Kingdom Protista

Kingdom Protista

All single-celled eukaryotes come under this kingdom.

Currently, we include Chrysophytes, Dinoflagellates, Euglenoids, Slime molds, and Protozoans under Protista.

Characteristics of members of Kingdom Protista:-

  • They are primarily aquatic****.

  • Being eukaryotes, the protist cell body contains a well-defined nucleus and other membrane-bound organelles.

    • Some have motile organelles like cilia and flagella.

  • Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.

    • This kingdom forms a link with the others dealing with plants, animals, and fungi.

Dinoflagellates:

  • These organisms are mostly marine and photosynthetic and appear yellow, green, brown, blue, or red depending on the main pigments present in their cells.

  • The cell wall has stiff cellulose plates on the outer surface.

  • Most of them have two flagella - one lies longitudinally and the other transversely in a furrow between the wall plates.

  • Other species of Dinoflagellates are photosynthetic endosymbionts that live in the cell of other organisms such as coral reefs.

    • Very often, red dinoflagellates undergo such rapid multiplication that they make the sea appear red (red tides).

      • Toxins released in such large numbers may even kill other marine animals such as fish.

        • Example: Gonyaulax (red dinoflagellate).

Apicocomplexans

  • They all share the apical complex, a mass of organelle contained in the apical end of the cell.

  • Diseases caused by apicocomplexans:

    • Malaria : by Plasmodium

    • Taxoplasmosis

Ciliates

  • Have hairlike cilia, two types of nuclei, and contractile vacuoles - regulate salt and water balance within the cell.

  • Ex - Paramecium

Stramenopiles

  • Characteristics - descend from ancestors that posses flagella.

  • Oomycetes - not autotrophic

Diatoms

  • Major producers

  • Have silica glass cell wall

  • Go through asexual reproduction followed by sexual reproduction (petri dish or box)

  • They are the chief producers of the ocean.

Brown Algae

  • Multicellular, Orange-yellow pigment due to cholorphyll.

Oomycetes

  • Sperm and zoospores have two flagella.

Sexual stages of Saprolegnia

Rhizaria

  • Unicellular and mostly aquatic

Foraminiferans

  • Bethnic - crawl at the bottom of the ocean

  • Planktonic - Float in the ocean

  • Foraminiferans shells produce limestones.

  • Functions :

    • Locomotion

      • Sticky net for plankton

Radiolarians ➡️

Excavates

  • Mitochondria lost in excavates

Diplomonads

  • The cyst stage of the parasite can be found in river water

Parabasalids

  • Symbiotic with Termites

Heteroloboseans

  • Ex. - Naegleria found in warm fresh water like rivers and lakes.

Euglenoids:

  • The majority of them are freshwater organisms found in stagnant water.

    • They have two flagella****, a short and a long one.

      • Though they are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like autotrophs and heterotrophs by predating on other smaller organisms.

    • The pigments of euglenoids are due to the algae they eat and chloroplast.

      • Example: Euglena.

Amoebozoans

Loboseans

  • Includes plasmodialslime molds and cellular

slime molds and Amoebas

  • Amoebas – Amoeboid Locomotion Using pseudopods

Plasmodial Slime molds

  • Described as coenocytic because the nucleus enclosed in single cell membrane.

  • 4 Stages of plasmodial slime molds exist in :

  • Plasmodial slime molds have fruiting structures when conditions become unfavorable. They feed on multinucleate and cellular feed on single cells.

Cellular Slime Molds

  • Conditions unfavorable - aggregate into a slug. The slug migrates over to construct a dedicated staked fruiting structure.

Protozoans:

  • All protozoans are heterotrophs and live as predators or parasites.

    • They are believed to be primitive relatives of animals.

There are four major groups of protozoans:

Amoeboid Protozoans:

  • These organisms live in freshwater, seawater, or moist soil.

    • They move and capture their prey by putting out pseudopodia(false feet).

      • Marine forms have silica shells on their surface.

  • Some of them are parasites.

    • Examples: Amoeba, Entamoeba.

Flagellated protozoans:

  • The members of this group are either free-living or parasitic.

    • They have flagella.

    • The parasitic forms cause diseases such as sleeping sickness.

      • Examples: Trypanosoma.

Ciliated protozoans:

  • These are aquatic, actively moving organisms because of the presence of thousands of cilia.

    • They have a cavity (gullet) that opens to the outside of the cell surface.

  • The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet.

    • Examples: Paramecium.

Sporozoans:

  • It includes diverse organisms that have an infectious spore-like stage in their life cycle.

    • The most notorious is Plasmodium (malarial parasite) which causes malaria, a disease that has a staggering effect on the human population.

Chrysophytes:

Characteristics:

  • They are found in freshwater as well as in marine environments.

    • They are microscopic and float passively in water currents (plankton)

  • Most of them are photosynthetic.

    • Examples: Diatoms and Golden Algae (Desmids).