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protozoa
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Protozoa are single celled organisms. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. They live in a wide variety of moist habitats including fresh water, marine environments and the soil.
Some are parasitic, which means they live in other plants and animals including humans, where they cause disease. Plasmodium, for example, causes malaria. They are motile and can move by:
- Cilia – tiny hair like structures that cover the outside of the microbe. They beat in a regular continuous pattern like flexible oars.
- Flagella – long thread-like structures that extend from the cell surface. The flagella move in a whip-like motion that produces waves that propel the microbe around.
- Amoeboid movement – the organism moves by sending out pseudopodia, temporary protrusions that fill with cytoplasm that flows from the body of the cell.
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Protozoa are divided into four major groups based on the structure and the part involved in the locomotion: 1. Mastigophora or Flagellated protozoans: They are parasites or free-living. They have flagella for locomotion Their body is covered by a cuticle or pellicle Freshwater forms have a contractiRead more
Protozoa are divided into four major groups based on the structure and the part involved in the locomotion:
1. Mastigophora or Flagellated protozoans:
They are parasites or free-living.
They have flagella for locomotion
Their body is covered by a cuticle or pellicle
Freshwater forms have a contractile vacuole
Reproduction is by binary fission (longitudinal division)
Examples: Trypanosoma, Trichomonas, Giardia, Leishmania, etc.
2. Sarcodina or Amoeboids:
They live in the freshwater, sea or moist soil.
The movement is by pseudopodia. They capture their prey by pseudopodia
There is no definite shape and pellicle is absent
The contractile vacuole is present in the amoeboids living in freshwater
Reproduction is by binary fission and cyst formation
Examples: Amoeba, Entamoeba, etc.
3. Sporozoa or Sporozoans:
They are endoparasitic.
They don’t have any specialised organ for locomotion
The pellicle is present, which has subpellicular microtubules, that help in movement
Reproduction is by sporozoite formation
Examples: Plasmodium, Myxidium, Nosema, Globidium, etc.
4. Ciliophora or Ciliated protozoans:
See lessThey are aquatic and move actively with the help of thousands of cilia.
They have fixed shape due to covering of pellicle
They may have tentacles, e.g. in the sub-class Suctoria
Contractile vacuoles are present
Some species have an organ for defence called trichocysts
They move with the help of cilia and the movement of cilia also helps in taking food inside the gullet
They reproduce by transverse division and also form cysts
Examples: Paramecium, Vorticella, Balantidium, etc.