Reference Notes | Zoology
Plasmodium – Asexual and Sexual Reproduction Cycle in Man
For: Science Class 11 (Biology)
It is a kind of protozoa, which causes malaria. A French microbiologist Charles Laveran in 1880 discovers plasmodium in the blood of patient suffering form Malaria. In RBC, he found a cell which is amoeba like and this structure was not found in healthy man. Then he injected the blood of patient to the healthy man them the healthy man suffered from fever soon.
There are four species of malarial parasites.
Plasmodium vivax: It produces fever at every 48 hours. This is mostly found in India and Nepal.
Plasmodium malariae: It produces fever at every 72 hours.
Plasmodium falciperum: It produces continuous fever with high temperature
Plasmodium ovalae: It produces night fever.
Reproduction (Life Cycle)
Asexual Cycle in Man
- When an anopheles mosquito bites a man to suck blood, she injects saliva-containing sporozoites. The sporozoites are unicellular, uninucleate, and spherical and slightly curved stage of the Plasmodium.
- The sporozoites after inoculation into the body circulate for about ½ an hour in the blood and reach to the liver.
- There in liver the sporozoites start to penetrate the liver cells. Within the liver cell they become large and spherical in shape. This structure is called as Schizont. The Schizont undergoes multiple divisions to produce many spindle shaped structure called merozoites or cryptozoites. The process upto the formation of cryptozoites is called Pre Erythrocytic Schyzogony.
- Now cryptozoite infects the new liver cells and penetrate into the cells. Within the cell, it becomes large and spherical in shape and called as schizont. The schizont undergoes multiple binary fission to produce many spindle shape structures called Metacryptozoites. Some metacryptozoites again infect the new liver cells and repeat the same cycle.The process from infection of new liver cell to the cormation of metacryptozoites is termed as Exo-Erythrocytic Schizogony.
- But some metacryptozoites divide and form two types of cryptozoites, one type of cryptozoites are larger and called macrometacryptozoites and another are smaller called as micrometacryptozoites.
- Now micrometacryptozoites infect the RBC within the RBC it becomes large and spherical in shape. This structure is called trophoizoite. Within trophozoites large vacuole is formed and nucleus of its move at a side. This stage is called signet ring stage. Now vacuole breaks into small vacuole and the nucleus appear at centre and shape of the cell becomes like amoeba. This stage in RBC of the parasite is called amoeboid trophozoites.
- In amoeboid trophozoite stage, haemoglobin of RBC is broken into haematin and protein. The protein is used by cell and hematin gets converted into haemozoin which is toxic. At this stage in the cytoplasm of RBC, small granules are present and called as Schuffner’s Granules.
- Now the amoeba like trophozoite becomes spherical. This is called schizont or mature trophozoite.
- Now the schozont again divides to produces many spindle shaped micromerozoites. This cycle is called Erythrocytic Schizogony.
- Some micromerozoites again infect the RBC and new liver cells and repeat the same cycle. This cycle is called Post Erythrocytic Schizogony.
Sexual Cycle in Man
But some of the micromerozoites infect the RBC but do not repeat the same cycle. The micromerozoites having nucleus at the centre is called microgametocyte and those having nucleus at a side is called macrogametocyte. Now when mosquito bites man both the gametocytes are sucked through the blood and they reach to the stomach of the mosquito.