Paramecium is a unicellular protozoan with a characteristic slipper-like shape. It undergoes both asexual and sexual reproduction. Under favorable conditions, Paramecium undergoes binary fission, an asexual reproduction method. It undergoes conjugation, a sexual reproduction method under unfavorable conditions. Binary fission of Paramecium is an example for transverse fission since its cytokinesis takes place along the transverse axis of the organism.
Key Areas Covered
1. What is Paramecium
– Definition, Facts
2. Why is the Division of Paramecium Cells Called Transverse Fission
– Binary Fission of Paramecium
Key Terms: Binary Fission, Cytokinesis, Meiosis, Paramecium, Transverse Fission
What is Paramecium
Paramecium is a unicellular eukaryote, which belongs to the phylum Ciliophora under the kingdom Protista. It lives mainly in freshwater and sometimes in decaying organic matter. One of the characteristic features of Paramecium is its slipper-like shape. The length of the organism is approximately 0.3 mm. The outer surface of the body of Paramecium is covered by cilia. A Paramecium cell consists of a large macronucleus and a micronucleus. Two types of vacuoles appear in Paramecium as food vacuoles and contractile vacuoles. The oral groove on one side of the organism forms the gullet, which ends with a cytostome.
Figure 1: Paramecium
The beating of cilia in water is responsible for the swim-like locomotion of Paramecium. The backward beats of cilia facilitate the forward movement while the forward beats of cilia facilitate the backward movement Cilia also help in moving food into the gullet. The ingested food is taken into the cell by forming food vacuoles, and digestion occurs inside them. The wastes are eliminated through the anal pore. Paramecium is sensitive to the changes in the environment such as temperature, light, chemicals, and touch.
Why is the Division of Paramecium Cells Called Transverse Fission
Paramecium undergoes binary fission in which a single parent cell is divided into two equal halves, each of which becomes a separate organism. Binary fission occurs in three steps. First, small nucleus divides into two daughter nuclei by meiosis and they move into the opposite poles of the cell. Then, the large nucleus also divides into two. Finally, the cytoplasm of the parent cell divides into two by cytokinesis. In Paramecium, the axis of cytokinesis is transverse to the longitudinal axis of the organism. Hence, the division of Paramecium is called a transverse fission.
Figure 2: Transverse Fission
The anterior half (the proter) of the organism forms one organism while the posterior half (the opisthe) forms another organism.
Conclusion
Paramecium is a protest, having a characteristic slipper-like shape. Its asexual reproduction method is called transverse fission since the cytokinesis occurs in the transverse axis to the longitudinal axis of the organism.
Reference:
1. “Paramecium Reproduction.” BiologyWise, Available here.
Image Courtesy:
1. “Paramecium diagram” By Deuterostome – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Some types of ciliate fission” By Deuterostome – Own work (CC BY-SA 4.0) via Commons Wikimedia (Cropped)
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