OVERVIEW OF PROTOZOA

The Kingdom Protista contain a diverse collection of Eukaryotic organisms, protozoa, algae, slime molds, and water molds.  Collectively, these organisms are called Protists.  Protists are sometimes described as animal-like, plant-like, and fungi-like.  However, all protists are Eukaryotic and lack tissue differentiation.

OBJECTIVES:  Describe the characteristics of protozoa. Explain the role some protozoa play in aquatic ecosystems.  Discuss the classification scheme used to identify protozoa.  Name an adaptation that enables some protozoa to survive harsh environmental conditions.  Briefly explain the evolution of protozoa.

CHARACTERISTICS

1. Protozoa are Single-Celled microscopic Eukaryotic organisms that are noted for their ability to Move Independently.

2. Protozoa are sometimes referred to as Animal-Like Protists.

3. Biologist have identified about 65,000 species of protozoa, almost half which are extinct species from fossils.

4. Protozoa live in many different environments; they can drift in the ocean, creep across vegetation in fresh water rivers and ponds, crawl in deep soil, and even reproduce in the bodies of other organisms.

5. Most Protozoa are HETEROTROPHIC, obtaining their nutrients by ingesting small molecules or cells.  These particles are usually broken down in FOOD VACUOLES, membrane-bound chambers that contain Digestive Enzymes.

6. Many species are free-living, while others are Parasites.

7. Free-living live in any habitat where WATER or MOISTURE is available at some time during the year.

8. Many species make up ZOOPLANKTON, a population of organisms that constitutes one of the primary sources of energy in Aquatic Ecosystems.  They are the beginning of the Food Chain.

9. Some Free-Living Protozoa live in the soil.

10. Parasitic Protozoa usually have Complex Life Cycles that take place in the cells, tissues and bloodstream of their Host.  Several species cause serious human diseases, including Malaria, Amebic Dysentery and Giardiasis.

REPRODUCTION

1. All Protozoa can Reproduce ASEXUALLY, Usually by Binary Fission.  During binary fission, a protozoan divides into TWO Identical Individuals.

2. Some species reproduce by MULTIPLE FISSION, a form of Cell Division that results in a Number of Identical Individuals.

3. While ALL species can reproduce Asexually, a few also reproduce SEXUALLY, through CONJUGATION.

4. During Conjugation, individuals from Opposite Mating Strains Pair and Exchange Genetic Material (DNA).  Conjugation in protozoa is more complex than in Bacteria.

CLASSIFICATION

1. Protozoa are members of the Kingdom Protista, along with Algae (plant-like), and Slime Molds, and Water Molds (Fungi-like).

2. A Convenient way to classify Protozoans is based on the WAY THEY MOVE:  THE FOUR PHYLA OF PROTOZOANS ARE: 

   A. PHYLUM SARCODINA (SCARCODINIANS) MOVE BY EXTENDING THEIR CYTOPLASM.  

   B. PHYLUM ZOOMASTIGINA (ZOOFLAGELLATES) PROPEL THEMSELVES
BY FLAGELLA. 
  

  C. PHYLUM CILIOPHORA (CILIAPHORANS) OR CILIATES MOVE BY HAIRLIKE CILIA. 

    D. PHYLUM SPOROZOA (SPOROZOANS) DO NOT MOVE BY THEMSELVES AT ALL.
 

ADAPTATIONS

1. Many species have physiological mechanisms for Monitoring Conditions in their Environment.

2. Many free-living species have a localized Region of Pigment called an EYESPOT.  Eyespots detect Changes in the Quantity and Quality of Light.

3. Certain Protozoan species also sense physical and chemical changes or Obstacles in their environment.

4. Most Protozoa are separated from their Environment Only By their Cell Membrane.

5. They can survive in Extreme (Harsh) Conditions due to their ability to form CYSTS.  A Cysts is a Dormant Form characterized by a Harden External Covering in which Metabolic Activity has Ceased.

6. Many species form Cysts in response to Changes in the Environment, such as Nutrient Deficiency, Drought, Decreased Oxygen Concentration, or pH or Temperature Changes.

7. Cyst formation is important to many Protozoa that must survive such conditions between Host.

8. When Favorable Environmental condition Return, a Protozoan emerges from the Cysts and resumes Metabolic Activity.

EVOLUTION

1. The First prokaryotes evolved more than 3.5 years ago, about 1.5 billion years ago the First Eukaryotic Organisms Evolved.  Protozoa are the descendants of these early Eukaryotes.

2. The first Eukaryotes Probably evolved through ENDOSYMBOSIS, a process in which one prokaryote lives inside another and Gradually both host and guest become dependent on one another. (Read:  The Origin of Eukaryotic Cells)

PROTOZOAN DIVERSITY

The broad diversity of protozoa is evident in the four major phyla identified by biologist.  The phyla are distinguished by their Form of Locomotion, and each group contains a number of Parasites that causes serious human disease.  The complexity of protozoa sets them apart from the relatively simple structures of bacteria and viruses.

