83. Which one of the following life cycle stages of Plasmodium falciparum is infectious?
(A) Sporozoite
(B) Cryptozoite
(C) Merozoite
(D) Trophozoite
The infectious stage of Plasmodium falciparum, the deadliest malaria parasite, is the sporozoite, transmitted by Anopheles mosquitoes. This multiple-choice question tests understanding of malaria transmission basics in biology exams. Correct answer: (A) Sporozoite.
Correct Answer and Explanation
Sporozoites represent the infective form of Plasmodium falciparum for humans, injected into the bloodstream via a mosquito bite during feeding. These motile parasites travel to the liver, initiating infection without causing symptoms at this stage. Only sporozoites from the mosquito’s salivary glands can establish primary human infection.
All Options Analyzed
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(A) Sporozoite: Correct. This banana-shaped stage develops in mosquito salivary glands and infects human hepatocytes upon injection, marking the start of the exo-erythrocytic cycle.
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(B) Cryptozoite: Incorrect; this term is outdated or refers to dormant hypnozoites in P. vivax or P. ovale, not present in P. falciparum and not infectious to new hosts.
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(C) Merozoite: Incorrect. Merozoites emerge from liver schizonts or erythrocyte schizogony to invade red blood cells, perpetuating blood-stage infection but not transmitted between hosts.
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(D) Trophozoite: Incorrect. This feeding stage develops inside erythrocytes from merozoites, causing malaria symptoms via hemoglobin digestion, but remains intracellular and non-infectious.
