Plasmodium is a protozoan parasite that causes malaria in humans. The life cycle of Plasmodium involves both asexual and sexual reproduction. The asexual reproduction takes place in the human host, while the sexual reproduction takes place in the female Anopheles mosquito.

Explanation:
The life cycle of Plasmodium involves the following stages:

1. Sporozoites: The sporozoites are the infective form of Plasmodium, which are injected into the human host by the female Anopheles mosquito while taking a blood meal.

2. Liver stage: The sporozoites enter the liver cells and multiply asexually to form merozoites.

3. Blood stage: The merozoites are released into the bloodstream and infect the red blood cells, where they multiply asexually and cause the symptoms of malaria.

4. Gametocytes: Some of the merozoites differentiate into male and female gametocytes, which are the sexual forms of Plasmodium.

5. Mosquito stage: When a female Anopheles mosquito bites an infected human, it ingests the gametocytes along with the blood.

6. Fertilization: The male gametocytes fertilize the female gametocytes in the mosquito's gut, forming zygotes.

7. Ookinete: The zygotes develop into motile ookinetes, which penetrate the gut wall and form oocysts.

8. Sporozoites: The oocysts release sporozoites into the mosquito's hemocoel, which migrate to the salivary glands.

9. Transmission: When the infected mosquito bites a human, it injects the sporozoites into the bloodstream, and the cycle repeats.

Therefore, the sexual reproduction of Plasmodium takes place in the female Anopheles mosquito, while the asexual reproduction takes place in the human host. Hence, the correct answer is option B.