Test: Entamoeba (Old NCERT) - NEET MCQ

There are three stages in the life cycle of the Amoeba, trophozoite, pre-cystic and the cystic stage. Tetranucleate cysts are eliminated in the faeces of the infected person. Infection with Entamoeba histolytica is acquired by indirect fecal-oral route or by sexual intercourse. The water or food which is contaminated with faeces is responsible for the entry of the cyst in the healthy individual. This cyst is the infective stage in the humans.

As per the  International Rules of Nomenclature, the scientific name consists of two parts, genus and species. Both genus and species are either italicized or are underlined. In genus, the first letter is capital whereas species name is always written in lower case letters. Musca domestica is the common house fly. In option A, the scientific name is not italicized. Plasmodium falciparum is a protozoan pathogen causing the most serious type of malaria. Felis tigris is the scientific name of Indian tiger. In option C, the first letter of genus Felis is not written in capital letter. Escherichia coli is the full name of E. coli. It commonly occurs in the human intestine.
Thus, the correct answer is option B.

Contractile vacuoles, common in freshwater Protozoa, eliminate water that moves into the cells by osmosis. The contractile vacuole is present in amoeba but absent in Entamoeba because Amoeba lives in water and needs osmotic regulation. The contractile vacuole is basically a water bubble within the endoplasm of A. proteus. Its function is to regulate the water content of the cell. It is also a means of excreting its waste from the cell (out through the cell membrane) via diffusion. E. histolytica doesn't need to have a contractile vacuole as it lives in an isotonic environment. Since the osmotic concentration of its body remains equal to its surroundings entry of water through osmosis will not happen. Therefore, there is no need of contractile vacuole.

Minuta is a type of cysts, in this body gets smaller, food vacuole remains absent, non- motile form, non- feeding form and it is a non- pathogenic form.

Minuta is the pre-cystic form which is smaller, spherical, non-feeding, non-motile and non-pathogenic. It measures to about 7-10 microns in diameter and resembles the trophozoite form in its structure except that it is smaller in size having no pseudopodium and contractile vacuole.

The active trophozoite (growing stage in the life cycle of some protozoan parasites when they are absorbing nutrients from the host) of E. histolytica ranges in size from 20- 30 μm. It is the most active, motile and feeding form which is pathogenic to man. It resembles the common amoeba in all the structural details.

Entamoeba histolytica is an anaerobic parasitic protozoan, part of the genus Entamoeba. Predominantly infecting humans and other primates, E. histolytica is estimated to infect about 50 million people worldwide. Previously, it was thought that 10% of the world population was infected, but these figures predate the recognition that at least 90% of these infections were due to a second species, E. dispar. Mammals such as dogs and cats can become infected transiently, but are not thought to contribute significantly to transmission.
The housefly, Musca domestica, is a fly of the suborder Cyclorrhapha. It is the most common of all domestic flies, accounting for about 91% of all flies in human habitations. 
Amoeba proteus, is an Amoeba closely related to the giant amoebae and a species commonly bought at science supply stores.
Hydra oligactis, also known as the brown Hydra, is a species of hydra found widely dispersed in the northern temperate zone. It is a common organism found in still waters from early Spring to late Autumn.

Amebiasis is a disease caused by infection with a parasitic amoeba that, when symptomatic, can cause dysentery and invasive extraintestinal problems. The cause of amebiasis is mainly the protozoan parasite Entamoeba histolytica.

Entamoeba histolytica is a monogenetic parasite, as it's life cycle is completed in a single host that is man. All other options are digenetic parasites, as they complete their life cycle in two hosts
So, the correct answer is 'Entamoeba histolytica'.

Entamoeba histolytica is a protozoan parasite that infects humans and causes the disease called amebiasis. And the spectrum of intestinal amebiasis varies from colonization without showing any symptoms to fulminating diarrhea and intestinal hemorrhage.

The adult trophic form of Entamoeba is known as 'Trophozoite' or 'Magna'. It inhabits anterior part of large intestine, i.e., colon of human beings.It leads a parasitic life and resembles amoeba. Its body is covered by plasmalemma and cytoplasm is differentiated into ectoplasm and endoplasm. There is a single large, broad and blunt pseudopodium formed of ectoplasm. Endoplasm contains single spherical nucleus and food vacuoles. Nucleus has a peripheral crown of chromatin blocks and a centrally located nucleolus. Entamoeba lacks contractile vacuole. Thus, the correct answer is option A.

A contractile vacuole expands and contracts. It pumps out the water from the cell through a process called osmoregulation. 
Fresh water is a hypotonic solution, osmosis will continually transfer water into the amoeba. Without a way to counteract this, the amoeba will swell to the point it bursts. To that extent, freshwater species have developed contractile vacuoles. 

Contractile vacuoles, common in freshwater Protozoa, eliminate water that moves into the cells by osmosis. The contractile vacuole is absent in Entamoeba. Its function is to regulate the water content of the cell. It is also a means of excreting its waste from the cell (out through the cell membrane) via diffusion. E. histolytica doesn't need to have a contractile vacuole as it lives in an isotonic environment. Since the osmotic concentration of its body remains equal to its surroundings entry of water through osmosis will not happen. Therefore, there is no need of contractile vacuole. Thus, the correct answer is A.

