Explanation

A disease vector is an organism that carries and transmits disease from one host to another. Mosquitoes carry malaria parasites in their bodies. When a mosquito bites someone, it transfers the parasites into that person blood, spreading the disease.

The mosquito itself is not a microorganism but acts as a vector for the microscopic malaria parasite. The mosquito picks up parasites when biting infected people and passes them to healthy people through later bites. This makes mosquitoes dangerous disease spreaders.

Bacteria causing food poisoning infect directly, not through a vector. Fungi decomposing plants and algae making oxygen are not disease-related. Only mosquitoes serve as vectors by carrying disease-causing microorganisms between hosts.