How do Amoeba Reproduce

1 Key excerpts on "How do Amoeba Reproduce"

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  eBook - ePub

  Order Out of Chaos

  Man's New Dialogue with Nature

  • Ilya Prigogine(Author)
  • 2017(Publication Date)
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    (Publisher)

  Figure A .) Starting as a population of isolated cells, they join to form a mass composed of several tens of thousands of cells. This “pseudoplasmodium” then undergoes differentiation, all the while changing shape. A “foot” forms, consisting of about one third of the cells and containing abundant cellulose. This foot supports a round mass of spores, which will detach themselves and spread, multiplying as soon as they come in contact with a suitable nutrient medium and thus forming a new colony of amoebas. This is a spectacular example of adaptation to the environment. The population lives in one region until it has exhausted the available resources. It then goes through a metamorphosis by means of which it acquires the mobility to invade other environments.

  The aggregation of cellular slime molds furnishes a particularly remarkable example of a self-organization phenomenon in a biological system in which a chemical clock plays an essential role. See Figure A .

  Figure A

  When coming out of spores the amoebae grow and multiply as unicellular organisms. This situation extends until food, principally furnished by bacteria, becomes scarce. Then the amoebae cease to reproduce and enter into an interphase that lasts some eight hours. At the end of this period the amoebae begin to aggregate around cells that behave as aggregation centers. The aggregation occurs in response to chemotactic signals emitted by the centers. The aggregate thus formed migrates until the conditions for the formation of a fruiting body are satisfied. Then the mass of cells differentiates to form a stalk surmounted by a mass of spores.

  In Dictyostelium discoideum, the aggregation proceeds in a periodic manner. Movies of aggregation process show the existence of concentric waves of amoebae moving toward the center with a periodicity of several minutes. The nature of the chemotactic factor is known: it is cyclic AMP (cAMP), a substance involved in numerous biochemical processes such as hormonal regulations. The aggregation centers release the signals of cAMP in a periodic fashion. The other cells respond by moving toward the centers and by relaying the signals to the periphery of the aggregation territory. The existence of a mechanism of relay of the chemotactic signals allows each center to control the aggregation of some 105

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