Amoeba and Paramecium: Structure, Movement & Reproduction
Obj 13: Functions of the Amoeba
Locomotion: It moves by issuing temporary protoplasmic extensions called pseudopodia. It moves in the direction of newly formed pseudopodia; continuous changes in the cell protoplasm produce amoeboidal movement.
Food
Food: Its diet consists of organic particles, algae, bacteria and other protozoa. Microorganisms or particles that come into contact with it are surrounded by pseudopodia and trapped in its digestive vacuole.
Respiration and Excretion
Respiration and excretion: These are simple processes: oxygen dissolved in the surrounding liquid medium is incorporated and carbon dioxide is removed by diffusion.
Reproduction
Reproduction: Reproduction occurs asexually through cell division or bipartition (binary fission).
Behavior
Behavior: Amoebae respond to external and internal stimuli; these responses constitute their observable behavior.
Paramecium: Free-Living Ciliate
The paramecium is a free-living single-celled organism covered with cilia. It is among the most common ciliates and is one of the best-studied protozoa morphologically and physiologically. Paramecium species serve as model organisms for the study of these protozoa.
It lives in fresh water, often in stagnant water and among decaying leaves. In laboratories, boiled straw in water is commonly used to culture them; after a few days a film (cuticle) forms on the surface of the container where paramecia are found.
The ciliates represent an evolutionary advancement within the protozoa.
Structure
Paramecia are elongated, about 0.15 to 0.30 mm long, with blunt ends and a characteristic shoe-like shape. They are protected by a membrane covered with cilia, which serve for movement and food capture.
Each cilium is anchored on a basal granule (basal body). Cilia are coordinated by transverse and longitudinal fibers that control their movement. Beneath the membrane are trichocysts, organelles involved in defense and other functions.
Locomotion
Locomotion: Paramecia move by the coordinated beating (vibration) of the cilia, enabling forward and backward movement.
Food
Food: Their diet includes protozoa, algae, bacteria and dissolved substances in the water. Food particles are directed toward the oral groove by ciliary action and ingested into food vacuoles.
Respiration and Excretion
Respiration and excretion: Paramecia take oxygen dissolved in the water where they live. They have no specialized respiratory organs; gas exchange (oxygen uptake and carbon dioxide removal) occurs by diffusion across the cell membrane.
Behavior
Behavior: When encountering a mechanical stimulus or an obstacle, paramecia exhibit avoidance responses and may use trial-and-error movements. Thermal stimuli provoke rapid responses, with greatest activity typically between 24 and 28 °C. Despite being unicellular, paramecia commonly divide into two by binary fission every 22 to 24 hours.
Reproduction
Reproduction: The most common method is asexual reproduction by binary fission (bipartition). More complex sexual processes occur by conjugation, involving exchange between two individuals.
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