2.1.3: Methods of studying cells Flashcards
What is an object in terms of microscopy
Material put under the microscope
What is an image in terms of microscopy
Appearance of material when viewed with microscope
What is magnification in terms of microscopy
how many times bigger the image is when compared to the object
What is resolution in terms of microscopy
minimum distance apart two objects can be in order for them to appear separate in the image
What are the SI units for length and how do you convert between each
1000 nm = 1 micrometer
1000 micrometers = 1mm
1000 mm = 1 m
1000 m = 1 km
How do you calculate object size from image
length (mm) x 1000
/ magnification
how do you calculate magnification
length of scale (mm) x 1000
/ scale value
what is the image magnification object triangle
I
M O
What are the 3 types of microscopes
transmission electron, scanning electron, optical
Describe the advantages and disadvantages of an optical microscope
AD: living material, colour image
DISAD: low resolution
Describe the advantages and disadvantages of a transmission electron microscope
AD: very high resolution
DISAD: dead object, black and white 2D image, very thin object, image may contain artefacts
Describe the advantages and disadvantages of a scanning electon microscope
AD: high resolution, 3D image
DISAD: dead object, image may contain artefacts
how do optical microscopes work
wavelengths of light shining through glass lens and through the specimen, a dye is applied to the object, to see the specimen in colour
how do SEM work
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
how do TEM work
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
what is the advantage of electron microscopes compared to optical
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
what are all the labels on a microscope diagram
eyepiece, neck, arm, turn table, objective lens x 3, stage, stage clip, condenser, coarse focus and fine focus, light source, base
how do you calibrate your microscope
number of divisions on stage micrometer x length of each division (micrometers)
/ number of divisions on eyepiece graticule
= conversion factor (micrometers) (1 epu)
What is cell fractionation
process where cells are broken up and the different organelles contained within them are separated.
what conditions must the tissues be placed in before cell fractionation
tissues must be placed in a cold, buffered, isotonic solution
why should tissues be placed in a solution that is cold
to reduce enzyme activity that might break down the organelles
why should tissues be placed in a solution that is buffered
so that the pH doesn’t fluctuate and alter organelle structure or affect enzyme activity
why should tissues be placed in a solution that is isotonic
to prevent organelles bursting or shrinking as a result of osmotic gain or loss
what are the two stages of cell fractionation
homogenation, then ultracentrifugation
describe the process of homogenation in cell fractionation
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
describe the process of ultracentrifugation in cell fractionation
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
