Notes, Exercises, Videos, Tests and Things to Remember on Sexual Cycle of Plasmodium
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When a mosquito bites a malaria-infected person, it sucks gametocytes along with blood. Gametocytes then reach to the stomach of mosquito where they become mature and undergo following developmental phases.
It is the process of formation of gametes from gametocytes. Micro gametocytes produce male gametes by the process of ex-flagellation. At the first nucleus of micro gametocytes divides into 6 to 8 nuclei. At the same time, an equal number of flagella like cytoplasmic extensions are also developed. Each of them carries single nucleus. Later they are separated from the main cytoplasmic body to welcome male gametes. They are active and motile. On the other hand, macro gametocyte is directly developed into female gamete after certain cytoplasmic reorganization. They are inactive and non-motile but contains reception cone.
It is the fusion of male and female gametes to produce a diploid zygote. Fertilization is anisogamous i.e. male and female gametes are dissimilar. Male gamete moves towards female gamete and enters inside through reception cone. Their cytoplasm and nucleus are fused to form a zygote.
At first, zygote remains rounded but later it becomes vermiform and motile. This worm-like motile zygote is called ookinete.
Ookinete starts to penetrate the inner wall of the stomach and gets encysted just below the outer basement membrane. This encysted zygote or ookinete is called oocyst. Up to 500 oocysts may be present in the stomach of infected mosquito which looks like blisters.
It is the process of formation of a large number of haploid sporozoites from the oocysts. Up to 10,000 sporozoites are produced from a single oocyst. At first, the nucleus of oocyst divides by meiosis and then by repeated mitosis. In this way, a large number of haploid nuclei are produced in growing oocysts. Each nucleus derives cytoplasm and develops into sporozoites. Inside mature oocyst, sporozoites are arranged around the vacuolated regions of cytoplasm. When mature oocyst burst sporozoites are released into haemo coelom from where they migrate towards salivary glands and become matured. In this way, the whole sexual cycle of plasmodium in the mosquito is completed within 10 days to 3 weeks.