenisation
2) Filtration
3) Ultracentrifugation

> Process repeated (spin at higher speeds)

Question 15

What is the process of homogenisation? (3)

Answer 15

Cells keps under specific conditions

1) isotonic solution > no water potential for osmosis to occur which could cause organelles to shrink or burst

Question 16

What is the process of homogenisation? (3)

Answer 16

Cells keps under specific conditions

1) isotonic solution > no water potential for osmosis to occur which could cause organelles to shrink or burst

2) Ice cold > reduces enzyme activity

3) Buffered solution > pH at constant level to prevent damage to protein structure

Question 17

Describe filtration in cell fractionation (1)

Answer 17

Through a gauze which separates larger components and smaller organelles

Question 18

Describe the process of ultracentrifugation (2)

Answer 18

1) FILTERED SAMPLES are spun in a centrifuge > important each test tube directly opposite is balanced

2) Heavier components fall to the bottom, lighter to the top