Question

Identify the correct sequence of stages in the Ross cycle of plasmodium.
(A) Sporocyst
(B) Ookinete
(C) Sporozoites
(D) Zygote
(E) Oocyst

• A. C$\to$A$\to$E$\to$B$\to$D
• B. D$\to$E$\to$B$\to$A$\to$C
• C. D$\to$B$\to$E$\to$A$\to$C
• D. B$\to$D$\to$A$\to$E$\to$C

Answer 1

Answer: (C)

D$\to$B$\to$E$\to$A$\to$C

Ross cycle is the life cycle of Plasmodium in mosquito. Life cycle of Plasmodium involves two hosts:

Intermediate host, which is man and other primates

Definitive host, which is the female Anopheles mosquito.

When a female Anopheles mosquito bites a human, it infects his/her blood with the sporozoites of Plasmodium. The sporozoites reach liver and multiply asexually and are released in the blood which attack red blood cells. These are called merozoites which develop into schizont or trophozoites inside the RBCs which further divide to form merozoites. When the schizont is mature, RBCs burst and release merozoites into the blood. Some of merozoites in the blood, instead of developing into schizont, develop into immature sexual stages called gametocytes. When the female Anopheles mosquito bites a person, these gametocytes are sucked by it. The male and female gametocytes fertilise and develop in mosquito's stomach, forming a zygote. The zygote then becomes elongated and motile and is called ookinete which invade the midgut wall of the mosquito and develop into oocysts. The oocysts then develop into sporocysts and mature into infective stage called sporozoites. These sporozoites are then released in the human blood when the female Anopheles mosquito bites another human, and the cycle starts again.

Hence, the sequence of stages in Ross cycle of Plasmodium i.e. inside the female Anopheles Mosquito are:

Zygote → Ookinete → Oocyst → Sporocyst → Sporozoites

So, the correct answer is C.