A parasite is a micro-organism which is entirely dependent for all or part of its life cycle and metabolic requirements on its host. On the basis of metabolic requirements, there are two types of parasites:
They are always in contact with host and cannot survive without them.
They can live independently of their host, partially on soil.
When parasite requires only one host to complete its life cycle, e.g. Entamoeba histolytica.
Indirect Life Cycle
When two or more hosts are required to complete its life cycle, e.g. Taenia saginata.
It is the host in which the sexual reproduction takes place or most highly developed form exists.
It is the host in which asexual reproduction takes place.
This is an animal host which serves as the source from which other animals are infected.