Studying Cells

Question 1

Resolution

Answer 1

Ability to distinguish between two points

Question 2

Magnification

Answer 2

How many times larger an image is compared to an object

Question 3

How an optical microscope works

Answer 3

Light passes through a specimen

focused through glass lenses which can project a magnified image.

Question 4

Max resolution and magnification of optical microscopes

Answer 4

Resolution = 0.2 micrometers
Magnification = 1500x (useful)

Question 5

Conditions required for viewing slides under an optical microscope

Answer 5

Thin / single layer of cells
Stain (potassium iodide )

Question 6

Preparing a temporary mount

Answer 6

Pippette a drop of water (keeps specimen flat)
Use tweezers to place a thin layer of tissue cell,
Add a drop of stain
Use mounting needle to lower cover slip

Question 7

Advantages of optical microscopes

Answer 7

Can see living specimen
Can view specimen in colour
Slides are quicker to prepare

Question 8

Disadvantages of optical microscopes

Answer 8

Lower resolution
Can’t view smaller organelles in detail
Lower magnification

Question 9

How does a transmission electron microscope work?

Answer 9

Beams of electrons pass through the specimen
Electronic pass through less dense parts more easily
Scattered electrons are captured on a photographic plate

Darker parts = more dense

Question 10

Magnification and resolution of TEM

Answer 10

Magnification = x 250 000

Resolution = 2 nanometers

Question 11

How does a scanning election microscope work?

Answer 11

Specimen coated in a layer of metal
Electromagnet focuses beam of elections
Electrons bounce of surface on to photographic plate

Question 12

Magnification and resolution of SEM

Answer 12

Magnification = x100 000

Resolution = 3-20 manometers

Question 13

Advantages of electron microscopes

Answer 13

Higher resolution
Higher magnification
Can produce 3D images (sem)

Question 14

Why do electron microscopes have a higher resolution than optical microscopes?

Answer 14

Electron beams have a shorter wavelength than light

Question 15

Disadvantages of election microscopes

Answer 15

Must be in a vacuum
Can’t new living specimen
Not in colour
Complex staining process
Must be a very thin specimen (tem)

Question 16

Comparisons between TEM and SEM

Answer 16

SEM has a lower resolving power than TEM

TEM produces 2D images but SEM produces 3D images

Question 17

Cell fractionation

Answer 17

Process where cells are broken up and the different organelles they contain are separated

Question 18

Why is tissue placed in cold, isotonic, buffered solutions during homogenation?

Answer 18

Cold = reduce/ stop enzyme activity

Isotonic = prevents osmosis

Buttered = controlled pH prevents enzyme denature and organelle damage

Question 19

Steps of cell fractionation and ultracentrifugation

Answer 19

Tissue is minced and placed in cold, isotonic, buffered solution
Homogeniser grinds into smaller pieces (releases organelles)
Homogenate is filtered (removes whole cells and large debus)
Suspension of homogenate is centrifuged in a test tube
Centrifuge at a lower speed so larger fragments (nucleus) collect at the bottom and smaller fragments suspended in supernatant
Sediment pellet removed and rest of supernatant is re-spun at higher speed
Mitochondora/chloroplast will collect next

Question 20

Differential centrifugation

Answer 20

Process involved in centrifuging at different speeds