3.2.1.3 Methods of Studying Cells

Question 1

what is the magnification triangle

Answer 1

..I
AM

Question 2

what are the units and prefixes

Answer 2

Question 3

process of measuring a cell under a microscope

Answer 3

• measure the number of eyepiece units that the cell is using the graticule
• remove the slide and replace it with a stage micrometer on the same magnification
• align the eyepiece graticule with the stage micrometer
• count how many epu on the graticule correspond to a known measurement on the micrometer
• determine the length of one divisions on the eyepiece graticule using the stage micrometer
• multiply the number of epu by the calibration factor to get the actual size of the cell

Question 4

what are the different type of microscopes

Answer 4

• compound light microscopes
• transmission electron microscopes
• scanning electron microscopes

Question 5

features of the compound light microscope

Answer 5

PROCESS:
- ray of light is shone onto the back of sample slide and observed through a lens opposite the light
ADVANTAGES:
- cheap
- light and mobile
- can view living organisms, in colour
DISADVANTAGES:
- low magnification (x2000 max)

Question 6

features of the TEM/SEM

Answer 6

PROCESS:
- shoots a beam of electrons down the microscope and uses magnets to focus the beam
ADVANTAGES:
- MUCH higher magnification and resolution
- meant the difference between artefacts and organelles could be observed
- SEM: 3D image
DISADVANTAGES:
- expensive and large (can’t be used in the field)
- only observe dead specimens in black and white
- needs specialist skills to create slides

Question 7

what is cell fractionation

Answer 7

extracting individual cells to study under a microscope

Question 8

why is the cut-up tissue kept in a cold solution

Answer 8

to prevent the lysosome digestive enzymes from functioning

Question 9

why is the cut-up tissue kept in a buffered solution

Answer 9

to keep the pH the same so it stops the cells from denaturing

Question 10

why is the cut-up tissue kept in a isotonic solution

Answer 10

to equal water potential in cytoplasm so you avoid shrivelling from osmotic shock

Question 11

what is the method of cell fractionation

Answer 11

1 - tissue is cut-up and kept in a cold, buffered, isotonic solution
2 - cut-up tissue is further broken down by a homogeniser
3 - homogenised tissue is spun in an ultracentrifuge at low speed for 10 mins (1000x gravity)
4 - sediment 1 is produced from low ultracentrifuge
5 - spun again in ultracentrifuge at medium speed producing sediment 2
6 - spun again in ultracentrifuge at high speed producing sediment 3

Question 12

what is in sediment 1

Answer 12

nucleus - most dense organelle

Question 13

what is in sediment 2

Answer 13

chloroplasts, mitochondria

Question 14

what is in sediment 3

Answer 14

ribosomes - least dense organelle

Question 15

what is the rest of the product called that is not found in the sediment after each ultracentrifuge

Answer 15

supernatant 1,2 and 3