Final answer:
The definitive host is where a parasite reaches maturity and reproduces, such as the Anopheles mosquito for Plasmodium falciparum. Hence, the statement is True.
Step-by-step explanation:
The organism in which a parasite reaches maturity and reproduces is indeed the definitive host. This is because definitive hosts are those in which the parasite becomes adult and is capable of sexual reproduction (if the parasite reproduces sexually). For example, Plasmodium falciparum, the causative agent of malaria, reproduces asexually in the human host, but it reaches its reproductive (sexual) stage in the gut of the Anopheles mosquito, making the mosquito the definitive host. Similarly, for tapeworms, humans often serve as the definitive host because it is within the human gut that the tapeworm matures and produces eggs. Therefore, the correct answer to the question is A) True.