Methods of Studying Cells

Question 1

what is an object?

Answer 1

material put under a microscope

Question 2

what is an image?

Answer 2

the appearance of the object when viewed under a microscope

Question 3

magnification =

Answer 3

size of image divided by size of object

Question 4

resolution definition

Answer 4

the minimum distance apart that two objects can be for them to appear as separate items under a microscope

Question 5

what does the resolving power of a microscope depend on?

Answer 5

the wavelength or form of radiation used

Question 6

what does a greater resolution produce?

Answer 6

a clearer and more precise image

Question 7

does increasing magnification always increase the resolution?

Answer 7

no - there is a limit

Question 8

what happens if you increase the magnification past the limit of the resolution?

Answer 8

the image will get larger but more blurry

Question 9

what is homogenisation?

Answer 9

breaking up cells in a blender (homogeniser) to release the organelles

Question 10

what is another name for the resultant fluid of homogenisation?

Answer 10

homogenate

Question 11

what happens to the homogenate?

Answer 11

it is filtered to remove complete cells and unwanted debris

Question 12

ultracentrifugation definition

Answer 12

the process by which fragments in a filtered homogenate are separated in a centrifuge

Question 13

what is the importance of cell fractionation?

Answer 13

obtaining large numbers of isolated organelles allows scientists to study their structure and function

Question 14

cell fractionation step 1

Answer 14

place tissue in a cold, buffered, isotonic solution

Question 15

why is the solution cold?

Answer 15

to reduce enzyme activity that might break down the organelles

Question 16

what is isotonic?

Answer 16

same water potential

Question 17

why is the solution isotonic?

Answer 17

to prevent organelles bursting/shrinking due to osmotic gain/loss of water

Question 18

why is the solution buffered?

Answer 18

to maintain pH to retain the integrity of the organelles

Question 19

cell fractionation step 2

Answer 19

homogenise the solution

Question 20

cell fractionation step 3 (and the first step of ultracentrifugation)

Answer 20

spin the homogenised tissue in a centrifuge at a low speed (1000 X gravity) for 10 minutes. Filter the homogenate to remove unwanted debris.

Question 21

what does a centrifuge create?

Answer 21

a centrifugal force

Question 22

cell fractionation step 4 (and the second step of ultracentrifugation)

Answer 22

spin the supernatant (left over) at a medium speed (3500 X gravity). Filter the homogenate to remove unwanted debris.

Question 23

cell fractionation step 5 (and the third step of ultracentrifugation)

Answer 23

spin the new supernatant at a high speed (16500 X gravity)

Question 24

what is removed at each increase in speed during ultracentrifugation?

Answer 24

the next heaviest organelles

Question 25

what is the heaviest organelle?

Answer 25

nucleus

Question 26

what is the lightest organelle?

Answer 26

ribosomes

Question 27

what is the second heaviest organelle?

Answer 27

chloroplasts

Question 28

what is the second lightest organelle?

Answer 28

ER

Question 29

what is the third heaviest organelle?

Answer 29

mitochondria

Question 30

what is the third lightest organelle?

Answer 30

lysosomes

Question 31

how does an optical microscope work?

Answer 31

light is sent from a light source through a specimen, the image of which is magnified by glass lenses

Question 32

what was the first type of microscope invented?

Answer 32

the light microscope

Question 33

what is the most common type of microscope?

Answer 33

the light microscope

Question 34

why are light microscopes the most common?

Answer 34

cheap, easy to use, can study living cells

Question 35

what type of image does a light microscope produce?

Answer 35

2D

Question 36

what is the resolution of a light microscope limited to?

Answer 36

200nm or 0.2 micrometers

Question 37

why is the resolution of a light microscope limited?

Answer 37

light has a relatively long wavelength

Question 38

what is the magnification of a light microscope limited to?

Answer 38

X 2000

Question 39

why are stains needed for objects under light microscopes?

Answer 39

individual cells are generally transparent and their components are not distinguishable unless they are coloured with special stains

Question 40

what is a problem with using stains?

Answer 40

it usually kills the cells

Question 41

what organelles can you see with a light microscope?

Answer 41

nucleus and mitochondria

Question 42

what do electron microscopes use instead of light?

Answer 42

a beam of electrons

Question 43

why do electron microscopes have a higher resolving power?

Answer 43

the electron beam has a shorter wavelength than light

Question 44

how is the image of an electron microscope produced?

Answer 44

specimens are not directly observed. A computer forms an image based on how many electrons are absorbed by different regions of the specimen

Question 45

what is the resolution of some of the best electron microscopes?

Answer 45

0.1 nm (2000X more than light)

Question 46

what are scanning electron microscope images created from?

Answer 46

the electrons that are reflected off the specimen

Question 47

how do both SEM and TEM work?

Answer 47

directs a beam of electrons at a specimen

Question 48

how is the beam of electrons focused?

Answer 48

electromagnets

Question 49

what are the images produced by SEM like?

Answer 49

3D and detailed

Question 50

do specimens have to be thin when using a SEM?

Answer 50

no

Question 51

Which has a slightly lower resolution: SEM or TEM?

Answer 51

SEM (1nm)

Question 52

why are SEM and TEM images black and white?

Answer 52

electrons don't correspond to light and colour. | Colour can be added artificially to these images

Question 53

what are some cons to using a SEM or TEM?

Answer 53

expensive | need training to operate it

Question 54

why must samples be dead for a SEM or TEM?

Answer 54

electrons can be deflected by molecules in the air so a vacuum is needed

Question 55

how are images from TEM created?

Answer 55

from the electrons that are absorbed by the specimen

Question 56

how is the magnification of TEM compared to SEM?

Answer 56

2X magnification of SEM

Question 57

what is the main con of a TEM?

Answer 57

sample must be thin