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From my understanding, single celled organisms have been seen avoiding, and chasing, potential food or other organisms.

How do they accomplish this? They do not have eyes or ears or a nervous system. My understanding is that chemical reactions are involved somehow.

How do single-celled predators chase other cells? What happens on a chemical level?

Edit:To help keep a more constrained question, the single-celled organism I am considering is Paramecium

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  • $\begingroup$ This is actually a very broad question. Chemotaxis (the response to changes in a chemical in the environment) is only one of the "taxis". If you could refine this, say by singling out one single celled predator, I think it would be a less broad question. $\endgroup$
    – anongoodnurse
    Aug 10 '15 at 16:00
  • $\begingroup$ @anongoodnurse I am trying to find a common predatory Ciliate that does the behavior that I have described - is Paramecium a good example? $\endgroup$
    – DoubleDouble
    Aug 10 '15 at 16:11
  • $\begingroup$ Yes, paramecium is a good example. $\endgroup$
    – anongoodnurse
    Aug 10 '15 at 16:13
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    $\begingroup$ it is always useful to show work you've done yourself to answer the question. $\endgroup$
    – aaaaa says reinstate Monica
    Aug 10 '15 at 16:35
  • $\begingroup$ @aaaaaa my work so far is essentially google searches leading to links which fail to answer the question. All I can find is definitions of "single-celled organisms", "paramecium", or broad explanations of the digestive system. $\endgroup$
    – DoubleDouble
    Aug 10 '15 at 17:00
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Detection of and movement according to a gradient of a chemical species is a strategy that single cells use to track a target across space. There are very many strategies of movement depending on the cell and its environment, but a common problem that while cells can sense the concentration of chemicals, they cannot sense its gradient (the direction in which it increases) because they are of too small a size to rely on the difference of concentration on one side and the other. Howard Berg and his co-workers have discovered a mechanism that allows single cells to move toward increasing concentration zones by a combination of concentration sampling and movement. See his webpage, http://www.rowland.harvard.edu/labs/bacteria/projects/track.php

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