Kingdom Protista

• simplest eukaryotes but an incredibly diverse group

• defined by exclusion :

- not bacteria (they are prokaryotic)

- not plants or animals (they develop embryos)

- not fungi (they develop from spores)

• they represent an important step in early evolution, evolving from prokaryotes and eventually giving rise to the entire line of eukaryotes

[The common point for all eukaryotic branches]

• the first protists probably evolved between 1.5 and 1.7 billion years ago, 2.3 billion years after the origin of life, from simple communities of prokaryotic cells

• most unicellular

• some colonial

• some simple multicellular (protoctista)

[anybody know any multicellular protists?]

• some are autotrophic photosynthesizers (algae), rest eat bacterial or other protistan cells, or small suspended or dissolved organic particles

• thrive in aquatic habitats

• movement provided by one or more flagella and/or cilia

• nuclei contain multiple DNA strands

• can reproduce mitotically, some can do meiosis

• cellular respiration is primarily aerobic, some are strict or facultative anaerobes

• nearly every animal, plant, and fungus – perhaps every species – has protist associate

• no one knows how many species of protists there really are; thousands have been described

• distinguishing species of free-living protists often requires

time-consuming genetic and ultra-structural studies and funding is limited because they are of no direct economic importance

• remarkable variation in cell organization, patterns of cell division, and life cycle

• far more diverse in life style and nutrition than are animals, fungi, or plants, they are far less diverse metabolically than the bacteria

• suggested that the major protist phyla are so distinct as to

deserve kingdom status

• Kingdom Protista videos :