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 protistan 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.

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====).==

Diatoms:

• The cell walls form two thin overlapping shells, which fit together as in a soap box.
  • The ^^walls^^ are embedded with silica and thus the walls are %%indestructible%%%%.%%
  • They leave behind large amounts of cell wall deposits in their habitat and this accumulation over billions of years is referred to as diatomaceous earth.
    • This soil is used in ^^polishing, and filtration of oils and syrups^^ since it is gritty.
• They are the %%chief producers of the ocean.%%

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.
  • 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 @@fishes.@@
    • Example: ^^Gonyaulax^^ (red dinoflagellate).

Euglenoids:

• The majority of them are freshwater organisms found in stagnant water.
  • Instead of a cell wall, they have a @@protein-rich layer called a pellicle@@ which makes their body flexible.
  • 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 heterotrophs by predating on other smaller organisms.
  • The pigments of euglenoids are identical to those present in higher plants.
  • Example: ^^Euglena.^^

Slime Moulds:

• They are %%saprophytic%% protists.
• The body moves along decaying twigs and leaves %%engulfing organic material.%%
  • Under suitable conditions, they ^^form an aggregation^^ ^^called^^ ^^plasmodium^^ which may grow and spread over several feet.
  • During unfavorable conditions, the ^^plasmodium differentiates and forms fruiting bodies bearing spores^^ at their tips.
  • These spores possess %%true walls and are dispersed by air currents.%%
  • They are extremely ^^resistant^^ ^^and^^ ^^survive for many years^^^^,^^ even under adverse conditions.

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.^^

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