Microscopes Flashcards
Define magnification
the degree to which the size of an image is larger than the object itself
Define resolution
The minimum distance apart that 2 objects can be in order for them to appear as separate items
What part of the microscope is used to measure size of cells or objects?
Eyepiece graticule
What is cell fractionation?
the process where cells are broken up (lysed) and the different organelles within the cells are separated out
How is the tissue prepared for fractionation?
The tissue is placed in a cold, buffered solution with the same water potential as the tissue
Stages of cell fractionation?
- Homogenisation - this breaks open the cells, usually done either by vibrating the cells or grinding them up in a homogeniser (blender). This releases the organelles from the cells.
- Filtration - the resulting fluid (homogenate) is filtered to remove any debris (whole cells or large bits of remaining tissue)
- Ultracentrifugation - the fragments in the filtered homogenate are separated in a centrifuge at increasing speeds
Why does the solution have to be cold?
to reduce enzyme activity (in the tissue) that could break down the organelles
Why does the solution have to be buffered?
so that the pH doesn’t fluctuate (buffer - a solution which resists changes in pH when acid or alkali is added to it). A change in pH could affect organelles and enzymes (denatures proteins)
Why does the solution have to have the same water potential as the tissue?
to prevent organelles bursting or shrinking as a result of osmotic loss or gain of water
What affects resolving power?
Wavelength of light used by the microscope - shorter wavelength = higher resolution
What are artefacts?
Things seen under the microscope that aren’t part of the specimen e.g dust
Which microscope cannot produce 3D images?
Transmission electron microscope (TEM)
