Protozoans
 
 
 
 

General Characteristics

Heterotroph
Most motile
Eukaryotes
Unicellular

This category can be broken down into four groups:
 
Group Phylum Name
Flagellates Mastigophora
Ciliates Ciliophora
Sporozoans Sporozoa
Rhizopods Sarcodina

Nutrition

    Protozoans hunt, digest and store food. Most are heterotrophs.  They feed on other animals to obtain the nutrients they need to live.

Movement

    Protozoans move by the use of cilia, flagella, pseudopods or some have no movement (Sporozoa).

Defense

    When too much water collects in the cell, the vacuole move to the outer surface of the cell and squeezes out the water. This stops the cell from swelling up and bursting.

Reproduction

    Asexual reproduction of protozoans occurs when the cell divides in half by binary fission.  Some which are parasites multiply within the host.  Some protozoans reproduce sexually as well.  This can happen when two protozoans carrying half of their regular genetic material fuse together and form a new cell.  Others exchange genetic material during mating.

Respiration

     Respiration takes place when oxygen diffuses into the cell, where the food molecules become oxidized.  The energy produced and the organic molecules are used for maintenance and building of the cell.  Waste products ,carbon dioxide and water diffuse out of the cell.

Excretion

    Waste materials in protozoans are removed from the cell by diffusion through the cell.  They are transported  out of the cell by food vacuoles that come in contact with the surface.  This is known as exocytosis.
 
 
 




Rhizopods
 

General Characteristics

  motile (pseudopod)
  eukaryote
  heterotroph

Taxonomic Breakdown
 
Kingdom Protista
Phylum Sarcodina

 

Nutrition

    They engulf their food with their pseudopods where it then forms a food vacuole. This is where the food is broken down and spread throughout the rhizopod. This process is called phagocytosis.
 

Movement

    They move with the use of their pseudopods.

Reproduction

    Amoebas, under favorable conditions, reproduce by binary fission (This means dividing in two), producing two daughter amoebas. The nucleus divides by mitosis.  If ameobas are divided artificially the nucleus does not divide.  Only the half of the amoeba containing the nucleus survives while the other half dies.  If conditions are unfavorable the amoeba will secrete a protective covering and wait until conditions are favorable to divide.

Excretion

    Materials that are useless to the amoeba are held in the food vacuole until the vacuole comes in contact with the membrane of the body surface. This is where the waste is expelled from the body

Respiration

    Respiration takes place by diffusion of gases through the cell membrane

Defense

    The Arcella, known as a domed Amoeba, builds a transparent dome from whatever building materials it can find in the pond, usually sand. It then encloses itself in the dome for protection.

Economic Importance

    The skeletons of Foramininfera make up much of the limestone and chalk on the Earth.

Examples of Rhizopods

Amoeba proteus (common amoeba)
Entamoeba histolytica (causes amoebic dysentery)
Radiolarians (internal glass-like skeletons)
Foraminifera (large shelled amoeboid belonging to Sarcodina)
 
 

To see images of Rhizopods Click Here
 
 
 
 
 
 



Ciliates

General Characteristics

Motile (cilia)
Eukaryotes
Heterotroph

Taxonomic Breakdown
 
 
Kingdom Protista
Phylum Ciliophora

Method of movement

    It swims rapidly by coordinated wavelike beats of its many cilia.  A paramecium normally moves forward in a corkscrew fashion but is capable of reversing direction when it encounters undesirable conditions.

Reproduction

    The larger nucleus is thought to regulate cell functions, while the smaller nucleus is involved in reproduction.  Ciliates usually reproduce asexually by binary fission. Sometimes they reproduce sexually. This takes place when two individual ciliates join together at the oral grooves and exchange portions of the micronuclei. After this stage each individual divides.

Nutrition

    At one side of the ciliates body there is a mouth like opening called the oral groove. The food is swept into the oral groove by the cilia.  Food consists of other protozoans, bacteria and algae.

