Q.2 Write short notes on the following.
(a)Osmoregulation in Protozoa. (2009)
(b) Leishmania, or structure of leishmania. (2005, 06, 07, 08, 13)
Ans. (a) Osmoregulation in Protozoa: -
Protozoa living in fresh water are subjected to a hypotonic environment. Water flows across their plasma membrane since their cytosol is always hypertonic to the environment. Many wall-less protozoa have an organelle, the contractile vacuole complex (CVC), that collects and expels excess water. Recent progress shows that most, if not all, CVCs are composed of a two-compartment system encircled by two differentiated membranes. One membrane, which is often divided into numerous vesicles and tubules, contains many proton-translocating V-ATPase enzymes that provide an electrochemical gradient of protons and which fuses only with the membrane of the second compartment. The membrane of the second compartment lacks V-ATPase holoenzymes, expands into a reservoir for fluid storage, and is capable of fusing with the plasma membrane. It is this second compartment that periodically undergoes rounding (“contraction”), setting the stage for fluid expulsion. Rounding is accompanied by increased membrane tension.
In amoeba the function of contractile vacuole is
· Excretion and · Osmoregulation
The water content in the organism has to be regulated as there is a constant inflow of excess water. This is because the cell membrane surrounding the animal is semipermeable and as the protoplasm contains a higher concentration of salts than the water outside, water enters the cell by osmosis. This water is more than what is actually required by the animal. To counter this, excess water collects into the contractile vacuole as fast as it enters the body. The vacuole slowly grows larger until it reaches the maximum size. Then the endoplasm in the area surrounding the vacuole contracts and the fluid contents which contain traces of urea and carbon dioxide are discharged out into the surrounding pond water. Thus the contractile vacuole functions effectively as an organelle that performs both excretion and osmoregualtion.
Since ciliates (and many freshwater protozoans) are hypotonic, removal of water crossing the cell membrane by osmosis is a significant problem. One commonly employed mechanism is a contractile vacuole. Water is collected into the central ring of the vacuole and actively transported from the cell.
Osmoregulation in Paramecium
(b) Leishmania: -
Structure of Leishmania: -
Leishmania is a genus of trypanosome protozoa, and is the parasite responsible for the disease leishmaniasis.
It is spread through sandflies of the genus Phlebotomus in the Old World, and of the genus Lutzomyia in the New World. Their primary hosts are vertebrates; Leishmania commonly infects hyraxes, canids, rodents, and humans.
Leishmania cells have two morphological forms: promastigote (with an anterior flagellum) in the insect host, and amastigote (without flagella) in the vertebrate host. Infections are regarded as cutaneous, mucocutaneous, or visceral.
Cutaneous (localized and diffuse) infections appear as obvious skin reactions. The most common is the Oriental Sore Visceral infections are often recognized by fever, swelling of the liver and spleen, and anemia. They are known by many local names, of which the most common is probably Kala azar, and are caused exclusively by species of the L. donovani complex (L. donovani, L. infantum syn. L. chagasi.
In a vertebrate body the organism occurs in the phagocytotic cells as sound or oral amastigote parasites. Each of them measures 2-5 m in length and contains a blepharoplast and a kinetoplast. The flagellum is reduced to a ting fibril within the cytoplasm. In the invertebrate host (insect) the parasite occurs in the mid gut as the promastigote (leptomonad) form which is elongated with a large nucleus and a short free flagellum arising from a blepharoplast located near the anterior end of the body.
Life Cycle: -
Description: -
Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies. The sandflies inject the infective stage (i.e., promastigotes) from their proboscis during blood meals
(1) Promastigotes that reach the puncture wound are phagocytized by macrophages
(2) And other types of mononuclear phagocytic cells. Progmastigotes transform in these cells into the tissue stage of the parasite (i.e., amastigotes)
(3) Which multiply by simple division and proceed to infect other mononuclear phagocytic cells
(4) Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sandflies become infected by ingesting infected cells during blood meals.
(5) In sandflies, amastigotes transform into promastigotes, develop in the gut
(6) (In the hindgut for leishmanial organisms in the Viannia subgenus; in the midgut for organisms in the Leishmania subgenus), and migrate to the proboscis.
