Studying cells Flashcards
What is magnification?
How much larger a sample appears to be compared to its actual size.
What is resolution?
The ability to distinguish between 2 separate points.
What is an optical microscope?
A beam of light is condensed to create the image.
What are the disadvantages and advantages of having optical microscopes?
D: low resolution due to having a longer wavelength, low magnification therefore organelles in cells are not visible.
A: coloured images, able to view live samples.
What are the 2 types of electron microscopes?
Transmission electron (TEM)
scanning electron (SEM)
How does a TEM work?
An electron gun produces a beam of electrons that is focused in the specimen, passing through a thin section appearing brighter, the denser areas aboard more electrons appearing darker.
What are the limitations of TEM’s?
- must be in a vaccum, therefore living specimens cannot be observed.
- a complex ‘staining’ process is required, and even then the image in not in colour.
- the specimen must be extremely thin.
What are SEM’s?
Scans a beam is passed back and forth across the surface of the specimen in a regular pattern, the electrons are scattered by the specimen, the pattern of this scattering depend on the contours of the specimens surface, building up a 3D image by computer analysis of the pattern of scattered electrons and secondary electrons produced.
What are the advantages and limitations of SEM’s?
A: can use thick specimens, allow external 3D structures to be produced.
L: low resolution, in a vaccum so cannot observe live specimens, produce no colour images.
What is cell fractionation?
Process of separating parts of a cell based on mass in order to study a specific organelle under a microscope.
What is required to do before cell fractionation?
• ice cold- prevents enzymes denaturing to break down organelle.
• isotonic- prevents organelles bursting or shrinking as a result of osmotic gain or dehydration.
• buffered- maintains ph levels for enzymes to not denature.
Explain the process of homogenisation?
Cells are broken up be a homogeniser to release the organelles from the cell. The resultant fluid (homogenate) is filtered through a gauze to remove any complete cells and large pieces of debris leaving a solution (filtrate).
Explain the process of ultracentrifugation?
The filtrate is spun in a centrifuge at a low speed so the heavier organelles settle at the bottom (pellet), the fluid suspended (supernatant) is then drained into a fresh tube and spun at a higher speed in the centrifuge to create a new pellet and the process continues.
