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Plant and Animal Cells
Clamydomonas is a single celled organism that lives under water. It can move
itself to the light to photosynthesise, and stores excess food as starch.
a) What features does it have in common with most plant cells?
b) What features are not like plant cells and what are they used for?
c) Would you class Clamydomonas as a plant cell or an animal cell? Explain
why.
It is possible to separate the different parts of a cell using a centrifuge which
spins around very fast rather like a spin dryer. They are used to separate
structures that might be mixed together in a liquid. One of their uses is to
separate the different parts of a cell.
The cells are first broken open so that the contents spill out into the liquid. The
mixture is then put into the centrifuge. The centrifuge starts to spin slowly and a
pellet forms at the bottom of the tube. This is removed. The rest is put back into
the centrifuge at a higher speed and the next pellet removed and so on.
Results
Centrifuge speed (rpm)
3000
10 000
12 000
Part of cell in pellet
nuclei
mitochondria
ribosomes
Rpm = revolutions per minute
a) Can you suggest a link between the speed of centrifuge and the size of the
part of the cell found in the pellet?
b) What apparatus would you need to test your idea?
c) What results would you expect if correct?
d) What would be the easiest measurement to make to show mitochondria
size?
e) Suggest how many mitochondria you might measure.
f) How would you calculate the mean for the measurement?