OBJECTIVES:  Explain how sarcodines have contribute to Earth's geological features.  Explain how the four groups of protozoan move.  Describe a type of sexual reproduction that occurs in ciliates.  Identify four human diseases caused by zooflagellates.  Discuss the life cycle of Plasmodium.

PHYLUM SARCODINA (SAHR-kuh-DE-nuh), SARCODINIANS

1. Biologists have classified 40,000 species of protozoa in the Phylum Sarcodina.

2. Sarcodines include hundreds of Species of Amoebas, which inhabit fresh water, salt water, and soil.  Some can even live on mud, rocks, and other surfaces in shallow, slow moving streams and ponds.

3. SARCODINIANS ARE PROTOZOANS THAT MOVE BY EXTENDING LOBES OF CYTOPLASM.

4. The lobes of Cytoplasm that Sarcodinians extend are called PSEUDOPODS (PSEUDOPODIA), WHICH MEANS "FALSE FOOT".

5. A Pseudopodia forms when ENDOPLASM, the inner portion of Cytoplasm, pushes the ECTOPLASM, the Outer Layer, forward to Create a Blunt, armlike Extension.

6. Amoebas move by extending part of their cell membrane into a lobe, or pseudopodia, that can attach to a surface.  Then, Cytoplasm streams into the pseudopodia and pulls the organism forward.  This movement is called AMEBOID MOVEMENT.  Ameboid Movement is a form of CYTOPLASMIC STREAMING, the Internal flowing of a Cell's Cytoplasm. 

7. Sarcodines also use Pseudopodia for Feeding.  Sarcodines live on other protists, which they engulf (eat) by Phagocytosis.

8. When a Sarcodine feeds, it surrounds the food with its Pseudopodia.  A portion of the Cell Membrane then pinches together and surrounds the food in a Food Vacuole, in a process called Endocytosis.  Enzymes from the cytoplasm then enter the Vacuole and digest the food.  Undigested food leaves the cell in a reverse process called Exocytosis.

9. Most fresh water Sarcodines have CONTRACTILE VACUOLES, an organelle that removes excess water from the cell.

10. When conditions are unfavorable, amebas survive by becoming hard CYSTS.  THE CYSTS CAN WITHSTAND DROUGHT, HEAT, OR BEING EATEN BY OTHER ORGANISMS.

11. Not all Sarcodinians are soft "Naked"; many have Hard Shells or TEST, of Calcium Carbonate or Silica and are called:

FORAMINIFERANS AND RADIOLARIANS.  

12. Most hard shell Sarcodinians live in the Ocean, and are important food sources for many marine animals.

13. When hard shelled Sarcodinians die, their shells sink to the bottom of the ocean making huge deposits of limestone called Chalk.  The most famous chalk deposits are the Cliffs of Dover on the coast of England. The Great Pyramids of Egypt were built with stones quarried from Limestone Beds that are made from a Large Foraminiferan.

HUMAN DISEASE

1. Amoebas (Entameba histolytica) as CYSTS can spread by Water, in Food, or on Dishes causing AMEBIC DYSENTERY which can be Fatal.

2. It lives in the Large Intestines, where it secretes Enzymes that attack the Intestinal Lining and causing deep Ulcers. Affected individuals feel intense pain, and complications arise when the amoebas are carried by the blood to the liver and other organs.

3. This is where the saying "Don't Drink the Water" in certain countries comes from.  Travelers are warned never to drink UNTREATED WATER to avoid Amebic Dysentery.

PHYLUM CILIOPHORA, CILIAPHORANS or CILIATES

1. The 8,000 species that make up the Phylum Ciliophora swim by means of CILIA, which are short, hairlike cytoplasmic projections that line the cell membrane.

2. THE CILIATES ARE PROTOZOANS THAT HAVE BODIES COVERED WITH SHORT HAIRLIKE PROJECTIONS CALLED CILIA.

3. The Cilia is used for movement by Beating like Oars to propel the Protists.

4. Some kinds of Ciliates have specialized Cilia shaped like Teeth, Paddles, or Feet.

5.  Most Ciliates live in Freshwater.  A common freshwater ciliate is the Paramecium.

INTERNAL STRUCTURES

1.  Ciliates have the most ELABORATE ORGANELLES of any protozoa. 

2. Paramecia have a protective covering over their Cell Membrane, it is a Clear, Elastic Layer of Protein, called a PELLICLE.

3.  Protozoan both eats and swims through water with it's Cilia.

4.  When Eating, the Cilia sweeps food particles, such as microscopic Algae and Bacteria, into the ORAL GROOVE.  In the Oral Groove, the MOUTH PORE opens into a GULLET, which pinches off around them to form a FOOD VACUOLES. 

5. The Food Vacuoles move inside the Cytoplasm where nutrients are extracted, it ejects the waste through an opening called the ANAL PORE.

