Gravitaxis
Gravitaxis is the reaction of a freely moving organism to gravity. It induces an oriented movement of the organism either in the direction of the gravity vector (= positive gravitaxis) or against the gravity vector (= negative gravitaxis). In older publications the term geotaxis is also used (because of the direction of the earth's gravity vector ).
Higher living beings, such as humans, have complex sense organs for this, especially in the ear. Protozoa such as Euglena gracilis - from the genus of the ophthalmic animals ( Euglena ) - can perceive the direction of gravity without the aid of complex organs. In many animal phyla, gravity is perceived by statocysts as special sensory organs. Gravitaxis can also result from a purely physical mechanism, so that a perception of the direction of gravity via special organs is not necessary. One example is microorganisms in which the center of gravity is shifted to one end of the organism so that they align themselves antiparallel to the gravity vector, similar to a buoy. It has been shown that an asymmetry in the form of microorganisms can be sufficient to cause gravitaxis.
However, unicellular organisms need gravitaxis to get to light or to the surface of a body of water where solar radiation is most effective for photosynthesis. Through an interplay of gravitaxis and phototaxis , the organisms "regulate" themselves in the optimal range. Other organisms come to the surface with the help of gravitaxis in order to reproduce. The chance of meeting a partner is significantly higher there than in the depths of the water.
Web links
- Euglena gracilis as an oxygen producer in a bioregenerative life support system and its physiological response to changes in gravity - accessed November 8, 2016
- High Light Exposure Leads to a Sign Change of Gravitaxis in the Flagellate Euglena gracilis - accessed November 8, 2016
- Spaceflight Microgravity Reduced Photosynthetical Electron Transport and Altered Energy Distribution in Euglena gracilis - Retrieved November 8, 2016
Individual evidence
- ↑ B. ten Hagen, F. Kümmel, R. Wittkowski, D. Takagi, H. Löwen, C. Bechinger: Gravitaxis of asymmetric self-propelled colloidal particles . In: Nature Communications . 5, No. 1, 2014, p. 4829. doi : 10.1038 / ncomms5829 .