2.1.2 Studying cells

Question 1

Resolution

Answer 1

How detailed an image is - how well a microscope can distinguish two points close together

Question 2

Magnification

Answer 2

How much bigger an image is than the specimen

Question 3

Optical microscope disadvantages/ advantages

Answer 3

• Max resolution of ≈ 0.2 μm
• Max magnification of ≈ x1500

-Cheap and portable

Question 4

SEM action

Answer 4

• Scan a beam of e- across specimen
• Knocks e- off which cathode ray tube picks up and forms image
• Shows surface of specimen and in 3D

Question 5

TEM action

Answer 5

• Electromagnets used to focus beam of e- through specimen
• Dense sections absorb more e- ∴ darker on image
• Higher res. but only on thin specimens

Question 6

How to prepare a temporary mount

Answer 6

• Pipette water onto slide
• Use tweezers to place thin section of specimen on water drop
• Add stain
• Add cover slip

Question 7

How to add a cover slip with no air bubbles

Answer 7

• Stand slip upright

- Tilt carefully onto specimen

Question 8

Steps in cell fractionation

Answer 8

• Homogenise into solution
• Filtration
• Ultracentrifugation

Question 9

How is homogenisation performed and why?

Answer 9

Vibrate/ grind cells to break plasma membranes and release organelles

Question 10

How is filtration performed and why?

Answer 10

Filter mixture through gauze to remove large debris

Question 11

Ultracentrifugation steps

Answer 11

1) Pour cell fragments in tube - centrifuge at lowest speed
2) Decant supernatant and pour into new tube
3) Centrifuge at higher speed
- Repeat

Question 12

Order organelles by density

Answer 12

Nuclei - Mitochondria - Lysosomes - Endoplasmic reticulum - Ribosomes