14.) Elaborate the life cycle of one protists who starts life in a mosquito and matures in humans with a colorful diagram. 

A.) 

Plasmodium vivax

Plasmodium vivax is a protozoan causing malaria. It is a parasite. It is carried by female Anopheles mosquitoes to humans. Different species of Plasmodium cause different types of malaria.

Plasmodium is a unicellular eukaryotic organism. It is a sporozoan and has a spore-like infectious stage in its life cycle. It completes its life cycle in two hosts, i.e. humans and female Anopheles mosquitoes.

Plasmodium Life Cycle

Plasmodium vivax completes its life cycle in two hosts. The sexual phase of the life cycle occurs in insects and asexual reproduction occurs in humans. The female Anopheles mosquito also acts as a vector or transmitting agent.

Asexual Stage

Sporozoite is the asexual stage of the Plasmodium. It is the infectious stage that infects humans. Sporozoites get transmitted from the female Anopheles to humans when the infected mosquito bites. The sporozoites reach the human liver cells and mature into schizonts. The cells burst and it releases merozoites into the blood. The initial multiplication in the liver is called exo-erythrocytic schizogony. In Plasmodium vivax, a dormant stage may persist for weeks to even years, if remain untreated. It is known as hypnozoites.

Merozoites attack RBCs and multiply asexually leading to the rupture of RBCs. The asexual multiplication in the erythrocytes is known as erythrocytic schizogony. The merozoites change into the ring-stage immature trophozoites, which mature into schizonts. Schizoints rupture and release merozoites. They release a toxic substance known as haemozoin. Haemozoin is responsible for recurring chills and high fever during malaria.

See more: MCQs on Vector-borne Diseases

Sexual Stage

The male and female gametocytes are produced in the RBCs of humans. Some of the trophozoites in erythrocytes differentiate into gametocytes, which is the sexual stage. It forms microgametocytes (male) and megagametocytes (female).

When a female Anopheles mosquito bites an infected human, it takes up the gametocytes with blood. Further fertilisation and development take place in the gut of the female mosquitoes. The multiplication in mosquitoes is known as the sporogonic cycle.

The male gametocytes penetrate the female gametocytes leading to the formation of zygotes in the stomach of mosquitoes. Zygotes develop into ookinetes as they become motile and elongated. Ookinetes enter the midgut wall and develop into oocysts. Oocysts rupture and release sporozoites, which is the infective stage for humans.

The sporozoites migrate to salivary glands and are stored there. When an infected mosquito bites a human, these sporozoites enter the human blood and the cycle continues.

Life Cycle Diagram