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  Protozoa-Ciliophora, Biology tutorial

Protozoa-Ciliophora

General Characteristics of Protozoa-Ciliophora:

They are unicellular, animal-like cells with heterotrophic nutrition. There are said to be over 50,000 species. They are located anywhere water is present. They are generally free living with changeable methods of locomotion, few like Plasmodium are parasites. There are 3 phyla in the subkingdom, Ciliophora, Rhizopoda and Apicompleae. The protozoan paramecium is free living. You must recognize free living here as not parasitic. class ciliophora (ciliates) are enclosed with rows of minute, contractile protoplasmic cilia that are small editions of flagella. 2ndclass Rhyzopoda or Sarcodina has the bare undifferentiated surface. Third class sporozoa specialize in making spore to make sure infection to their host.

Protozoa are definitely animal in their feeding, attaining their nutrition from readymade sources comprising other animals. For their size, they can simply prey on others smaller than themselves. There are those which live on bacteria, others nourish on diatoms and small protozoans.

Structure of Paramecium - a typical Protozoan:

Paramecium lives in inactive or slow-flowing fresh water which has organic decaying matter. Structure of cell of Paramecium is complicated as it has to carry out all life activities. It has the characteristic shape - a blunt front part and the tapered back part. This form is preserved by presence of pellicle, the thin flexible outer region of cytoplasm. It is covered with cilia that happen in parts. Cilia are arranged diagonally round body. As beat to cause motion, body rotates as it moves forward. Between cilia are holes leading in chambers called trichocysts. Trichocysts release sharp fine threads that probable serve as anchor as animal feeds. There is apparent layer of ectoplasm in form of the gel. Basal bodies are situated here. They are structures from which cilia are produced. The network of fine fibre runs between basal bodies. These may serve for coordinating cilia as they beat. Bulk of cytoplasm is endoplasm that is in more liquid state than ectoplasm. Most of organelles are discovered in endoplasm. There is also oral grove at lower surface of organism near front. It tapers back in the narrow tube like gullet. At its end, endoplasm is open at the mouth-like cystosome. Oral grove and gullet are all lined with cilia that beat to waft in food particles in suspension. They go in food vacuoles formed in endoplasm. Undigested materials are sent through anal pore. There are 2 fixed contractile vacuoles in endoplasm for osmoregulation, as water constantly enters organism by osmosis as it lives in fresh water.

The contractile vacuole collects water from radiating canals frequently and sends them out to avoid animal from bursting. Cell has 2 nuclei - the beam-shaped polyploidy macronucleus. Polypoloid means it has more than 2 sets of chromosomes. It manages all other actions except reproduction. Small diploid micronucleus handles reproduction and formation of other micronuclei cell division. Paramecium reproduces sexually by conjugation and asexually by binary fission.

Adaptive Features of Paramecium:

List of structural characteristics and how they serve animal to live in the particular habitat.

A) For Movement in Water:

  • The slipper-like shape - tapering behind builds movement in water easy.
  • The spiral spin as cilia bit is the efficient means of movement - it spells development among minute organisms of the size.
  • The spiral arrangement of cilia.
  • Basal network of fine fibres (that reflect shape of animal) joined by corresponding row of basal granules.

B) For Feeding:

  • Oral groove and gullet lined with cilia
  • Bacteria present in water driven by ciliary action into gullet to anterior end where they are swallowed by pinocytosis
  • Digestive enzymes breakdown substance of bacteria in small organic molecules for building up its own type of living matter.
  • Egestion of undigested matter through the spot on cell surface.

C) For Osmoregulation:

Paramecium normally lives in the hypotonic environment that means that water diffuses from outside to inside of animal by osmosis. Paramecium eliminates water using active transport and has pair of organelles simply for this reason. These organelles are known as contractile vacuoles. When Paramecia are analyzed using light microscope contractile vacuoles(CV) can be observed as pair of spherical structures enclosed by the series of radiating ducts. Such ducts gathers water and pump it in innermost area by means of sets of contractile fibers. Consecutively, innermost sphere contracts when it is full, forcing water to outside of protist. 

D) For Reproduction:

Reproduction in paramecia is asexually, through binary fission. In reproduction, macronucleus splits by the kind of amitosis, and micronuclei undergo mitosis. Cell then splits transversally, and every new cell gets the copy of micronucleus and macronucleus.

Position of Protozoans in categorization Hierarchy of Living Things:

Earlier categorizations have put protozoans as first animals. Though, more modern ones have collected protozoans with others like plant-like, photosynthetic and aquatic algae, early fungi and slime moulds; into the phylum known as protoctista. This group appears to be link between prokaryotea (smallest group of organisms with cellular structure) and eukaryote plant and animals, generally multicellular).

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