3.2.1.3 Methods Of Studying Cells Flashcards
What are unit conversions below millimetres?
There are 1000 nanometers in a micrometer
There are 1000 micrometers in a millimetre
What is the equation for magnification?
Size of image / size of object
Must be the same units
What is magnification?
The degree to which the size of an image is bigger than the size of an object
What is resolution?
The degree to which it is possible to distinguish between two objects that are very close together
What is a compound light microscope?
Light passed through a specimen, image formed on human retina, focused by glass lenses
Max magnification is about 1000, 500X better than the human eye
Resolves objects separated by 0.2 micrometers
Needs very thin specimens
Can be stained to show colours
Is portable
What is an electron microscope?
Electrons are absorbed or deflected by molecules in air so a near vacuum has to be created
Beam can be focused using electromagnets because electrons are negatively charged
Greater resolving power is due to the electron beam having a shorter wavelength than light
What is a transmission electron microscope?
Consists of an electron gun, electrons pass through the specimen, beam is focused by magnetic lenses, image formed by fluorescent screen
Max magnification is millions
Resolves objects separated by 0.02 nanometers
Specimen must be extremely thin to allow electrons to penetrate
Complex staining process doesn’t create a coloured image
The high powered electron beam can destroy the specimen
Image may contain artefacts
What is a scanning electron microscope?
Specimens don’t need to be thin as electrons don’t penetrate
Specimen is sprayed with a thin coating of metal, electron beam is scanned across the surface of the specimen, metal emits secondary electrons
Emitted electrons can be focused by magnetic lenses
Image formed on fluorescent screens
Resolving power of 20nm, 10X better than light microscope
Creates a 3D image that is created by a computer analysis of the scattered electrons
What is a centrifuge?
It is a device that spins very fast in order to separate liquids into their different masses
What is differential centrifugation?
It is the separation of the different organelles within the cell
What is homogenation?
It is the process of blending cells
Homogenation is the resultant fluid
What is the method for differential centrifugation?
Cut tissue in an ice-cold isotonic buffer (cold to stop enzyme activity, isotonic to stop osmosis, buffer to stop pH changes)
Grind tissue in a filter to break down cells
Filter to remove insoluble cells
Place in a centrifuge at different speeds to separate the components
What are the vague speeds for separation in differential centrifugation?
Low = nuclei Faster = mitochondria and chloroplasts Faster = ER, Golgi and other membrane fragments Fastest = ribosomes
