Question

The Plasmodium reproduces in the human liver by _______ and in human blood by ______.
A. Sexual reproduction, Asexual reproduction
B. Asexual reproduction, Asexual reproduction
C. Spore formation, Sexual reproduction
D. Sexual reproduction, Asexual reproduction

Answer 1

Hint: Plasmodium protozoans are transferred by the Anopheles mosquito as a definitive phase so reproduction occurs in the mosquito, thus, the processes occurring in the human body involve reproduction both in the liver and in red blood cells.

Step by step answer:When a female Anopheles mosquito which is infected with the Plasmodium parasite bites a human and sucks blood, it will inject sporozoite form of the parasite into human blood. A varying number of sporozoites may enter the blood at one time ranging from tens to hundreds. Some of these sporozoites will be eaten and destroyed by phagocytes while a few escape and reach the liver where the exo-erythrocytic cycle takes place. Inside the liver, spindle-shaped sporozoites become rounded, increase in size, and divide by asexual reproduction to form daughter cells called schizonts. As the schizonts in the liver mature, they destroy the liver cells called hepatocytes. Soon after, schizonts rupture and release merozoites in the blood which invaginate or penetrate into the red blood cells, and the erythrocytic stage begins. Now, the merozoites are in the blood, in red cells where they undergo another asexual reproduction phase leading to the formation of the trophozoite form of the parasite which later develops into schizonts. The schizonts on maturing rupture or burst and release merozoites in blood. The bursting schizonts lead to the release of pyrogens which are responsible for the fever and chills occurring during malaria. The merozoites are released by destroying red cells and the released merozoites infect new RBCs.
Hence, the correct option is B.
Additional information: Some merozoites form male and female gametocytes in the blood which can be taken up by Anopheles mosquito where the male and female gamete develop from gametocytes, fuse and sexual reproduction occur. After fertilization, zygote forms that travel through the midgut of the mosquito to the salivary glands and form sporozoites there which can enter another human blood on a bite of such a mosquito. Plasmodium while in the RBCs feeds on Haemoglobin pigment present in the red cells but does not metabolize it and so converts it into another product called haemozoin. As the RBCs rupture, it leads to the release of haemozoin pigment which leads to the activation of Immunity.

Note: Human is an intermediate host of Plasmodium and so no sexual phase will occur in the intermediate host. The sexual phase occurs only in the definitive host of the parasite. The characteristic paroxysmal fever in malaria occurs due to the rupture of RBCs. As the RBCs rupture, one phase of fever occurs which subsides soon and after a while, the merozoites infect new RBCs and destroy those which lead to another period of fever.