Why Can't the Paramecium Change Shape Like the Ameba?

February 15, 2024

Paramecium move in a variety of ways, but they can't change shape like the ameba. They are unicellular protists that live in ponds and puddles. They belong to the phylum Ciliophora and the kingdom Protista.

Their bodies are covered with tiny hair-like projections called cilia that whip back and forth in an aquatic environment. When the cilia encounter obstacles or unwanted chemicals, they cause the organism to undergo an avoiding reaction (Fig. 2A). This simple mechanism allows Paramecium to navigate in crowded multisensory environments.

When a paramecium approaches an obstacle, it first swims backward for a fraction of second while revolving around its long axis. Then the anterior end turns while the posterior end remains still, which causes the cell to shift its direction without actually touching the obstacle. The new direction is determined by a cellular sensor that may be linked to a particular type of chemoreceptor. Jennings speculated that this sensor is located in the oral groove, but recent studies have found it more likely to be located on the ectoplasm.

All paramecium species have one macronucleus, but the number of micronuclei varies among them. Forney explains that the macronucleus contains a subset of DNA that is passed to a daughter cell during binary fission or conjugation.

In both of these reproductive processes, one parent cell gives rise to two genetically identical offspring. Binary fission is the more common mode of asexual reproduction, but Paramecium can also reproduce sexually. Two complementary paramecia come together and exchange genetic material, then they separate. The process takes 50 times longer than asexual binary fission.

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