The organism has a simple life cycle, existing as either the motile trophozoite or the infectious, hardy cyst form. Trophozoites of E. histolytica reside within the anaerobic confines of the human colon, lack mitochondria, derive energy from fermentation and reproduce by binary fission.
Hence, the correct answer id Option B.

Life Cycle (Entamoeba gingivalis): There is no known cyst stage for Entamoeba gingivalis; trophozoites live in the oral cavity of humans, residing in the gingival pockets near the base of the teeth. They are not considered pathogenic, and feed on bacteria and other debris.

Entamoeba histolytica is a protozoan protist. It is pathogenic in nature. It resides in the upper part of the human large intestine and causes the disease known as amoebic dysentery or amoebiasis. The symptoms of the disease are abdominal pain, repeated motions with blood and mucus. Entamoeba histolytica is transmitted through food or water contaminated with cysts. A mature cyst is called quadri-nucleate cyst. It has four nuclei and two chromatid bodies. Quadrinucleate cyst is the infective stage.

Entamoeba histolytica is an anaerobic parasitic amoebozoan, part of the genus Entamoeba. The active (trophozoite) stage exists only in the host and in fresh loose feces; cysts survive outside the host in water, in soils, and on foods, especially under moist conditions on the latter. The infection can occur when a person puts anything into their mouth that has touched the feces of a person who is infected with E. histolytica, swallows something, such as water or food, that is contaminated with E. histolytica, or swallows E. histolytica cysts (eggs) picked up from contaminated surfaces or fingers. The cysts are readily killed by heat and by freezing temperatures, and survive for only a few months outside of the host. When cysts are swallowed they cause infections by excysting (releasing the trophozoite stage) in the digestive tract.

There is no known cyst stage for Entamoeba gingivalis; trophozoites live in the oral cavity of humans, residing in the gingival pockets near the base of the teeth. They are not considered pathogenic, and feed on bacteria and other debris.

Cysts of E. histolytica contains one to four nuclei. Chromatoid bodies are usually present in young cysts as elongated bars with bluntly rounded ends. Glycogen is usually diffuse, but in young cysts it is often present as a concentrated mass, staining reddish brown with iodine.

The adult trophic form of Entamoeba is known as 'Trophozoite' or 'Magna'. It inhabits anterior part of large intestine, i.e., colon of human beings.It leads a parasitic life and resembles amoeba. Its body is covered by plasmalemma and cytoplasm is differentiated into ectoplasm and endoplasm. There is a single large, broad and blunt pseudopodium formed of ectoplasm. Endoplasm contains single spherical nucleus and food vacuoles. Nucleus has a peripheral crown of chromatin blocks and a centrally located nucleolus. Entamoeba lacks contractile vacuole. Thus, the correct answer is option D.

Infection by Entamoeba histolytica occurs by ingestion of mature cysts in fecally contaminated food, water, or hands.Transmission can also occur through exposure to fecal matter during sexual contact Housefly (in which case not only cysts, but also trophozoites could prove infective).

Entamoeba histolytica is a protozoan parasite responsible for a disease called amoebiasis. It occurs usually in the large intestine and causes internal inflammation. The life cycle of Entamoeba histolytica does not require any intermediate host. Mature cysts (spherical, 1215 m in diameter) are passed in the feces of an infected human. Another human can get infected by ingesting them in fecally contaminated water, food or hands. If the cysts survive the acidic stomach, they transform back into trophozoites in the small intestine. Trophozoites migrate to the large intestine, where they live and multiply by binary fission. Both cysts and trophozoites are sometimes present in the feces. Cysts are usually found in firm stool, whereas trophozoites are found in loose stool. Only cysts can survive longer periods (up to many weeks outside the host) and infect other humans. If trophozoites are ingested, they are killed by the gastric acid of the stomach. Occasionally trophozoites might be transmitted during sexual intercourse. Damage is caused by the lysis of epithelial cells, due in part to the insertion of pore-forming proteins into the membrane of the cell. Neutrophils and non-activated macrophages may also be killed and ingested by the organism, limiting the ability of the immune system to deal with the disease. E. histolytica is also capable of phagocytosing red blood cells. They feed up on erythrocytes, mucosa and submucosa of colon.

Entamoeba coli is a non-pathogenic species of Entamoeba that frequently exists as a commensal parasite in the human gastrointestinal tract.

Entamoeba histolytica is an anaerobic parasitic protozoan that infects the digestive tract of predominantly humans and other primates. Transmission of the parasite occurs when a person ingests food/water that has been contaminated with infected feces. The infection E. histolytica is called Amebiasis (or Amoebiasis).

Cysts of Entamoeba coli are usually spherical but may be elongated and measure 10–35 µm. Mature cysts typically have 8 nuclei but may have as many as 16 or more. Entamoeba coli is the only Entamoeba species found in humans that has more than four nuclei in the cyst stage.

Entamoeba gingivalis is found in 95% of people with gum disease and rarely in people with healthy gums. Cyst formation is not present; therefore transmission is direct from one person to another by kissing, or by sharing eating utensils.

E. histolytica usually resides in the large intestine, and can persist there for months or years and cause an asymptomatic intestinal infection.

Chromatoid bodies have cytoplasm with a single nucleus, rarely up to four; often with ingested red blood cells, sometimes with leukocytes, or bacteria; rich in glycogen; with ribosomes arranged in helices which aggregate to form characteristically shaped elongate bars with rounded ends.