Studying Cells

• Optical microscopes can be used to observe live specimens in colour with a low resolution
• Electron microscopes have a higher resolution than optical microscopes because electrons have a shorter wavelength than light
• Magnification = image / actual
• Magnification is the increase in viewed size of an object
• Resolution is the ability to distinguish between two close points
• To find the real size of an organism under the microscope, you must calibrate a stage micrometer against the eyepiece graticule to find the true length of each point on the graticule ruler
• A transmission electron microscope is 2 dimensional and has no colour, specimens must be dead and in a vacuum and artefacts are common due to the thin slicing of the object
• A scanning electron microscope is three dimensional and has no colour, specimens must be dead and exist in a vacuum
• A transmission electron microscope has a slightly higher resolving power than a scanning electron microscope
• The transmission electron microscope causes a black and white image - when dark, electrons have been absorbed by the object
• Tissue is homogenised and filtered before centrifugation
• Tissue is cut in a cold isotonic buffer to prevent pH change, reduce enzyme action and prevent changes in water potential
• Cells are split open when homogenised, releasing organelles
• By spinning at higher speeds, pellets of differently sized organelles can form, the supernatent contains smaller organelles such as ribosomes