3.1 Methods of Studying Cells

Question 1

What is magnification and how do you calculate it?

Answer 1

• how much bigger the image is than the specimen
• size of image/size of real object

Question 2

What is the resolution?

Answer 2

• how well a microscope distinguishes two points that are close together

Question 3

What are the two types of microscopes?

Answer 3

• optical
• electron

Question 4

List 3 things about an optical microscope

Answer 4

1.Use light to form an image
2. Maximum resolution of 0.2 micrometers
3. Maximum useful magnification is x1500

Question 5

List 3 things about an electron microscope

Answer 5

1.Electrons to form an image
2. Maximum resolution of 0.0002 micrometers 3. magnification is x1500000

Question 6

What are the two types of electron microscopes?

Answer 6

• transmission(TEM)
• scanning (SEM)

Question 7

List 4 things about TEM

Answer 7

1. use electromagnets to focus a beam of electrons which is transmitted through the specimen
2. Denser parts of specimen absorb more electrons which make the images look darker
3. Give high resolution images so you see internal organelle structure
4. Only be used on thin specimens

Question 8

List 4 things about SEM

Answer 8

1. Scan a beam of electrons across the specimen, knocking off electrons from the specimen which are gathered in a cathode ray tube to form an image
2. The images you end up with show the surface of the specimen and they can be 3D
3. SEM’s can be used on thick specimens
4. Give lower resolution image

Question 9

What are the 3 steps of cell fractionation?

Answer 9

1. Homogenisation
2. Filtration
3. Ultracentrifugation

Question 10

Describe homogenisation

Answer 10

• blend cell into a blender
• breaks up the plasma membrane and releases the organelles into a solution

Question 11

What are 3 things required during homogenisation?

Answer 11

1. Ice-cold = reduces enzyme activity in breaking down the organelles
2. Isotonic = same water potential to reduce osmosis and prevent cell damage
3. Buffer solution = maintain pH

Question 12

Describe filtration

Answer 12

• homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris like connective
• organelles are much smaller than the debris so they pass through the gauze
• left with a solution containing a mixture of organelles

Question 13

Describe ultracentrifugation

Answer 13

• tube of filtrate is placed in centrifuge and spun at a low speed
• heaviest organelles are forced to the bottom off the tube where they form a thin sediment = the pellet
• fluid at the top of pellet = supernatant is removed
• supernatant is a transferred to another tube and spun in centrifuge at a faster speed
• next heaviest organelles are forced to the bottom of the tube
• process is continued so at each increase in speed the next heaviest organelle is sedimented and separated out