2.1.3: Methods of studying cells

Question 1

What is an object in terms of microscopy

Answer 1

Material put under the microscope

Question 2

What is an image in terms of microscopy

Answer 2

Appearance of material when viewed with microscope

Question 3

What is magnification in terms of microscopy

Answer 3

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

Question 4

What is resolution in terms of microscopy

Answer 4

minimum distance apart two objects can be in order for them to appear separate in the image

Question 5

What are the SI units for length and how do you convert between each

Answer 5

1000 nm = 1 micrometer
1000 micrometers = 1mm
1000 mm = 1 m
1000 m = 1 km

Question 6

How do you calculate object size from image

Answer 6

length (mm) x 1000
/ magnification

Question 7

how do you calculate magnification

Answer 7

length of scale (mm) x 1000
/ scale value

Question 8

what is the image magnification object triangle

Answer 8

I
M O

Question 9

What are the 3 types of microscopes

Answer 9

transmission electron, scanning electron, optical

Question 10

Describe the advantages and disadvantages of an optical microscope

Answer 10

AD: living material, colour image
DISAD: low resolution

Question 11

Describe the advantages and disadvantages of a transmission electron microscope

Answer 11

AD: very high resolution
DISAD: dead object, black and white 2D image, very thin object, image may contain artefacts

Question 12

Describe the advantages and disadvantages of a scanning electon microscope

Answer 12

AD: high resolution, 3D image
DISAD: dead object, image may contain artefacts

Question 13

how do optical microscopes work

Answer 13

wavelengths of light shining through glass lens and through the specimen, a dye is applied to the object, to see the specimen in colour

Question 14

how do SEM work

Answer 14

specimen has to be in a vacuum so no air particles interfere in the electron beam therefore specimen has to be dead, electrons are scattered, image goes through a computer which produces a colour 3D image

Question 15

how do TEM work

Answer 15

specimen has to be in a vacuum so no air particles interfere in the electron beam therefore specimen has to be dead, electrons are transmitted through the specimen therefore specimen must be very thin

Question 16

what is the advantage of electron microscopes compared to optical

Answer 16

electron microscopes have much greater resolution and greater magnification as the electron beam has a much shorter wavelength than a beam of light, therefore you are able to see the ultrastructure of the cells

Question 17

what are all the labels on a microscope diagram

Answer 17

eyepiece, neck, arm, turn table, objective lens x 3, stage, stage clip, condenser, coarse focus and fine focus, light source, base

Question 18

how do you calibrate your microscope

Answer 18

number of divisions on stage micrometer x length of each division (micrometers)
/ number of divisions on eyepiece graticule
= conversion factor (micrometers) (1 epu)

Question 19

What is cell fractionation

Answer 19

process where cells are broken up and the different organelles contained within them are separated.

Question 20

what conditions must the tissues be placed in before cell fractionation

Answer 20

tissues must be placed in a cold, buffered, isotonic solution

Question 21

why should tissues be placed in a solution that is cold

Answer 21

to reduce enzyme activity that might break down the organelles

Question 22

why should tissues be placed in a solution that is buffered

Answer 22

so that the pH doesn’t fluctuate and alter organelle structure or affect enzyme activity

Question 23

why should tissues be placed in a solution that is isotonic

Answer 23

to prevent organelles bursting or shrinking as a result of osmotic gain or loss

Question 24

what are the two stages of cell fractionation

Answer 24

homogenation, then ultracentrifugation

Question 25

describe the process of homogenation in cell fractionation

Answer 25

cells broken up by a homogeniser (blender) to release organelles, resultant fluid = homogenate, this is filtered to remove any complete cells/large pieces of debris

Question 26

describe the process of ultracentrifugation in cell fractionation

Answer 26

fragments in the homogenate are separated by spinning them in a centrifuge, homogenate spun at low speed forcing heaviest organelles (nuclei) to the bottom where they form a pellet, fluid remaining at top of tube (supernatant) is removed and transferred to another tube, supernatant spun in next tube at faster speed, next heaviest organelles are forced to bottom to form pellet. REPEAT CYCLE