Question

Which state of Plasmodium is infective for mosquitoes?
a) Sporozoite
b) Ookinete
c) Trophozite
d) Gametocyte

Answer 1

In certain Apicomplexans, the repeated division of the oocyst during the process of
sporogony results in the formation of small, elongated cells. These cells are then taken up by the mosquitoes. Hence, they get infected by them. These are motile i.e. they are capable of movement.
Complete answer:
Plasmodium is a parasitic protozoan that causes malaria. It is transmitted by mosquitoes, particularly female Anopheles. These mosquitoes act as a transmitting agent from an infected host to a healthy one. They themselves, however, are the carriers. They are primary hosts for the protozoan. Sporozoites are formed in the gut of the mosquito. The life cycle of plasmodium begins when an infected anopheles mosquito bites a healthy human which then becomes the secondary host. The sporozoites travel inside the blood vessels and reach the liver cells, called hepatic cells, where they reproduce asexually. This
results in the production of merozoites which multiply further in what is called blood schizogony, producing multiple merozoites that develop into gametocytes. When an uninfected mosquito takes a blood meal these gametocytes, both male and female, fertilize each other within the gut of the mosquito forming ookinete. The ookinetes mature into sporozoites which are stored in the salivary glands and the cycle repeats itself when the mosquito bites another healthy human.
Thus, the correct option is (D).

Note: The infective stage is known as sporozoites discharged from the secretion glands through the proboscis of the dipteron and enters the blood throughout the feeding. Thousands of Plasmodium parasites produced within the infected mosquitoes are transferred into the human blood with one bite. At this stage, the parasites are within the sporozoan stage, where they exist as tiny elongated cells.