The Protozoans

11 A

The Protozoans

Pages. 256-262

by Emelyn Romero and Doina Monción

Protozoans

Protozoans means “first animals,” and organisms in this group are considered the most animal-like. In fact, some early microscopists believed that these “animalcules,” as Anton van Leeuwenhoek called them, gave rise to a larger animals, which in turn gave rise to even larger animals. From a Christian worldview , it is unreasonable to conclude that these organisms are the source of all animal life.

11.1

General Characteristics

Protozoans General Characteristics

Microscopic Unicellular (or ocasionally, colonial multicellular) organisms

Heterotrophic

Small size

Aquatic

and many live inside other organism. Some of these are parasitic, while others actually benefit their host organism.

Their small size helps protozoans in certain life functions.

Most protozoans are aquatic and are found in freshwater lakes,streams and ponds, as well as in oceans.Many others are found in soil where water is readily available.

are usually motile, able to move from place to place.

Protozoans General Characteristics

Most protozoans reproduce asexually by binary fission.

Eukaryotic

Can respond to changes in the environment

Some have areas of pigments called eyespots that can detect light intensity and either move toward or away from the light: others can detect and respond to chemical changes.

11.2

Protozoan Classification

Phylum Sarcodina: The Sarcodines

Phylum Sarcodina: The Sarcodines

• Are characterized by their lack of a standard body shape.

• When dormant, they may be nearly spherical. When moving or feeding , they will form a numerous extensions called pseudopodia that function as "false feet".

• Some species of sarcodines construct and inhabit shells. Sarcodines live in a variety of habitats, including fresh water, the sea floor,and the human mouth and intestines.

• Their mean of locomotion is amoebid movement.
• Examples: amoebas, radiolarians, foraminifers.
• Their means of nutrition are heterotrophic; some parasitic

Amoeba: A Typical Sarcodine

• Contractile vacuoles collect and eliminate water, regulating homeostasis between the amoeba and its environment.

• Amoeba proteus, the common amoeba, looks like little more than a blotch of gray jelly.

• The most outstanding feature of the amoeba is its amoeboid movement.

• When an amoeba moves, its endoplasmic streams toward one area of the cell membrane, causing a bulge to form. This bulge is gradually extended into a long pseudopodium. The cytoplasm of the amoeba flows into a pseudopodium and draws the cell membrane with it, causing the organism to move.

• Usually, amoebas are not swimmers but are part of the slimy covering of submerged rocks or plants.

• Like other sarcodines, amoebas do not form colonies.

• The cytoplasm in the amoeba is divided into two types: the endoplasm, located in the interior of the organism, and the clear ectoplasm, which is the outer portion next to the cell membrane.

• Reproduction: Asexual reproduction by binary fission .

+ info about amoeba

Phylum ciliophora: The ciliates

Phylum Ciliophora: The Ciliates

• The ciliates, members of the phylum Ciliophora, are among the most intricate and fascinating organisms in the kingdom Protista.

• These organisms may be up to 3 mm long, quite large for a protist, and exist in a variety of shapes.

• The characteristic that distinguishes this group is the possession of multiple hairlike projections called cilia.

• Their mean of locomotion is cilia.
• Examples: Paramecium, Stentor, Vorticella, Balantidium coli.
• Their means of nutrition are heterotrophic; some parasitic

• The smaller micronucleus functions during the exchange of genetic information during sexual reproduction.

Paramecium: A Typical Ciliate

• Protozoans of the genus Paramecium are common free-swimming inhabitants of stagnant lakes and ponds.

• The body of the paramecium as a funnel-shaped indentation called the oral groove. Cilia that line the oral groove sweep food material through the mouth pore into a short, blind tube called the gullet.

• Paramecia have a distinctive slipper shape that is maintained by the pellicle.

• Cilia completely cover the paramecium and can beat either forward or backward, enabling the organism to turn, rotate, and travel in any direction.

• The paramecium has two star-shaped contractile vacuoles.

• Reproduction: Asexual reproduction by binary fission and by a type of sexual reproduction called conjugation.

• The kidney-shaped macronucleus is the most conspicuous feature of the cytoplasm.

+ info

Phylum SPOROZOA: The SPOROZOANS

Phylum Sporozoa: The Sporozoans

• The members of the phylum Sporozoa are unique among protozoans since, as adults, they do not have pseudopodia, cilia, flagella, or any other special structures for locomotion.

• As the name implies, sporozoans form spores at some stage of their life cycle.

• All sporozoans are parasitic, often having complex life cycles involving a number of vectors and animal or human hosts.

• Reproduction: Asexual reproduction may occur by spore formation or by cell division. Many sporozoans also have some means of sexual reproduction.

• Mean of locomotion: none adults
• Examples: Plasmodium
• Their means of nutrition are heterotrophic; all parasitic

Plasmodium: A Typical Sporozoan

• Plasmodium, the genus that causes malaria, is probably the best-known representative of this phylum.

Malaria

Is caused by the anopheles mosquito

Disease and the Panama Canal

Phylum zoomastigina: The ZOOFLAGELLATES

Phylum Zoomastigina: The Zooflagellates

• The phylum Zoomastigina consists of the zooflagellates, protozoans that propel themselves by means of one or more flagella.

• Most of these organisms are unicellular and live in ponds and lakes, where they feed on smaller organisms by phagocytosis or haped absorb nutrients from decaying organic matter directly through their cell membranes. Other zooflagellates live inside other organisms and absorb nutrients from them.

• Their mean of locomotion is flagella.
• Examples: Trypanosoma, Giardia
• Their means of nutrition are heterotrophic; some parasitic

• Several human diseases that are caused by zooflagellates involve an insect vector One such disease, African sleeping sickness, or trypanosomiasis , is caused by members of the genus Trypanosoma.

• Reproduction: asexually by binary fission, but some do have a sexual life cycle also.

Interactions with man:

• Phylum Sarcodina: Although most sarcodines are nonpathogenic to humans, Entamoeba histolytica can cause a severe intestinal infection called amoebic dysentery.
• Phylum Ciliophora: The only ciliate that causes human disease is Balantidium coli. Balantiadiasis is an infection of the intestinal parasite, apparently rare,that infects pigs,horses,monkeys and wild rats.
• Phylum Sporozoa: Plasmodium is the genus that causes malaria.
• Phylum Zoomastigina: Trypanosoma causes African sleeping sickness or trypanosomiasis.

"But however secure and well-regulated civilized life may become, bacteria, Protozoa, Viruses, infected fleas, lice, ticks, mosquitoes, and bedbugs will always lurk in the shadows ready to pounce when neglect, poverty, famine, or war lets down the defenses."