Commensalism is a relationship in which one organism benefits while another one is unaffected. An example of commensalism is the relationship that can exist between cattle and birds. Cattle stir up insects by moving and birds eat the insects.

Parasitism is a relationship in which one organism benefits at the expense of another. As an example, tapeworms can be ingested by animals through food. The tapeworms then consume nutrients intended for the animal, sometimes killing it.

The following video provides examples of symbiotic relationships that exist between different species.