3.1 Methods of studying cells Flashcards
Define magnification
The number of times greater an image is than the size of the real(actual) object
What is the formula for Magnification
Size of image/ Size of real object=Magnification
Define resolution
The minimum distance 2 objects can be to be distinguished as separate objects
What are the characteristics of the optical microscope
(10)
- Light is focused using glass lenses
- Light passes through specimen differnet structures absorb different amounts of light and wavelengths
- Generates a 2D image of a cross section
- Low resolution due to long wavelength of light
- Cant see internal structures of organelles or ribosomes
- The specimen is thin
- Low magnification (x1500)
- Can View living organisms
- Simple preparations
- Can show colour
What are the characteristics of the Transmission electron microscope
(10)
- Electrons focused using electromagnets
- Electrons pass through specimen, Denser parts absorb more and appear darker
- Generates a 2D image of a cross section
- Very high resolution due to short wavelength of electrons
- Can see internal strctures of organelles and ribosomes
- Specimen= very thin
- High magnification (1,000,000)
- Can onlu view dead/dehydrated specimens as a vacuum
- Complex preparations so artefact often present
- Does not show colour
What are the characteristics of the scanning electron microscope
(10)
- Electrons focused using electromagnets
- Electrons deflected/ bounce off specimen surface
- Generates a 3D image
- High resolution due to short wavelength of electrons
- Cant see internal strcutres
- Specimen does not need to be thin
- High magnification (x1,000,000)
- Can only view dead/dehydrated specimens as it uses a vacuum
- Complex preparations so artefacts are present
- Does not show colour
What is an artefact
Artefacts are visible details that aren’t part of the specimen being observed, such as air bubbles or fingerprints
Describe how the size of an object viewed with an optical microscope can be measured
- Line up eyepiece granule with stage micrometre
- Calibrate eyepiece graticule- use stage micrometre to calculate size of divisions on eyepiece graticule
- Take micrometre away and use graticule to measure how many divisions make up the object
- Calculate the size of object by multiplying numbers of divisions by size of divison
- Recalibrate eyepiece graticule at different magnifications
What is cell fractionation
The process where cells are broken up and the different organelles they contain are separated out
What are the conditions required for Cell fractionation to take place
The tissue must be in a cold, buffered and isotonic solution
Why must the cell fractionation require the solution to be cold
To reduce enzyme activity that might break down the organelles
Why must the cell fractionation require the solution to be isotonic
Isotonic-Any external solution that has the same solute concentration and water concentration compared to body fluids. In an isotonic solution, no net movement of water will take place
So water does not move in or out of organelles by osmosis
also so they do not burst
Why must the cell fractionation require the solution to be Buffered
A buffer solution is one which resists changes in pH
To keep the pH constant–>so enzymes dont denature
What are the two stages to cell fractionation
Homogenation and ultracentrifugation
What is a homogeniser
A blender
Why is a homogeniser needed
It disrupts the cell membrane, breaking open cells and releasing organelles
What happens to the resultant fluid in the homogeniser
It is filtered to remove an ocmplete cells and large pieces of debris
Homogenate= reslutalnt fluid from the homogneiuser
What is ultracentrifugation
The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge
What is the process of ultracentrifugation
(6)
- The filtrate is placed (ina tube) in the centrifuge and spun at low speeds
- The heaviest organelles,nuclei, are forced to the bottom (of the tube) where they form a thin sediment or pellet
- The fluid at the top of the test tube (supernatant) is removed
- The supernatant is transferred to another tube and spun in the centrifuge at a faster speed
- The next heaviest organelle is forced to the bottom of the tube
- Repeat this process and the speed is increased every time
