Question

microbiology

Protozoa are a polyphyletic group .What does that term mean?What common characteristics do Protozoa have that facilitates informally grouping them together?There are four pathogenic protozoan groups, based on their method of motility.Briefly describe these groups, give an example of a common parasite within each group, the disease they cause and their reservoirs / source. minimum 150 words.

Answer 1

Polyphyletic group means group of organisms derived from common evolutionary ancestor but does not suitable for placing them in the same taxon. Simply their members come from multiple ancestral sources regardless of showing same characteristics.

Except ciliates ( ciliophora) other sub-classes of protozoans are polyphyletic group.

Protozoans are single celled eukaryotes placed under kingdom Protista. They are heterotrophs and feeds on organic matter like microbes or other organic tissues of debris. They live as parasites or predators .

As they show motility, predation but lack of cell wall, they are believed to be have primitive relation with animals. Thus they are also called as " one - celled animals ".

Because of the presence of above characteristics, they are placed together in kingdom Protista.

Classification of Protozoans:

On the basis of their motility, they are placed under four major groups which are as follows:

1) Amoebaoid protozoans ( sarcodina): oranisms in this group have pseudopodia for locomotion and capturing of food. They live in either fresh water , sea water or moist soil. Organisms living in marine water forms silica cell on their surface. They reproduce asexually by fission, budding or spores and sexually through syngamy. They have holozoic mode of nutrition.

Example: Entamoeba histolytica. They predominantly infect humans and other primates and causes amoebiasis. They are anaerobic parasite found in the human colon.

2) Flagellated protozoans (mastigophora) : organisms placed in this group have whiplike organelle called "flagella" as their locomotory organ. They are either free- living or parasite.

Example: Trypanosoma brucei gambiense. They causes African sleeping sickness in humans and transmitted by tsetse fly. Person experienced fever muscle and joint pain and inflammation in lymph nodes.

3) Ciliated protozoans ( ciliophora): large number of hair like organs called " cilia" are the locomotory organ in this group of organisms. They are aquatic and have gullet opening to the outside of the cell surface. Rows of cilia moves in a coordinated manner and causes water laden with food steered into the gullet.

Example: Balantidium coli. only known ciliated protozoans to infect humans. They cause disease balantidiasis which is a zoonotic disease. They live in the cecum and colon of human, pig, rats and other mammals. Infection occurs when the cysts are ingested through contaminated food and water.

4) Sporozoans: They are sopre producing cells and their adults usually lacks organs of motility.

Example: Plasmodium falciparum. Causative agent of malaria. Transmitted through female anopheles mosquitoes. Infective dtage called sporozoites are released from the salivary gland of mosquitoes. When mosquitoes bite humans , introduced in their blood stream. They usually multiply within the liver cell of the humans and then attack RBCs, resulting in their rupture. Ruptured RBC released toxic substance called haemozoin responsible for chill and high fever.