An example of an analogy used in popular science writing:
"Certainly a bacterium, which through all its life is tossed around by molecular impacts, will sneer at the statement that heat cannot go over into mechanical motion! … For a bacterium, which is not much larger than the molecules themselves, the difference between the thermal and mechanical motion has practically disappeared, and it would consider the molecular collisions tossing it around in the same way as we would consider the kicks we get from our fellow citizens in an excited crowd."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
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This passage could be seen as anthropomorphic, in suggesting that a bacterium (a single celled entity with no nervous system) could sneer or give consideration to water molecules colliding with it.
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The suggestion that a bacterium is not much larger than the molecules colliding with it could be misleading. Some learners will have the alternative conception that cells may not be so much bigger than atoms (read 'The cell nucleus is probably bigger than an atomic nucleus: A cell is about ten times larger than an atom'), but a quick 'back-of-the-envelope' calculation suggests that if a bacterium is of mass c.1.7 x 10-13g (a value given for E. coli in one research paper) then as the mass of a water molecule is 18g/NA or c.3 x 10-23g which would suggest each bacterium is about the mass of 5 000 000 000 water molecules. By most reasonable uses of language a bacterium is much larger than the molecules.
Read about the nature of alternative conceptions
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