CELLS: Analysing Cell Components

Question 1

Magnification

Answer 1

How much bigger the image is than the specimen

Question 2

Resolution

Answer 2

How easily a microscope distinguishes between two points that are close together.

Question 3

What are the two main types of microscope?

Answer 3

Optical

Electron

Question 4

Optical microscope:

• How does it form an image?
• Maximum resolution?
• Maximum useful magnification?

Answer 4

• Forms an image using light
• Maximum resolution of 0.2 micrometres
• Max useful magnification = x 1500

Question 5

Electron microscope:

• How does it form an image?
• Maximum resolution?
• Max useful magnification?

Answer 5

• Uses electrons
• Higher resolution of about 0.0002 micrometres
• Max useful magnification x 1500000

Question 6

What are the 2 types of electron microscopes?

Answer 6

Transmission (TEMs)

Scanning (SEMs)

Question 7

How do TEMs work?

Answer 7

• Electromagnets focus beam of electrons that is transmitted through specimen.
• Denser parts absorb more = darker image

Question 8

What is a strength and limitation of TEMs?

Answer 8

+ High resolution images, so can see internal structures of organalles

• Thin specimens needed

Question 9

How do SEMs work?

Answer 9

• Scan beam of electrons across specimen.
• Knocks off electrons from specimen, which gather in cathode ray tube to form image
• Shows surface, 3D images

Question 10

What is a strength and limitation of SEMs?

Answer 10

+ Thick specimens

• Lower resolution images

Question 11

How do you convert from micrometres to mm?

Answer 11

Divide by 1000

Question 12

How do you prepare a temporary mount of a specimen on a slide?

Answer 12

1. Pipette small drop of water onto slide
2. Use tweezers to place thin specimen on top of water
3. Add a stain
4. Add cover slip to protect.

Question 13

How are organelles separated?

Answer 13

Using cell fractionation

Question 14

What are the 3 steps of cell fractionation?

Answer 14

• Homogenisation - break up cells
• Filtration - removes large pieces
• Ultracentrifugation - separates organelles

Question 15

What does homogenisation do?

Answer 15

Breaks up plasma membrane

Releases organelles into solution

Question 16

How might you homogenise cells?

Answer 16

Grinding cells in a blender

Question 17

In cell homogenisation, what must the solution be?

Answer 17

• Ice-cold - reduces enzyme activity
• Isotonic - prevents damage through osmosis
• Buffered - maintains pH

Question 18

Describe the process of filtration:

Answer 18

• Homogenised cell solution filtered through gauze
• Separates large cell debris or tissue debris from organelles.

Question 19

Describe the process of ultracentrifugation:

Answer 19

• Cell fragments poured into tubes
• Tube put in centrifuge + spun at low speed
• Heaviest organelles gather at bottom + form thick sediment (the pellet)
• Supernatent drained off into another tube + spun at higher speed
• Process repeats

Question 20

Pellet

Answer 20

Thick sediment at bototm of centrifuge formed from heaviest organelles

Question 21

Supernatent

Answer 21

Fluid above pellet in which the lighter organelles are suspended.

Question 22

What organelle is likely to be the first separated out in ultracentrifugation?

Answer 22

Nuclei

Question 23

What organelle is likely to be the second separated out in ultracentrifugation?

Answer 23

Mitochondria