| Malaria is an infectious disease caused by a one-celled parasite known as Plasmodium. The parasite is transmitted to humans by the bite of the female Anopheles mosquito. The Plasmodium parasite spends its life cycle partly in humans and partly in mosquitoes. (A) Mosquito infected with the malaria parasite bites human, passing cells called sporozoites into the human’s bloodstream. (B) Sporozoites travel to the liver. Each sporozoite undergoes asexual reproduction, in which its nucleus splits to form two new cells, called merozoites. (C) Merozoites enter the bloodstream and infect red blood cells. (D) In red blood cells, merozoites grow and divide to produce more merozoites, eventually causing the red blood cells to rupture. Some of the newly released merozoites go on to infect other red blood cells. (E) Some merozoites develop into sex cells known as male and female gametocytes. (F) Another mosquito bites the infected human, ingesting the gametocytes. (G) In the mosquito’s stomach, the gametocytes mature. Male and female gametocytes undergo sexual reproduction, uniting to form a zygote. The zygote multiplies to form sporozoites, which travel to the mosquito’s salivary glands. (H) If this mosquito bites another human, the cycle begins again. |
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