Some members of Kingdom Protista
are unicellular, others are colonial, and yet others are multicellular. Note
that in the colonial forms, all the cells are similar with similar, generalized
functions, whereas in the truly multicellular species, the “body” of the
organism consists of a variety of types of cells, each type with its own
specialized function. These organisms are all eukaryotes (they have a true
nucleus). They all need some kind of a water-based environment--which can be
fresh or marine water, snow, damp soil, polar bear hairs--in which to live. All
are aerobic and have mitochondria to do cellular respiration, and some have
chloroplasts and can do photosynthesis. Most of them reproduce or grow by
mitosis, and some reproduce by meiosis and fertilization. Many can form cysts
in adverse conditions. Protists are a major component of plankton.
Protists are grouped into three major, unofficial
categories based on means by which they obtain nutrition. These are the Protozoa,
the Algae, and the Fungus-like Protists. For some reason,
botanists use the word “Division” to mean the same taxonomic level as “Phylum”,
and since, way back everything was lumped in as either a plant or an animal,
taxonomists who study Kingdom Protista (and those who study Kingdom Fungi) also
still use the word “Division” to mean “Phylum”, so for example, when “Division
Rhizopoda” is listed below, that means the same thing as saying “Phylum
Rhizopoda”.