what is the defination if protocista?

Question

pleeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeease help me. i have got a exam tomorrow

Answer 1

Kingdom Protoctista is defined by exclusion: its members are neither animals (which develop from a blastula), plants (which develop from an embryo), fungi (which lack undulipodia and develop from spores), nor prokaryotes. They comprise the eukaryotic microorganisms and their immediate descendants: all nucleated algae (including the sea-weeds), undulipodiated (flagellated) water molds, the slime molds and slime nets, and the protozoa. Protoctist cells have nuclei and other characteristically eukaryotic properties; most have aerobiosis and respiration in mitochondria and 9+2 undulipodia at some stage of the life cycle.

Why "protoctist" rather than "protist?" Since the nineteenth century, the word protist, whether used informally or formally, has come to connote a single celled organism. In the last two decades, however, the basis for classifying single-celled organisms separately from multicellular ones has weakened. It has become evident that multicellularity evolved many times from unicellular forms - many multicellular organisms are far more closely related to certain unicells than they are to any other multicellular organisms. For example, the ciliates, which are unicellular microbes, include at least one species that forms a sorocarp, a multicellular spore-bearing structure; euglenoids, chrysophytes, and diatoms also have multicellular derivatives.

Protoctists are aquatic: some primarily marine, some primarily freshwater, and some in watery tissues of other organisms. Nearly every animal, fungus and plant - perhaps every species - has protoctist associates. Some protoctist phyla include hundreds of species, all of which are parasitic on other organisms.

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Answer 2

as i understand it, this kingdom is now regarded as defunct. If you are still being taught this, then it is worrying.