Kingdom Protista

 

Protists are a category of organisms that are very diverse.� They are defined as any organisms that are not a plant, animal, fungus or prokaryote.� They are often referred to as the �garbage� category of classification as their categories of species have only some characteristics of plants, animals, fungus and prokaryotes.� They range from single celled organisms to large masses of organisms.� They are by far, the most diverse kingdom of all organisms.� They are usually broken into three main categories:� animal-like protists, plant-like protists and fungus like-protists.� The majority of protists are benevolent organisms, but some can be parasitic.� It is believed that protist are about 1.5 billion years old.� Some evolutionary scientists would place them as some of the first eukaryotic life on Earth.

 

Animal-like protists can be broken into four sub-categories:� Zooflagellates, Sarcodines, Ciliates and Sporozoans.

Giardia

Drawing of giardia and related species

Zooflagelates are so named because most of them possess one or two flagella.� The flagella help to propel them through their environment using a whip-like tail.� They are most commonly found in lakes and streams.� Some Zooflagelates are parasitic, but most are not.� Some examples are: Giradia lambia and Trichomas vaginalis.��

 

Amoeba

Drawing of an amoeba with cell parts labelled

Sarcodines are also animal-like protists that use pseudopods for movement and feeding.� A pseudopod is an extracellular projection that flows with a fluid membrane for movement called cytoplasmic streaming.� Pseudopods can be used for feeding when they engulf their food and internalize it for digestions.� The best known and most studied Sarcodine is the amoeba.� The amoeba also has an additional organelle known as a contractile vacuole.� The contractile vacuole is used by the amoeba to remove excess water.� This prevents the amoeba from bursting in fresh water environments.

 

Paramecium

Light Microscope Image of a Paramecium

Ciliates are animal-like protists that can be found in fresh water and in salt water.� They are named for the cilia that line the outer portion of their bodies.� The cilia beat quickly to help them move very quickly.� Most Ciliates contain a contractile vacuole to help maintain homeostasis.� A common example of a Ciliate is the Paramecium.� The Paramecium has a very unusual way of creating genetic variety.� It has both a micronucleus and a macronucleus filled with genetic information.� The micronucleus is a �back-up� copy of important genes for the organism.� When two Paramecium go through conjugation, they get very close to each other and exchange micronuclei.� The new micronucleus migrates to the macronucleus where the new genes are integrated into the genome of the organism.

Sporozoans are the last category of animal- like protists.� They are usually parasitic, or disease causing.� The best known Sporozoans cause Malaria and African Sleeping Sickness.� Malaria is caused when the Sporozoan named Plasmodium is carried by a female Anopheles mosquito to a human.� When the mosquito bites the human, tiny sporozoites can enter the blood stream.� They will then incubate in the liver and move on to attack red blood cells.� It is believed that humans who carry the gene for Sickle Cell Anemia are immune to this protist.� Sickle Cell Anemia may have evolved as a human combat tool to evade infection from this parasite protist.

 

Plant-like Protists are broken into the following categories:� Unicellular and Multicellular.

 

The unicellular plant-like protists include: Eugleophytes, Dinoflagellates, Chrysophytes, Diatoms, and Unicellular Algae.�

Euglena

Drawing of euglena with cell parts labelled

Eugleonphytes, also known as Euglea are an interesting type of protist that is both autotrophic and heterotrophic.� Euglena uses an eyespot to sense light.� When light is abundant, it will make its food as an autotroph with photosynthesis.� When light is scarce it has the ability to switch to a heterotroph.

Diatoms are beautiful Dinoflagellates that have calcium carbonate in their bodies.� They make intricate and beautiful arrays of designs.� Some dinoflagellates are harmful.� They have the ability to �bloom� when there are too many nutrients in ocean environments.� They are commonly known as �red tides�.� Some Dinoflagellates are unique because they can bioluminesce.� Bioluminescent diatoms will glow a bluish color in the ocean when agitated.

Chrysophytes are very important to marine life.� The most common Chrysophyte is phytoplankton.� Phytoplankton is often referred to as the base of all marine food chains.� It is the plant-like version of grass in the ocean.� Many first order heterotrophs depend on phytoplankton for survival.�

Chlamydomonas

Drawing of chlamydomonas with cell parts labelled

Unicellular Algae like Chalymdomonas are great examples of a single celled organism.� The possess contractile vacuoles, but also have chloroplasts.

 

 

Fungus-like protists include the following:� Cellular and Acellular Slime Molds.

 

Cellular Slime molds are masses of fungus like protists that have both sexual and asexual life cycles.� Most cellular slime molds will only reproduce sexually when they are under optimal conditions.� They love moist environments where their amoebas can creep to obtain nutrients.� When conditions become unfavorable, they mass into a large aggregate that will migrate to a new location.� They are highly mobile and can move a fair distance.

 

Acellular slime molds only reproduce sexually.� They have the ability to aggregate as well.� They will form a fruiting body when conditions are not favorable.� The fruiting body will release spores with a very hard outer covering.� These spores can resist very long periods of dryness and dessication.� When conditions are good, the spores will create a new slime mold.