Protists are the simplest eukaryotic organisms.  Like monerans, protists come in diverse forms.  They are sometimes described as animal-like or plant-like.  But unlike plants and animals, protists lack tissue differentiation.  Plantlike protists are collectively called protozoans, while animal-like protists called algae.

The protist kingdom includes unicellular organisms and some simple multicellular organisms. But unlike monerans, a protist cell has a nucleus and other organelles in the cytoplasm. Protist live in a watery environment. Some protists have chlorophyll. These protists make their own food by photosynthesis. Other protists live on living or dead organisms to obtain food and energy.

The Kingdom Protista includes the protozoans, algae, fungus-like and other groups of relatively unfamiliar organisms. Some protists have the characteristics similar to plants. Other protists have the characteristics similar to animals.

1.  Plantlike Protists:  ALGAE

All plantlike protists have chlorophyll like those in plants. This green substance in their cells enables them to make food by photosynthesis. In the same process, they produce and release oxygen as plants do. In fact, most of the supply of oxygen on Earth is believed to come from plantlike protists. The plantlike protists are also the major food source for water organisms.

Phylum Chlorophyta:  Green Algae

The green algae include both unicellular and multicellular algae.  The  spirogyra is freshwater unicellular green alga.  It grows as a green thread or filament.  Each thread is actually made of many individual cells joined end to end in a chain.

The ulva or sea lettuce is a multicellular green alga. It grows in seas and oceans.

 Chlamydomonas is an example of one-celled green alga.

Spyrogyra, a freshwater alga with spiral shaped chloroplasts, and the ball-like colonial Volvox.

Phylum Rhodophyta:  Red Algae

The red algae are mostly large and multicellular.  They grow in the oceans.  Their red pigment usually masks the green color of the chlorophyll.  One kind of red algae is used as food in Japan.  Also, red algae have glue-like substances in their cell walls; carrageenan and agar.  Agar is the food substance used from growing bacteria and other organisms for laboratory studies.  Agar is used to make gelatin capsules, the material for making dental impressions and a base for cosmetics.  It is also a main ingredient in the laboratory media in which bacteria, fungi, and other microorganisms are grown.  Carrageenan is used mainly as a stabilizer and thickener in dairy products such as creamed soups, ice cream, and whipped cream, and a stabilizer in paints and cosmetics.  It is also used to give toothpaste and pudding their smooth creamy textures.

Phylum Phaeophyta:  Brown Algae

The brown algae are multicellular.  They usually grow on rocks in the shallow seawaters.  Large brown algae called kelps may grow as long as 100 meters.  They are among the longest organisms in the world, rivaling the height of the giant Sequoia trees.  These algae usually have a rootlike structure called holdfast, which anchors the seaweed to the ocean floor or rocks.  A steamlike stipe carries the leaflike blades, which afloat in the water, capturing the sun’s ray.  Kelps may grow densely in the sea, forming a kelp forest.  Many kelps are important food sources for fish and invertebrates.  They form dense mat of stalks and leaflike blades where many small fish and other animals live.  The type of brown algae that grow attached to rocks at the shoreline are called rockweed.  Their puffy air bladders keep the plant afloat during high tide.  An example of rockweed is Sargassum.  Some brown algae are source of algin, a substance used as an ingredient in making ice cream, lotion, and plastics.

Phylum Chrysophyta:  Golden Algae

The prefix chryso means color of gold.  This color is due to the bleeding of three pigments: the orange carotenes, the yellow xanthophylls, and the brown fucoxanthins.  An unusual characteristic of these golden algae is that they store food in the form of oil.

There are three types of golden algae:  Yellow-green Algae, Golden-brown Algae, Diatoms.  The most numerous of all algae are the diatoms.  They are abundant in both seawater and freshwater environments.  The shells of diatoms contain silica, the main element in glass making.  They look glassy under the microscope.  The body of a diatom is like a small box with a lid.  One half of the shell fits in the other half.  Diatoms live in freshwater and salt water habitats.  They are important food source of many aquatic organisms.  The shells of fossil diatoms form thick deposits on the sea floor, also known as diatomaceous earth.  This is sometimes mined commercially.  It is used as water filters, as an abrasive, and to add the sparkling quality of products, such as the paint used on roads and frosted fingernail polish.

Phylum Pyrrophyta:  “Fire” Algae

Phylum Pyrrophyta contains species of one-celled algae called dinoflagellate.  The term dinoflagellate literary means ‘spinning swimmers’.  Dinoflagellates have two flagella.  One flagellum moves the cell while the other circles the cell, causing it to spin like a top.  They store food in the form of starch and oils.  Their red color is due to chlorophyll a and c, and xanthophylls.  Fire algae glow at night like a neon light when disturbed.  This ability of organisms to emit light is called bioluminescence.

Almost all species of dinoflagellates live in seawater.  Some species of dinoflagellates cause the red tide phenomenon.  Every once in a while, especially in summer for some known reasons like pollution, certain species of dinoflagellates experience population explosion or algal bloom in coastal areas which causes the water to take on a reddish hue.  Some dinoflagellates that cause red tide such as the Gonyaulax, contain a neurotoxin that kill fish, birds, and marine mammals.  Shellfish, which are filter feeders, strain these dinoflagellates from the water and store them in their bodies.  People who eat fish or shellfish that have absorbed the toxins produced by these algae can become ill and sometimes die.

2.  Animal-like Protists:  Protozoans

Animal-like protists have characteristics similar to multicellular animals. They do not have chlorophyll. They cannot make their own food. They depend on other organisms for food and energy. Animal-like protists are called protozoans.

