Invertebrates (Chapter Series)

Author: Dr. Zorawar Singh

Amoeba proteus is a large, single-celled freshwater protist renowned for its shape-shifting ability. It moves and feeds using pseudopodia—temporary projections of its cytoplasm—that extend and retract through cytoplasmic streaming. This flexible movement, called amoeboid motion, allows it to engulf food like bacteria and smaller protists via phagocytosis. Found in nutrient-rich ponds and ditches, it maintains osmotic balance with a contractile vacuole that expels excess water. Despite its simplicity, Amoeba proteus exhibits complex cellular processes, including digestion, excretion, and reproduction through binary fission. It lacks a fixed shape or rigid structure, making it a classic example of eukaryotic cellular adaptability and a frequent subject in biological studies.

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Paramecium is a ciliated, single-celled protist commonly found in freshwater environments. It moves using hair-like structures called cilia and feeds on bacteria and algae through oral grooves via phagocytosis. With a unique dual-nucleus system—micronuclei for reproduction and macronuclei for daily functions—it reproduces asexually by binary fission and can exchange genetic material through conjugation. Its contractile vacuoles regulate water balance, and trichocysts provide defense.

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Plasmodium is a genus of parasitic protists responsible for malaria, a life-threatening disease affecting millions worldwide. Transmitted through the bite of infected female Anopheles mosquitoes, Plasmodium species—including P. falciparum, the most deadly—invade human liver cells and then red blood cells, where they multiply and destroy the host cells, causing cycles of fever, chills, and anemia. The parasite’s complex life cycle involves both sexual reproduction in mosquitoes and asexual replication in humans. Plasmodium evades the immune system by altering surface proteins. Despite advances in prevention and treatment, malaria remains a major global health challenge, particularly in tropical and subtropical regions, highlighting the need for vaccines, effective drugs, and vector control strategies.

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