I'm not talking about single celled organisms, but actual cells in your body. Is there any evidence that they can learn to, say, navigate an environment or avoid an aversive stimulus like an animal could? Is their behaviour understood well enough to say that it's entirely mechanistic, or are there things we still don't know?
For this specific question, let's divide the cells into two categories:
Cells that rarely "navigate" are the cells that are connected to give the tissue its mechanical properties. How do these avoid an "adverse stimulus"? Well, they don't avoid it. But if that stimulus "harms" cells they react in some way:
- if the cell is destructed by the pathogen, it will release chemical compounds that have chemotactic properties and attract specialized cells.
- if the pathogen has intracellular tropism, the cell may release some chemical compounds (see interferon) to "alert" other cells that something is wrong. Most cells can also present antigens on their surface.
- there are also some stimuli which change cellular life cycle turning cells into cancerous cells. These cells can gain excretory properties and produce substances that destroy intercellular jonctions. This is how metastases occur.
Cells that "navigate" are the blood cells. White blood cells respond to different kind of stimuli (chemical) in two ways: either they are attracted (by inflammatory cytokines for example) either they are repelled. Macrophages are attracted by cytokines released when a pathogen agent triggers inflammatory response. They "ingest" that pathogen through phagocytosis and expose some parts of it (the antigens) on their surface receptors. This stimulates lymphocytes which process that antigen and decide if it is self or non-self. If it is non-self, they stimulate proliferation of specialized cells against that antigen. Another type of blood cells, the platelets, although they have no nucleus, have interesting properties: they can adhere to the broken endothelium where they change shape and start to produce different chemical mediators.
Read more on:
- Wikipedia contributors, "Chemotaxis," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Chemotaxis&oldid=600637322 (accessed June 28, 2014).
- Wikipedia contributors, "Interferon," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Interferon&oldid=608718450 (accessed June 28, 2014).
- Wikipedia contributors, "Adaptive immune system," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Adaptive_immune_system&oldid=612379171 (accessed June 28, 2014).
- Wikipedia contributors, "Platelet," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Platelet&oldid=614627651 (accessed June 28, 2014).