Final answer:
Symbiosis is a close relationship between two organisms of different species. Bacteria can form three types of symbiotic relationships with a host: mutualism, commensalism, and parasitism.
Step-by-step explanation:
Symbiosis is a close relationship between two organisms of different species in which at least one of the organisms benefits. There are three basic types of symbiosis: mutualism, commensalism, and parasitism.
In mutualism, both the host and the bacteria benefit from the relationship. An example of this is the relationship between bacteria in our gut and us. They help us digest food and we provide them with nutrients.
In commensalism, the bacteria benefit from the relationship, while the host is not affected positively or negatively. An example of this is the bacteria that live on our skin. They are not harmful to us, but they do not provide any benefit either.
In parasitism, the bacteria benefit from the relationship, while the host is harmed. An example of this is the bacteria that cause infections or diseases in humans.