Parasitism: The organisms which depend on other organisms for food, are Parasites. The organisms from which parasites get food is called the host. These parasites obtain food from the host with the help of haustoria. These are called ectoparasite and endoparasite. On the basis of contact with the host. The ectoparasites reside on the surface of host but they penetrate their housteria into the host's cell. Example: Cascuta, Casrytha etc. Santalum, striga, orobenche are examples of total root parasite of roots of plants of solanaceae and cruciferae family. Cuscuta is stem parasite whereas cassytha is total stem parasite on azidiracta (neem tree).
Endoparasite live inside the cells of the host such as viruses, bacteria, mycoplasma etc.