Where can sporozoites of the malarial parasite be found?

The correct answer is Option (4) → Saliva of an infected female Anopheles mosquito

Malaria is caused by the protozoan Plasmodium, which needs two hosts, human and mosquito. Sporozoites are the infectious form. They are formed inside a female Anopheles mosquito after it has sucked the blood of an infected person. They collect in the mosquito’s salivary glands and enter a human with the saliva when the mosquito bites. In the human, the parasites first multiply in liver cells and then attack red blood cells.

Option (1) Red blood cells (RBCs) of humans suffering from malaria — Incorrect. Inside red blood cells the parasites multiply and burst the cells, and the sexual stages (gametocytes) develop there. These are not sporozoites.

Option (2) The spleen of an infected person — Incorrect. The sporozoites travel through the blood to the liver, not to the spleen. The spleen has no place in the life cycle of Plasmodium given in the book.

Option (3) Salivary glands of newly moulted female Anopheles mosquitoes — Incorrect. Sporozoites form only in a mosquito that has taken in gametocytes from an infected person. A newly moulted mosquito has not yet had any blood meal, so its salivary glands hold no sporozoites.

Option (4) Saliva of an infected female Anopheles mosquito — Correct. The salivary glands of an infected female Anopheles store the sporozoites, and they pass into the human with the saliva at the bite.

NCERT Extract:
Common Diseases in Humans – “… Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. … When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development. The parasites multiply within them to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into his/ her body, thereby initiating the events mentioned above.”

Figure 7.1 Stages in the life cycle of Plasmodium