All protozoans live in moist or watery environments. They live in oceans, fresh waters, and in moist soil. Some kinds of protozoans can live in animal tissues. Protozoans are grouped according to how they move about. Ciliates, flagellates, amoebas, slime molds, and sporozoans are all different protozoans.

Phylum Ciliophora: Ciliates

Protozoans called ciliates move by means of hairlike structures called cilia that stick out of their cells. Cilia sway back and forth like paddles in the water. The fast beating of the cilia moves the organism. The cilia are also used to sweep floating food particles into the organism. The paramecium is an example of a ciliate protozoan. Paramecia are frequently found in freshwater ponds. Paramecium is shaped like a slipper and has distinct front and back ends. It has two nuclei called micronucleus and macronucleus that direct the cell’s activities. Food is swept into the oral groove then into the mouth pore. Enzymes digest food inside the food vacuoles. Undigested wastes leave the cell through the anal pore. Paramecium reproduces asexually by means of binary fission or through conjugation.

Phylum Mastigophora: Flagellates

Flagellate protozoans move by means of flagella. Most flagellates are parasitic. Many flagellates live in the intestines of humans, in termites, and other animals. Some flagellates are harmful. Trypanosoma gambiense, is a flagellate that causes the African sleeping sickness in cattle and humans. These protozoans are carried by tsetse flies. A person becomes infected when bitten by a tsetse fly. Once inside the body, the trypanosomes reproduce and invade the fluid surrounding the brain and the spinal cord. The infected person experiences high fever and sleepiness.

Euglena is another flagellate that also has features of plant like protists. It has chloroplasts like algae and flagella like protozoans. It is for this reason that it is sometimes placed in a separate phylum. Euglena reproduces asexually by means of longitudinal binary fission, a simple mitotic division where a cell splits lengthwise into two.

Phylum Sarcodina

Sarcodines move by means of the tiny fingerlike projections of their cytoplasm and cell membrane called pseudopodia. Other protozoans move by forming pseudopods. Pseudopod means false foot. Sarcodines feed on dissolved nutrients, other microscopice organisms and tiny bits of food. They live in muddy freshwaters, and at the ocean bootom, and in contaminated drinking water. The most common example of sarcodines is Amoeba. One species, Amoeba histolytica, causes amoebic dysentery or amoebiasis in humans. Amoeba reproduce by binary fission. When conditions are unfavorable, the cell membrane of amoeba thickens and forms a cyst. Inside the cyst, the nucleus divides in a process called multiple fission. The new amoebas are released when conditions becaome favorable. This is one reason why treatment of amoebiasis is difficult and take time.

Phylum Sporozoa

All members of Phylum Sporozoa are nonmotile and parasitic. Since they have locomotory structure, they are carried by the body fluids of their hosts. Many sporozoans cause serious disease in humans. An example is Plasmodium, a parasite that causes malaria.

Malaria is a disease caused by the spore-forming sporozoan called plasmodium. This protists is carried in the body of the female Anopheles mosquito. The bite of this mosquito injects the plasmodium into the person’s bloodstream, destroying the red blood cells as they reproduce. The infected person experiences high fever and chills. Often times, malaria causes death. Another malaria-like parasite belongs to the genus Babesia. This one-celled organism invades red blood cells and many cause fatigue, aches, fever, chills, sweating, dark-colored wine enlarged spleen, or anemia. The disease is called Babesiosis and can be transmitted to humans by ticks.

3.  Fungus-like Protists

Fungus-like protists are heterotrophic, they cannot make their own food, and thus they must be able to move at some point in their lives. These protists contain long hyphae-like strands thus they contain the physical appearance of fungi. The difference lies in that the hyphae of fungi are white while the hyphae of protists are usually bright in color.

The fungus-like protists can act as decomposers. They break down dead organisms by releasing digestive enzymes into the dead organism. In the end materials useful to other living organisms are released into the surrounding environment. Two examples of the fungus-like protists are:

Water Molds

Water molds are fungus-like protists that live in moist environments. They look like tiny threads with a hazy covering (when in a damp environment). Most water molds are decomposers, breaking down dead organisms; few water molds are parasites, living in or on other organisms.

Water molds attack foods such as potatoes, cabbage, and corn. They are capable of completely destroying crops. An example of the devastation a water mold is capable of doing happened between the years of 1845 and 1860. The growing seasons at this time was a cold and damp one; these are conditions that encourage the spread of the water mold Phytophthora infestans. This water mold is the cause of rotting potato plants (late blight). It infested all of the potato crops in Ireland. During this period one third of Irelands population died; they either starved to death or were killed by the infested potatoes.

Slime Molds

Slime molds are a fungus-like protist that lives in moist soil, decaying plants, and trees. They have a very bright appearance.

Slime molds are single celled organisms. When conditions become unfavorable the single celled organisms join together and act like a "multi-cellular" organism. The protists will then form a sporangia-a cluster of cells on top of a stalk. The sporangia consist of living cells in a dormant stage, while the stalk consists of dead cells that act as a foot and push the cells to favorable conditions. When conditions become favorable the "multi-cellular" organism separates itself back into the single celled organisms.

 

Related posts:

1. Taxonomy: Kingdom Monera
2. Taxonomy: Kingdom Plantae
3. Taxonomy: Kingdom Mycetae (Fungi)
4. Taxonomy: Brief History of Taxonomy
5. Taxonomy: Kingdom Animalia