Methods Of Studying Cells

Question 1

what is resolution?

Answer 1

the ability to distinguish between two points

Question 2

what is magnification?

Answer 2

how many times bigger the image is compared to the real object

Question 3

what is cell fractionation?

Answer 3

it enables individual organelle structures and functions to be studied
it’s also used to isolate different organelles so they can be studied

Question 4

how can we separate the cell components?

Answer 4

homogenisation, filtration, ultracentrifugation

Question 5

what is homogenisation?

Answer 5

cell is broken open to release contents and organelles

Question 6

what solution do the cells need to be broken up into?

Answer 6

cold, isotonic and buffered

Question 7

why does the solution have to be cold when we break down the cells?

Answer 7

to reduce enzyme activity which prevents damage to the organelles

Question 8

why do we need to reduce enzyme activity?

Answer 8

because when the cell breaks open enzymes are released which can damage organelles

Question 9

why does the solution have to be isotonic when we break down the cells?

Answer 9

to prevent osmosis as it could cause organelles to burst or shrivel

Question 10

what does isotonic mean?

Answer 10

same water potential as other organelles

Question 11

why does the solution have to be buffered when we break down the cells?

Answer 11

prevent damage to organelle

Question 12

what does buffered mean?

Answer 12

keep at a constant pH (neutral), to prevent the denaturing of enzymes

Question 13

what are the two types of electron microscopes?

Answer 13

transmission electron microscope, scanning electron microscope

Question 14

why do electron microscopes have a high resolving power?

Answer 14

the wavelength of light is short

Question 15

why do optical microscopes have a low resolving power?

Answer 15

the wavelength of light is too long
- so single layer of cells is required

Question 16

what is the formula for magnification?

Answer 16

image size/ size of real object

Question 17

what do transmission electron microscopes work?

Answer 17

electromagnets to focus a beam of electrons, which is then transmitted through the specimen

Question 18

what is the outcome of using a transmission electron microscope?

Answer 18

denser parts of the specimen absorb more electrons, which makes them look darker on the image

Question 19

what is an advantage of a transmission electron microscope?

Answer 19

give higher resolution images, allows us to view internal structures

Question 20

what is a disadvantage of a transmission electron microscope?

Answer 20

• can only be used on thin specimens
• can only be used on non-living specimens

Question 21

what do scanning electron microscopes work?

Answer 21

scan a beam of electrons across the specimen, this knocks off electrons from the specimen which are gathered in a cathode ray tube to form an image

Question 22

what is an advantage of scanning electron microscopes?

Answer 22

• can be used on thick specimens
• images shown can be 3-D

Question 23

what is an disadvantage of scanning electron microscopes?

Answer 23

• can only be used on non-living specimens
• gives lower resolution images than TEMs

Question 24

how to go from millimetre(mm) to micrometre(um)?

Answer 24

x1000

Question 25

how to go from micrometre to nanometre?

Answer 25

x1000

Question 26

how to go from cm to mm?

Answer 26

x10

Question 27

what is ultracentrifugation?

Answer 27

separating the individual organelles

Question 28

where is the filtered solution spun?

Answer 28

a centrifuge

Question 29

how does differential centrifugation work?

Answer 29

- centrifuge spins and centrifugal forces cause pellets of most dense organelles to remain at the bottom - centrifuge is first spun at low speeds, and is repeated at increasingly faster speeds - each time supernatant is removed a pellet of organelles is left behind - supernatant is put back into centrifuge and spun at faster speed

Question 30

what organelle is the most dense?

Answer 30

nuclei

Question 31

what organelle is the least dense?

Answer 31

ribosomes

Question 32

what is the order of organelles (most to least dense)?

Answer 32

nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, ribosomes

Question 33

what is the centrifuge first spun at?

Answer 33

low speed to remove more dense organelles

Question 34

what is left in the centrifuge tube after it is spun?

Answer 34

- a pellet(solid) - supernatant(liquid)

Question 35

what should you do when you draw images in microscopy?

Answer 35

- label - draw with continuous lines - no shading - add magnification

Question 36

describe how the student could use an eyepiece graticule to determine the mean diameter of stomata?

Answer 36

- measure each stomata using eyepiece graticule - calibrate eyepiece graticule to stage micrometer - take a number of measurements and calculate the mean

Question 37

what is an eyepiece graticule?

Answer 37

- remains constant and in eyepiece lens

Question 38

what is a stage micrometer?

Answer 38

- placed on the stage and has lengths to figure out the size of each division in eyepiece graticule

Question 39

what is reliability?

Answer 39

- how repeatable something is

Question 40

how can we improve reliability in magnification?

Answer 40

- use a smaller mag or do across more cells

Question 41

what is accuracy?

Answer 41

how close you are to true value

Question 42

how can we improve accuracy in magnification?

Answer 42

- larger resolution and smaller unit of measure

Question 43

what is validity?

Answer 43

- if you are claiming what you are measuring is true

Question 44

what are the properties of optical microscopes?

Answer 44

- low resolution and magnification - can be used on living specimens - can only be used on thin specimens