What is a single celled organism able to do?

The one cell of a unicellular organism must be able to perform all the functions necessary for life. These functions include metabolism, homeostasis and reproduction. Specifically, these single cells must transport materials, obtain and use energy, dispose of wastes, and continuously respond to their environment.

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.