Kingdom Protista: Introduction, Classification, Characteristics and Examples

 Kingdom Protista:

Protists

    Kingdom Protista is a distinct kingdom of organisms. It includes mostly eukaryotic aquatic organisms. These organisms have characteristics that cannot be classified into any other kingdom. Their mode of nutrition, reproduction, lifestyles, and body forms are different from those of the other four kingdoms. There are four major groups of protists:

• The single-celled protozoa
• Unicellular and multicellular algae
• Slime molds
• Oomycetes

Protozoa: Animal-like Protist

• These are animal-like protists.
• These are unicellular eukaryotic organisms. 
• These are free-living, symbionts, or parasitic. 
• They ingest their food by endocytosis.
• They use cilia, flagella, or pseudopodia for locomotion.

Some common protozoa are:

1. Amoeba
2. Ciliates 
3. Zooflagellates
4. Apicomplexans
5. Actinopods
6. Foraminifera

 Amoeba:

• Amoeba may be free-living or parasitic.
• They are unicellular organisms.
  
• They live in marine, freshwater and soil.
• They have no definite shape.
• Pseudopodia are finger-like special structures, that they use for locomotion.
• They eat dead organic particles through endocytosis.
• Their size ranges from a few micrometers to over 20 cm in diameter. On the other hand, giant amoebas can be up to 10cm in diameter.
• Some examples of ameobas are Entamoeba, Amoeba prosteus, and Acanthamoeba. 

Ameoba

Ciliates:

• Ciliates are unicellular organisms with a definite but changeable body shape.
• They live in an aquatic environment.

• 

  Cilliates

  They are heterotrophs. They consume tiny microorganisms by phagocytosis.
• Some ciliates attach to rock, and some are motile.
• Cillia are short hair-like structures that they use for locomotion. They can move in every direction by these cillia.
  
• They have two nuclei. One is a small diploid nucleus responsible for the sexual process, and the other is a large polyploid nucleus responsible for growth and metabolism.
• Some common examples of ciliates are Paramecium, Trichodina and Colpodina.

Zooflagellates:

• These are unicellular, and some are colonial cellular organisms.
• They are heterotrophs, absorbing organic matter for nutrition.
• Some zooflagellates are free-living, some are symbionts or parasites.
• They move through whip-like structures called flagella. They possess flagella from a single to many.
• They have only one central nucleus.
• They are also aquatic organisms.
• They have a spherical or elongated body.
• Parasitic flagellates cause diseases such as sleeping sickness.
• Some common examples are Trichonympha, Choanoflagelleta, and Trypanosoma.

Apicomplexans:

• Apicomplexans are unicellular parasitic organisms.
• They are obligate parasites (cannot live without their host).
•  They have no specific structure for locomotion.
• Their movement is through flexing. But mostly are non-motile. 
• They consume nutrients from their host. They have a non-photosynthetic plastid. 
• They live part of their life in one host and one part of life in other host(For example plasmodium live in intestine of a mosquito, and when it bite to human, Plasmodium is transferred).
• Some common examples are Plasmodium, Coccidia, and Laeraniina.

Actinopods: 

• They are unicellular organisms.
• They have rod-like pseudopodia, which they use for locomotion.
• They produce shells or tests. This shell acts as a skeleton.
• These shells are made of calcium. Their decomposition produces lime.
• They consume algae or other small microscopic organisms for nutrition.
• Some examples of actinopods are Actinosphaerium, Radiolarians, and Actinophrys sol.

Foraminifera

Foraminifera:

• They are unicellular organisms.
• They are most simple microscopic organisms.
• They are free-living and sometimes symbionts with algae.
  
• They also produce shells of silica or calcium.
• They consume small animals captured through pseudopodia.
• Examples of Foraminifera are Ammonia tepida and Marginopora.

Algae: Plant-like Protist

• Algae are unicellular, colonial, and multicellular eukaryotic protists.
• They are autotrophs. They are primary producer of the aquatic food chain.
• Their body is called a thallus. They lack true stems, leaves, and roots. 
• Their small root hair-like structure is called a rhizoid.
• They have different types of pigments such as chlorophyll a, chlorophyll b, and carotenes.

Some common groups of algae are

1. Euglenoid
2. Diatoms
3. dinoflagellates
4. Green algae
5. Brown algae
6. Red algae

Euglenoid:

• Euglenoids are unicellular organisms.
• Classify euglenoid as either animals or plants has been very difficult for taxonomists.
• Euglenoids are related to zooflagellates, based on molecular data.
• But they have plant-like characteristics.
• They are only photosynthetic in the presence of direct sunlight.
• They become heterotrophs in the darkness. 
• They ingest organic particles for nutrition.
• They have whip-like structures called flagella, used for locomotion.
• Some common examples are Euglena, Astasia, and Phacus.

Diatoms:

• Diatoms are unicellular and colonial algae.
• They are microscopic marine or freshwater organisms.
• There is a large number of diatoms in aquatic ecosystems.
• They are very important in the food chain because they are primary producers.
• They move through water currents.
• Their cell wall produces shells that overlap each other like the two halves of a petri dish.
• These shells are made of silica.
• Some common examples are Cyclotella, Asterionella, and Fragilaria.

Dinoflagellates:

• Dinoflagellates are unicellular but mostly colonial protists.
• The common name of dinoflagellates is dinophytes.
• They have photosynthetic pigments chlorophyll a, chlorophyll b, and carotenes.
• They are also important producer in the aquatic food chain.
• They mostly have two flagella for locomotion.
• When they bloom, it gives red or brown colour to water.
• Their cell wall is in the form of shells.
• Some common examples of dinoflagellates are Ceratium, Gonyaulax and Syndiniales.

Green algae:

• Green algae are unicellular and colonial cellular protists.
• They are very common and well-known protist found in moist and wet places.
• They have photosynthetic pigments chlorophyll a, chlorophyll b, and carotenoids. 
• Green algae are thought to be the first plants on Earth.
• They have flagella for locomotion.
• Some common examples are Carophyte, Chlorella and Ulva.

Red algae:

• These are unicellular or multicellular protists.
• They are called red algae because of phycobilins, a red pigment.
• Some red algae are macroscopic.
• Their rhizoids are attached to rock or soil in the water.
• They take part in building coral reefs.
• They are flattened sheets of cells.
• Some common examples are Coral strands, Polysyphonia, and Irish moss.

Brown algae:

• They are also macroscopic multicellular protists.
• They have a pigment fucoxanthin, which give it a greenish-brown colour.
• They are non-motile.
• They are giants of the kingdom Protista.
• The largest brown algae are kelps. Kelps are tough and leathery.
• Some common examples are Rocky weeds, Wakame and Ectocarpus. 

Fungus-like Protists:

• They are multicellular macroscopic protists.
• They are different from fungi in several characteristics.
• They have a centriole.
• Their cell wall is made of cellulose instead of chitin.
• They have some characteristics related to fungi.
• They contain hyphae.
• They are non-photosynthetic.