Protoctists

Protoctists are eukaryotes that include single-celled organisms such as amoeba or chlorella and cells grouped into colonies. Colonial protists include Volvox: a single Volvox colony contains anywhere from 500 - 60,000 cells.Some protists, such as green algae (Chlorophyta), are multicellular.They have a variety of feeding mechanisms and use plants or animals as their host.Some protists, such as Euglena have chloroplasts and are photosynthetic.A small percentage of protoctists are pathogenic such as Plasmodium spp. that causes malaria.The protists may need a vector to transfer them to their hosts.Malaria and sleeping sickness use insect vectors. Amoebic dysentery and Giardia enter the body through polluted water.