studying cells Flashcards
why do organelles have different shapes when you look at them under a microscope
as sections are cut in different places
Why do mucus-secreting cells have many Golgi bodies and mitochondria?
Golgi modifies, transports, and secretes mucus.
Mitochondria provides ATP
name an advantage of using a SEM rather than a TEM
a SEM gives a 3D image
how do you measure length of a cell using an optical microscope
Measure length with eyepiece graticule
Calibrate the eyepiece graticule with a stage micrometer
Why does an electron microscope show more detail of cell structure that a light microscope
electrons have a higher wavelength
electron microscopes have a higher resolving power
Describe the principles of a TEM.
Electrons pass through thin specimen
Denser aprts absorb more electrons
So denser parts appear darker
Electrons have a short wavelength so give higher resolution
Describe the limitations of a TEM.
Cannot view living specimens Must be very thin Artefacts may be present Complex staining method Only 2D images
Give an advantage of using a TEM rather than a SEM
Higher resolution
Allows internal structures in cells to be seen
Allows the internal details of organelles to be seen
Describe how a temporary mount is made
Thin slice/section
Put on slide in water/stain/solution
Add cover slip lower slowly to avoid air bubbles
How could you determine the number of stomata on the bottom of a leaf?
Very thin to let light through
Count number of chloroplast in a field of view
Repeat and calculate mean
Describe how a sample of chloroplasts could be obtained from a homogenised plant tissue?
Centrifuge at low speed & gradually speed up.
Discard first pellet (cell debris)
Re-spin supernatant at higher speed
Continue until chloroplast pellet found
Identify as chloroplasts using an electron microscope
