what is protozoa & protoctista ?

Question

what is the relationship between those two terms?
Is protozoa a phylum? class??
I am so confused, please help, really appreciate !!!!!!!!!!1

Answer 1

Protoctista refers to all the organisms that are commonly classified in Kingdom Protista. These organisms are grouped in this kingdom mostly because they don't belong in any other kingdom. It's sort of a miscellaneous "catch-all" kingdom.

The main organisms that are classified in this kingdom are the protozoa, the algae, and the slime molds. Protozoa are divided into several phyla on the basis of their methods of locomotion: with cilia, with flagella, with pseudopodia, or no known method.

Answer 2

Protists (IPA: [ˈprəʊ.tɪst]) are a heterogeneous group of organisms, comprising those eukaryotes that are not animals, plants, or fungi. They are usually treated as the kingdom Protista or Protoctista. The protists are a paraphyletic grade, rather than a natural (monophyletic) group, and do not have much in common besides a relatively simple organization (unicellular, or multicellular without highly specialized tissues). Some call it the "left-overs" from the other eukaryotic kingdoms. Traditional classification:- Protists were traditionally (for the last 150 years) subdivided into several groups based on similarities to the higher kingdoms: the animal-like protozoa, the plant-like algae, and the fungus-like slime moulds and water moulds. These groups often overlap, and have been replaced by phylogenetic classifications. However, they are still useful as informal groups for describing the morphology and ecology of protists. At one time, bacteria were also considered protists, under the three-kingdom system of Animalia (corresponding closely to the modern kingdom), Plantae (which included Fungi as well as plants), and Protista (everything else). See kingdom (biology). However, most recent texts treat bacteria separately. Phylogenetic classifications:- The classification of protists is still changing. Newer classifications attempt to present monophyletic groups based on ultrastructure, biochemistry, and genetics. Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes. The recent scheme by Adl et al. (2005) is an example which does not bother with ranks (phylum, class, etc.). Some of the main groups of protists that are now recognized, which may be treated as phyla, are listed in the taxobox at right. Some smaller groups are listed under the traditional categories, linked to above. For more discussion of relationships between different protists, see eukaryote or the articles referenced below.

Answer 3

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.

No one knows how many species of protoctists there really are; thousands have been described in the biological literature. Water molds and plant parasites have traditionally been dealt with by the mycological literature, parasitic protozoa by the medical literature, algae by the botanical literature, free-living protozoa by the zoological literature, and so forth. Inconsistent practices of describing, naming, and defining species has led to a great deal of confusion regarding these organisms. Another reason for ignorance is that the group of eukaryotic microbes is large, with much diversity in tropical regions, whereas protozoologists are scarce and concentrated in the north temperate zones. Furthermore, distinguishing species of free-living protoctists often requires time-consuming genetic and ultrastructural studies. Funding for such studies is limited because most protoctists are not sources of food and cause no diseases; thus, they are of no direct economic importance.

The protoctists show remarkable variation in cell organization, patterns of cell division, and life cycle. Some are photoautotrophs, which make oxygen; others are ingesting or absorbing heterotrophs (such as phagotrophs or osmotrophs). In many species, the type of nutrition depends on conditions: when light is plentiful, they photosynthesize; in the dark, they feed. However, although protoctists are far more diverse in life style and nutrition than are animals, fungi, or plants, they are far less diverse metabolically than the bacteria.