Q.3 Give an account of various disease causing protozoa in human beings. (2005, 09)
Related Questions -
Q. Enumerate various disease caused by protozoa in man. (2011)
Q. Write an essay on “protozoa and human diseases.” (2014)
Q. Write short note on Amoebiasis. (2018, 19)
Q. Write short note on Leishmania. (2019)
Ans. Disease Causing Protozoans: -
(1) ENTAMOEBA HISOLYTICA: -
It causes amoebiasis or amoebic dysentry. Its trophozoites that penetrate the wall of the intestine (colon), secrete histolytic enzymes and feed upon its cells causing the formation of ulcers. These ulcers rupture and discharge blood and mucus into the intestine that pass with stools.
No intermediate host is involved in the life cycle of the parasite. Transmission of the parasite from man to man takes place through tetra nucleate cyst. Prior to cyst formation the trophozoite changes into a smaller minuta form a tetranucleate cyst. These cysts are voided with the faecal matter and contaminate food and water and spread into new hosts – houseflies help in its rapid spread.
(2) GIARDIA: -
Giardia intestinalis causes diarrhoea which is characterized by loose bowels. It is a flagellate parasite which harbours the small intestine. Its cell body is pear shaped with dorsal side convex and ventral side flattened. It bears two nuclei and four pairs of flagella arranged symmetrically.
The parasite divides by binary fission to multiply rapidly and feeds upon amino acids and vitamins contained in the food within the intestine. This causes intestinal disorders.
Transmission of the parasite takes place through cysts which are voided with the new hosts in food or water. The infection of giardia is more in children than in adults.
(3) TRYPANOSOMA: -
It causes trypanosomiasis which are flagellate parasites of the blood and gut. Sleeping sickness is a dangerous disease of man in tropical africa. Its causative agent is T.gambiense and is transmitted by a tse tse fly, glossinia palpalis. Infestation of the lymph system leads to glandular swelling which is a prominent feature of sleeping sickness. Later the parasites penetrate into the cerebrospinal fluid causing damage to the brain and bring about the lethargy characteristic of sleeping sickness.
T.cruzi is the causative agent of american trypanosomiasis or chaga‘s disease. It is transmitted by bugs of the genus Triatoma. Transmission to man is not due to bug bite but through its faeces.
(4) LEISHMANIA: -
It causes leismaniasis. It is also a parasitic flagellate that inhabit phagocytic cells in body organs in vertebrates and gut in insect hosts. Leishmania donovani is the causative agent of kala azar or visceral leishmaniasis . A major characteristic of this disease is a considerable enlargement of the spleen due to blockage of reticuloendothelial system by parasites.
L.tropica is the causative agent of skin leishmaniasis (oriental sore). The infection is restricted to the endothelium of skin capillaries and leads to lump like boils.
L.brasiliensis causes a disease called espundis, producing multiple sores over large areas of the body. Development of ulceration in nasal cavities, mouth and pharynx is quite frequent.
Leishmania species are transmitted from man to man by bites of sandflies belonging to the genus phlebotomus.
(5) TRICHOMONAS: -
It causes trichomoniasis. It is a flagellate protozoan. Its body is rounded with one nucleus, an axostyle, a parabasal body, and 4-6 flagella. The most common pathogenic species is trichomonas vaginalis that inhabits the vagina of woman and causes vaginitis. The disease is characterized by inflammation, burning sensation and frothy vaginal discharge. The transmission is always through sexual intercourse by male members who act as intermediaries.
(6) PLASMODIUM: -
It causes malaria. It is transmitted through the bite of female anophles mosquito. In man tha parasite attacks the liver cells and the red blood cells. A toxic substance the haemozoin released by the parasite causes malaria.
Malaria is characterized by the periodic attacks of fever. The fever is repeated in the tertain malaria caused by P.vivax every third day, in ovale malaria caused by P.ovale every third day, in quartan malaria caused by p.malariae every fourth day and in malignant tertian malaria caused by P.falciparum every third day.
(7) TOXOPLASMA: -
It causes toxoplasmosis which is caused by Toxoplasma gondii a sporozoan parasite. The parasite occupies the cells of the reticuloendothelial and central nervous system. The parasites multiply by endodyogeny but under certain conditions large cysts are also produced.
(8) BALANTIDIUM COLI: -
It is an intestinal ciliate. It cause balantidial dysentry which is characterized by diarrhoea and ulceration of the large intestine. The transmission of the parasite to a new host takes place through cysts in contaminated food or water.
