Question

Trophozoites of plasmodium occur in
A. Liver cells
B. Spleen
C. Lymph channels
D. Red blood corpuscles

Answer 1

Hint:
Plasmodium is the causative agent of malaria. The agent species are Plasmodium falciparum, Plasmodium malariae, Plasmodium vivax, Plasmodium ovale and Plasmodium knowlesi.
Trophozoites are thick walled cysts formed by Plasmodium falciparum. They measure one-fifth the size of a human red blood cell. It is the most crucial stage of the Plasmodium life cycle.

Complete answer:
The Trophozoite stage of plasmodium is found on the surface of the red blood cells. It is the ring form.
When a female anopheles mosquito takes a blood meal from a malaria infected person, it takes along with the blood, the gametes of the causative agent. In the mosquito gut, these gametocytes undergo the sexual stage to form sporozoites. These sporozoites are stored in the salivary gland of the mosquito in the form of sporozoites. When the infected mosquito bites a healthy person, the sporozoites are passed on to the person. These sporozoites enter the circulation and reach the human liver and multiply to increase in number. The infected liver cell known as schizont bursts and releases the merozoite into blood circulation. These develop into trophozoites and reside on the membrane of the RBCs. The infected red blood cell ruptures to release the gametes into blood circulation.
So, the correct answer is option (D). Trophozoites of plasmodium occur in Red blood corpuscles.

Note:
 It takes upto 10 to 18 days for the parasite(plasmodium) to reach the mosquito's salivary gland from its gut. The symptoms of malaria occur after the bursting of RBCs infected with trophozoites. However, the mosquito vector does not suffer from the presence of the parasite.