Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy. Instead, it is "better regarded as a loose grouping of 30 or 40 disparate phyla with diverse combinations of trophic modes, mechanisms of motility, cell coverings and life cycles."
The protists do not have much in common besides a relatively simple organization either they are unicellular, or they are multicellular without specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.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.
Examples
- Paramecium
- Amoeba
- Giardia
- Trichonympha
No comments:
Post a Comment