Protozoa

What is Protozoa?

Protozoa are single-celled, eukaryotic organisms that can either live freely or as parasites. There are around 65,000 species of protozoa. They lack a cell wall and have various cell structures performing functions similar to higher animals’ organs. Protozoa can cause diseases like malaria (Plasmodium), sleeping sickness (Trypanosoma), and trichomoniasis (Trichomonas).

General Characteristics of Protozoa

• Habitat: Protozoa live in water environments, both fresh and salty. Some live freely, while others are parasitic. They can be aerobic or anaerobic, found in places like the human intestine.
• Size and Shape: Protozoa vary in size from microscopic to visible. They lack a rigid cell wall, making them flexible and variable in shape.
• Cell Structure: They are unicellular with a eukaryotic cell structure. They have one or more nuclei and various organelles for different functions. The plasma membrane surrounds the cell, and some have a pellicle for shape and movement.
• Nutrition: Protozoa are heterotrophic, consuming food through phagocytosis. They have structures like pseudopodia for capturing food.
• Locomotion: Protozoa move using flagella, cilia, or pseudopodia. Sporozoa move slowly using subpellicular microtubules.
• Life Cycle: Protozoa alternate between a dormant cyst stage and a reproductive trophozoite stage.
• Reproduction: Mostly reproduce asexually through binary fission, with some capable of sexual reproduction.

Protozoa Classification and Examples

Protozoa are classified based on their structure and movement:

• Mastigophora (Flagellated Protozoans)
  • Characteristics: Use flagella for movement, covered by a pellicle.
  • Examples: Trypanosoma, Trichomonas, Giardia.

• Sarcodina (Amoeboids):
  • Characteristics: Move using pseudopodia, lack a definite shape.
  • Examples: Amoeba, Entamoeba.

• Sporozoa (Sporozoans):
  • Characteristics: Endoparasitic, no specialized movement organelles.
  • Examples: Plasmodium, Myxidium.

• Ciliophora (Ciliated Protozoans):
  • Characteristics: Move using cilia, have a fixed shape due to pellicle.
  • Examples: Paramecium, Vorticella.

Protozoan Diseases in Humans

Protozoa can cause diseases when they become parasites in humans, leading to illnesses like malaria, amoebic dysentery, and sleeping sickness. These protozoa can multiply in humans, spreading through contaminated water, food, or insect bites.

Diseases Caused by Bacteria

Bacterial diseases are caused by harmful bacteria releasing toxins. Examples include bacterial meningitis, diphtheria, tetanus, cholera, and tuberculosis.

Diseases Caused by Fungi

Fungal infections, or mycosis, are caused by fungi reproducing through spores. These infections can affect the skin, nails, or internal organs. Examples include ringworm, athlete’s foot, and candidiasis.

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