Simple question. It forms a pseudopod, and then flows in to it. But how does it move its material to form a pseudopod? And even so, if it is floating in water, what is it pushing against so that part of it holds still and part can move forward? It would be like trying to move while wearing ice skates by pushing your arms forward in the air: no net force is transferred.

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    $\begingroup$ History: in 9th grade, I badgered my Biology teacher until she finally said "I don't know!" in exasperation. I liked her, so I never did that again, but 35 years later, I still don't have the answer. $\endgroup$ – user17124 Oct 23 '15 at 21:53
  • $\begingroup$ they use ameoba locomotion or ameoba movement with their pseudopods. $\endgroup$ – user37345 Oct 16 '17 at 20:50

It has a cytoskeleton, a network of fibers stretched across the cell which it can shorten and expand (by adding or subtracting actin monomers which build them) in a coordinated manner to more-less arbitrary change shape.

According to this paper, on surfaces they generally can adhere to it using membrane protein structures, thus the locomotion occurs due to friction.

To swim, they generate bumps near the front end of the cell and move them towards the back, similarly to how a swimmer uses hands.

  • $\begingroup$ Wow, thanks. Another thing I can tick off from my childhood list, along with writing a maze generation program... How does it know "how" to do those things? Or where to go, or whatever? Oh, well. A billion years of evolution can't be wrong. $\endgroup$ – user17124 Oct 24 '15 at 0:58
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    $\begingroup$ @nocomprende They are using chemotaxis. This basically means that they follow a chemical gradient in their environment and move towards the signal. They have transmembrane receptors that are bound by the chemokine and signal into the interior of the cell. This polarizes the cell and causes the nucleation of the actin filaments towards the "front" of the cell. And if you think that it is cool for Amoeba, then you will find it interesting to know that many of the cells of our immune system move around our bodies in pretty much the same fashion. $\endgroup$ – AMR Oct 24 '15 at 6:27
  • $\begingroup$ @AMR It is amazing how much complex behavior you can get out of systems that are very simple. Put a few hundred billion nerve cells together and, voila! $\endgroup$ – user17124 Oct 24 '15 at 13:48