Excretion

    Undigested food is discarded through the anal pore (which is some distance behind the oral groove).  Metabolic wastes diffuse out directly at the body surface.

Respiration

    Respiration of Ciliates can be anaerobic (occurring without oxygen) or aerobic (requiring oxygen).  Anaerobic protozoa must live without oxygen and will die if exposed to it.  Respiration rate varies directly with temperature and also depends on the kind of molecules broken down for energy.   It also varies with species.
 

Defense

    In many ciliates there is a layer of many tiny carrot shaped bodies, called Trichocysts, underneath the pellicle.  When discharged each Trichocysts forms a long sticky thread.  Usually they are discharged as a means of defense but are sometimes used as an anchor.

Examples of Ciliates

Paramecuim (Paramecium caudatum)
Stentor (Stentor coeruleus)
 

To see images of Ciliates click here.
 
 
 




Sporozoa

General Characteristics

Not Motile
Hetertrophic
Eukaryote

Taxonomic Breakdown
 
 
Kingdom Protista
Phylum Sporozoa

Method of Movement

    Sporozoans have no physical form of movement. However, they can be moved by the currents of the blood or other fliuds of their hosts.
 

Reproduction

    They reproduce sexually in one host and then asexually in a second host.

Nutrition

     They are parasites.  Sporozoans have special organelles that allow it to invade a host cell.

Defense

    The Plasmodium vivax(Sporozoan) tucks inside the red blood cells, where the parasites are protected from attack by the antibodies of the host. Even when they leave to invade fresh cells, they evade immune destruction by constantly changing their antigens [any of several subsatnces that cause the development of antibodies].

Examples of Sporozoans

Plasmodium vivax (Causes Malaria)
Monocystis agilis
 
 

To see images of Sporozoans, click here
 

                                                                                               



Flagellates

General Characteristics

Motile
Unicellular
Heterotroph
Eukaryote

Taxonomic Breakdown
 
 
Kingdom Protista
Phylum Mastigophora

Method of movement

They move with the use of Flagella an example is a Trypanosome

Nutrition

They get their nutrients by eating other organisms or by absorbing food molecules through cell membranes.

Defense

Members of the Trypanosoma Genus releases a poisonous substance that attacks the nervous system, causing weakness and eventually death ( African Sleeping Sickness).

Excretion

Undigested wastes leave trough the anal pore. Contractile vacuoles are used in pumping water out of the cell.

Economic Importance

Flagellates are the primary component in the marine food chain
 

Examples of Flagellates

Trypanosoma gambiense (sleeping sickness)
Trichonympha
 

To see images of Flagellates, click here.
 




Interesting Facts
 

* Sporozoa are the only animal like protist that had no form of movement.

* The plasmodium (Sporozoan) causes malaria.

* Sporozoa need both a human or other vertebrate and a mosquito to complete their life cycle.

* Phylum Sarcodina (Rhizopods) are the largest phylum of protozoans.  There are about 18,000 known species of Rhizopods.

* Some Amoebas (Rhizopods) are harmless, while others cause serious disease (Entamoeba histolytica)

* Amoebas are constantly changing their shape.

* Some amoebas  are as small as 0.25mm in length while others can be up to 8mm.

* Pseudopods may be rounded at the tip (lobopodia), pointed (filopodia), branched and fused together (rhizopodia) or somewhat rigid and pointed (axopodia)

* Paramecia can divide as often as two or three times a day.
 

* Ciliates have a skeleton like covering made of Polysaccharides.



 

Test your knowledge of Protozoans  Click Here

 

Links
http://silkentent.com/gus1911/RonPond.htm
http://kids.infoplease.lycos.com/encyclopedia.html
http://library.thinkquest.org/27819/cgi-bin/quiz.cgi?quiz=7_8
http://home.istar.ca/~smhaley
 
 

Bibliography