Parasitism
Parasitism is a type of symbiotic relationship in which one organism (the parasite) lives in or on another
organism (the host) and benefits by obtaining nutrients or shelter, while the host is harmed.
Groups of parasitic protozoans
Parasitic protozoans are mainly classified into the following two major groups
Sarcodina (Amoeboid protozoans)
Sarcodina is a group of protozoans that move and feed using temporary finger-like projections called
pseudopodia (“false feet”). Most members are free-living, but some are parasitic and pathogenic to
humans.
General Characteristics of Sarcodina
Sarcodina are unicellular protozoans that move and capture food using pseudopodia (false feet). They
have no definite shape because their body is flexible. They are mainly heterotrophic and feed by
phagocytosis. Most Sarcodina live in freshwater, marine water, or moist environments, while some are
parasitic. They reproduce asexually, mainly by binary fission, and can form cysts to survive unfavorable
conditions.
Example :
Entamoeba histolytica
Entamoeba histolytica is a parasitic amoeboid protozoan belonging to the group Sarcodina. It lives
mainly in the human large intestine and is responsible for the disease called amoebic dysentery
(amoebiasis).
Structure of Entamoeba histolytica
Entamoeba histolytica is a unicellular parasitic protozoan with an irregular, constantly changing body
shape. It moves using pseudopodia (false feet). Its body is covered by a thin plasma membrane and the
cytoplasm is divided into ectoplasm (outer clear layer) and endoplasm (inner granular part). It has a single
nucleus that controls all cell activities. Food is taken in through pseudopodia and digested inside food
vacuoles present in the cytoplasm.
Life Cycle of Entamoeba histolytica
The life cycle of Entamoeba histolytica has two main stages:
The trophozoite stage and the cyst stage.
The trophozoite is the active, feeding form that lives in the human large intestine, where it multiplies by
binary fission and may cause tissue damage leading to amoebic dysentery. When conditions become
unfavorable, some trophozoites transform into cysts.
Parasitism is a type of symbiotic relationship in which one organism (the parasite) lives in or on another
organism (the host) and benefits by obtaining nutrients or shelter, while the host is harmed.
Groups of parasitic protozoans
Parasitic protozoans are mainly classified into the following two major groups
Sarcodina (Amoeboid protozoans)
Sarcodina is a group of protozoans that move and feed using temporary finger-like projections called
pseudopodia (“false feet”). Most members are free-living, but some are parasitic and pathogenic to
humans.
General Characteristics of Sarcodina
Sarcodina are unicellular protozoans that move and capture food using pseudopodia (false feet). They
have no definite shape because their body is flexible. They are mainly heterotrophic and feed by
phagocytosis. Most Sarcodina live in freshwater, marine water, or moist environments, while some are
parasitic. They reproduce asexually, mainly by binary fission, and can form cysts to survive unfavorable
conditions.
Example :
Entamoeba histolytica
Entamoeba histolytica is a parasitic amoeboid protozoan belonging to the group Sarcodina. It lives
mainly in the human large intestine and is responsible for the disease called amoebic dysentery
(amoebiasis).
Structure of Entamoeba histolytica
Entamoeba histolytica is a unicellular parasitic protozoan with an irregular, constantly changing body
shape. It moves using pseudopodia (false feet). Its body is covered by a thin plasma membrane and the
cytoplasm is divided into ectoplasm (outer clear layer) and endoplasm (inner granular part). It has a single
nucleus that controls all cell activities. Food is taken in through pseudopodia and digested inside food
vacuoles present in the cytoplasm.
Life Cycle of Entamoeba histolytica
The life cycle of Entamoeba histolytica has two main stages:
The trophozoite stage and the cyst stage.
The trophozoite is the active, feeding form that lives in the human large intestine, where it multiplies by
binary fission and may cause tissue damage leading to amoebic dysentery. When conditions become
unfavorable, some trophozoites transform into cysts.
