Protists are mostly single-celled organisms and are one of the simplest forms of life. They are the first Kingdom containing eukaryotic organisms, and are one of the most diverse kingdoms. In the modern classification of organisms, the protista can be divided into three categories:

• Plant-like protists:

• Fungi-like protists:

• Animal-like protists:Volvox

Water mold

Paramecium

(Protozoans)

Plant-like protists are autotrophic. They can live in soil, on the bark of trees, in fresh water, and in salt water. These protists are very important to the Earth because they produce a lot of oxygen, and most living things need oxygen to survive. Furthermore, these plant-like protists form the base of aquatic food chains.Plant-like protists can be unicellular, multicellular, or colonial. The plant-like protists are divided into four basic groups: euglenoids, dinoflagellates, diatoms, and algae. Cells found within colonial

Protists are capable of living independently. Cells in multicellular organisms are incapable of this. They become specialized and carry out specific functions. If you remove a cell from a multicellular organism, even though it has the genetic capability to live, it could not.

are free-living, flagellated cells with autotrophic, and heterotrophic feeding modes. Euglena, a typical euglenoid, is covered by a flexible protein pellicle, possesses an eyespot, flagellum, and is photosynthetic.

• photosensitive

• mixotrophs

Dinoflagellates are mostly marine phytoplankton.

These plant-like Protists are sometimes referred to as the “Cells from Hell”, perhaps because of the damage they can do.

Their ability to undergo stupendous increases in population size in a relatively short time frame are responsible for a coastal event known as “red tide”.These phytoplankton produce toxins that kill many organisms in the affected area, also known as a fish-kill.The addition of nutrients like nitrogen, and phosphorus to the agricultural soils of the mid-west, can initiate these red tides.Some forms of the red-pigmented cells also produce a neurotoxin fatal to humans and other animals.

possess chlorophylls a and c, but other pigments (fucoxanthin) mask the green color to give shades of yellow color to the algae. The siliceous (glass-like) shells of the diatoms form intricate geometric patterns that are circular or spindle shaped. The patterns are useful in the classification of the group. The diatoms are an important phytoplankton group.

used to designate a large group of (mostly) photosynthetic protistans, the majority of which are phytoplankton, the single-celled photosynthetic cells suspended in bodies of water. There are several groups.

The advanced plant-like protista included the large colonial seaweeds: red and brown algae. These forms have advanced body structure and border on being truly multicellular. Some botanists even classify these Protistans in the Plant Kingdom as primitive groups. Red Algae (Rhodophyta) possess phycobilin pigments, which can trap sunlight in deep marine waters.

Brown Algae (Phaeophyta) includes the large kelps of the intertidal zones. Xanthophylls, chlorophylls, and other pigments provide the color. They are very plantlike in structure: Leaflike blades grow from a stemlike stipe, which may be attached to a rootlike holdfast. Some, like our east coast Fucus have gas-filled bladders, or floats.

(Chlorophyta) grow virtually everywhere and bear the greatest resemblance to land plants of any of the algae suggesting a possible evolutionary link. They have the same pigments as land plants (chlorophylls a and b, carotenoids, anthocyanins and xanthophylls).

They possess cellulose in the cell walls and store carbohydrates as starch. The modes of reproduction are quite diverse. Examples include the simple Chlamydomonas, and the Spirogyra, which forms conjugation tubes between adjacent filaments through which cell contents move during “genetic exchange."

Fungus-like protists are heterotrophs with cell walls. They also reproduce by forming spores. All fungus-like protists are able to move at some point in their lives. There are essentially three types of fungus-like protists: water molds, downy mildews, and slime molds.

Protists that are classified as animal-like are called protozoans and share some common traits with animals. All animal-like protists are heterotrophs. Likewise, most animal-like protists are able to move in their environment in order to find their food. Unlike, animals, however, animal-like protists are all unicellular. Protozoans are divided into four basic groups based on how they move and live.

Creeping and oozing

Fluttering

Wiggling and whipping

Moseying, and hitching a ride

Sarcodina/PseudopodaSarcodina/Pseudopoda

Ciliophora

Flagellates/Zoomastigina/Mastigophora

Sporozoans

Sarcodina—protozoans that use pseudopods for locomotion. These are the creeping/oozing protists.

Examples: Amoeba, Radiolaria, Naegleria

Ciliophora—protozoans that have and use cilia for locomotion or to create currents to filter food from their environment. These are the fluttering protists.

Examples: Paramecium, Stentor, and Vorticella

Stentor are one of the largest protozoa found in water, and is therefore one of the easiest to study.

Zoomastigina—protozoans that have one or more flagella that are used for locomotion. These are sometimes also called mastigophora. Many are disease-causing. These are the wigglers, and whippers.

Examples: Trypanosoma, Leishmania, Giardia, Trichonympha

Parasitic Protozoans—protozoans that feed on other living organisms and usually cause sickness.Example: Trypanosoma (sleeping sickness-flagellate), and Plasmodium (malaria), Coccidia, and Piroplasms

  

Sporozoans-These protists are characterized mainly by the way they live.  They do not have a mode of transportation of their own, but rely on the host to move them along. All of these protists are parasites.  Many of these protists cause diseases such as malaria. These mosey along.

• All Protozoa can Reproduce ASEXUALLY, usually by binary fission. 

During binary fission, a protozoan divides into TWO identical individuals.

Some species reproduce by MULTIPLE FISSION, a form of cell division that results in a number of identical individuals. A few species also reproduce SEXUALLY, through CONJUGATION.

During conjugation, individuals from opposite mating strains pair and exchange genetic material (DNA).  Conjugation in protozoa is more complex than in Bacteria.