6.  ALL PROTOZOANS HAVE CONTRACTILE VACUOLES.  These are an important adaptation for living in Water.  Contractile Vacuoles collect excess water (Osmosis) and pump it outside the Cell body.

7.  Paramecium, LIKE ALL CILIATES, can Reproduce ASEXUALLY by Binary Fission and SEXUALLY by Conjugation. They also have TWO distinct kinds of NUCLEI (MULTINUCLEATE):

    A.  THE  LARGE MACRONUCLEUS CONTROLS ONGOING FUNCTIONS OF THE CELL (THE BRAIN) AND ASEXUAL REPRODUCTION. The Large Macronucleus contains Multiple Copies of DNA.

    B.  THE SMALLER MICRONUCLEUS IS INVOLVED IN GENETIC EXCHANGE DURING SEXUAL REPRODUCTION BY CONJUGATION - THE JOINING OF TWO OPPOSITE MATING STRAINS AND EXCHANGING GENETIC MATERIAL. Although Genetic Material is Exchanged during Conjugation, NO NEW Cells are produced. Following conjugation, each Paramecium divides, producing Four Genetically Identical Paramecia.  Exchange of Genes can enable organisms to adapt better to changing environments, the four Offspring are Genetically Different from Either Original Paramecium. 

PHYLUM ZOOMASTIGINA, ZOOFLAGELLATES

1. The 2,500 species that make up the Phylum Zoomastigna are characterized by the presence of one or more FLAGELLA, long, hairlike structures that are made up of Microtubules and are used for moving.

2. ZOOFLAGELLATES ARE PROTOZOANS THAT MOVE BY MEANS OF FLAGELLA.

3. Some Zooflagellates are free-living freshwater or marine organisms.

4. Many can live inside other organisms in SYMBIOTIC RELATIONSHIP (A relationship in which TWO Different Organisms live closely together; it can be either BENEFICIAL or HARMFUL to the Organism).

5. The Symbiotic Relationship may be:

    A. MUTUALISTIC RELATIONSHIP - Both Organisms Benefit.

    B. PARASITIC RELATIONSHIP - Causes Harm to the HOST.

6. Some Zooflagellates are parasitic organisms that cause Disease in Humans.

7. The Zooflagellate Trypanosoma causes African Trypanosomiasis, "African Sleeping Sickness", in Humans.  It produces Toxins that destroy red blood cells, causing the host to become weak.  This disease if left untreated eventually attacks the Host's Nervous System, causing DEATH.

8. This Disease effects all large Mammals, including Humans in some parts of Africa.  The Disease is spread by the BITE if the TSETSE FLY.

9. Another species called Trypanosoma cruzi, causes Chagas' Disease.  It is transmitted by an insect called the "Kissing Bug", patients suffer from fever, and heart damage.

10. The Trichonympha lives in the guts of termites, and help the termite digest Cellulose in wood. This is a mutualistic relationship, they both benefit from the relationship.

PHYLUM SPOROZOA, SPOROZOANS

1. All 6,00 species in the Phylum Sporozoa have adult forms with NO Means of Movement.

2. MOST SPOROZOANS ARE SPORE-FORMING PARASITIC (HARMFUL) PROTOZOANS.

3. The name Sporozoan comes from the fact that when they are immature, they are surrounded by THICK, SPORELIKE WALLS.

4. Adult Sporozoans have NO Structures for Movement.  Immature Sporozoans, called SPOROZOITES, can be transmitted through fluids from one host to another.

5. Sporozoans cause many Human Diseases, including MALARIA.  The Protozoan that causes Malaria is Named Plasmodium, and is transmitted by FEMALE Mosquitoes (Anopheles).

6.  The Life Cycle of the Plasmodium:

    A. Infected (Carrying SPOROZOITES) Female Anopheles mosquito bites a person.

    B. Plasmodium SPOROZOITES enter the bloodstream and travel to the Liver.

    C. They Divide Repeatedly, and NEW Spores called MEROZOITES emerge and infect Red Blood Cells

    D. Some Merozoites in the blood develop into special cells called GAMETOCYTES.

    E. When a female Anopheles bites the infected person, it ingests these Gametocytes.

    F. In the mosquito's Digestive System, the Sperm and Eggs combine to form a Zygote.

    G. The Zygote divides repeatedly to form more SPOROZOITES.

    H. The Sporozoites migrate to the salivary glands of the mosquito. When the insect bites another person, the Life Cycle Begins Again.

6. Malaria is a very serious disease characterized by severe chills, fever, sweating, fatigue, and great thirst.

7. One way to reduce human deaths (2.7 million annually) from Malaria is to control mosquito Populations.  Without the Mosquito host, the Plasmodium Protozoan CANNOT Complete their Life Cycle. 

8. Malaria is usually cured with a drug derived from the Cinchona Tree, which is native to the Americas called Quinine.