Fractionation, Units And Microscopy Flashcards
The difference between magnification and resolution
Resolution is the minimum distance apart 2 objects can be to appear as separate items, magnification is how many times bigger the image is compared to the object
What is the formula to work out magnification
Magnification is size of image divided by size of actual object
The equation to work out size of object (actual)
Image over magnification
What is the process of cell fractionation
Where cells are broken up and the different organelles they contain are separated out.
Before fractionation can begin, what does the tissue have to be placed in and why
Cold- to reduce enzyme activity that might break down organelles, isotonic - to prevent organelles from bursting or shrinking and buffered- so pH doesn’t fluctuate and affect enzyme functioning
What are the two stages of cell fractionation
Homogenisation and ultracentrifugation
What happens during homogenisation
Cells are broken up, this releases the organelles from the cell, the fluid (homogenate) is then filtered to remove complete cells and debris
What happens during ultracentrifugation
The tube of filtrate is placed in a centrifuge and spun at a low speed, the heaviest organelles (nuclei) are forced to the bottom where they form a sediment. The fluid at the top is removed leaving sediment and the liquid is them spun at a faster speed
The principles of transmission electron microscopes
An electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet. Beam passes through thin section and parts absorb electrons and a photo is produced on a screen (photomicrograph) resolution (0.1nm)
Principles of scanning electron microscopes
Directs a beam of electrons on surface from above not below and beam is passed back and forth in a regular pattern. Also specimens don’t have to be thin as electrons don’t penetrate
How did scientific community distinguish between artefacts and organelles
Repeatedly preparing specimens in different ways, if object spotted with only 1 technique, then it is artefact
How would you work out the mitosis index
Number of cells in mitosis/ total number of cells
What is the resolving power of a light microscope
Limited to 0.2 um or 200nm
What are the advantages of Light microscope
Can see living specimens, easier specimen preparation, can have a variety of coloured stains
What are the disadvantages of a light kicro
Low resolution so less organelle detail and smaller components not visible
