Protozoa 

(Animal __ like Protists)

All protozoans are single cellular. Most of them ingest their food by endocytosis.

A summary of protozoan miscellany is given in the following table:


Common Name            From                         Locomotion               Examples

Zooflagellates          Unicellular, some colonial              One or more Flagella        Trypanosoma,Euglena,

Amoebae                    Unicellular, no definite shape        Pscudopods                         Amoeba, Entamoeba, 

Actinopods                Unicellular                                          Pscudopods                         Radiolarians     

Foraminifera            Unicellular                                          Pscudopods                         Forams

Apicomplexans        Unicellular                                          None                                     Plasmodium

Ciliates                         Unicellular                                          Cilia                                       ParForticella,                                                                                                                                                                                                  Stentoramccium, 

(A)  AMOEBAS

1. Habitat

This group incorporates all free-living freshwater, marine and soil amoebae, as well as those that are parasites of animals.

2.  Locomotion

Amoebae lack flagella and move by forming specialized cytoplasmic projections known as pseudopodia (false feet).


3. Food

Small micro-organism (paramecium, bacterium) and particles of organic matter. Food input (eating) is by phagocytosis.


It is by twofold fission or multiple fission.

Examples: Ammoeba proteus, Entamoeba histolytica, Giant Amoeba.

5. Cyst formation

During unfavourable conditions, they form a hard covering around their body known the cyst which allows them to withstand adverse conditions of long periods.

6.  As parasites

The internal parasite, Entamoeba histolytica, causes amoebic dysentery in humans.


GIANT AMOEBA (Pelomyxa palustris)

Body organization

The monstrous amoeba (pelomyxa palustris) may be the most primitive of all eukaryote-like forms.    

Habits and Habitat

This species has multiple membrane-bounded nuclei but none of the other organelles found in all other eukaryotes.


Methanogenic bacteria 

The giant amoebae obtain energy from methanogenic bacteria, these bacteria live inside the body of Fiant amoeba.
Giant amoebae inhabit mud at the bottom of freshwater ponds, where they contribute to the degradation of organic molecules.


(B)  ZOOFLAGELLATES

1. Unicellular or Colonial

These protists are usually single cellular (a few are colonial) organisms.


2. Form

These have spherical or elongated bodies with a single central nucleus.  


3.  Locomotion

They possess, one to many long, whip-like flagella that enable them to move. Flagellates move immediately, pulling themselves forward by lashing flexible flagella that are usually located at the anterior end.


4.  Habitat and Nature

They may be easy-living, symbionts or parasites.


5.  Nutrition

Flagellates get their food either by ingesting living or dead organisms or by absorbing nutrients from dead or decomposing natural issue.

6. Examples

i. Trichonymphas are complex, specialized flagellates with various flagella. They live as symbionts in the guts of termites & aid in the digestion of dry wood by creating an enzyme.


ii, Parasitic flagellates cause diseases;


For example

Trypanosoma is a human parasite causing African sleeping illness. It is transmitted by the bite of a contaminated fly. 

iii. Choanoflagellates


  • These are sessile marine or freshwater flagellates.
  • These are attached by a stalk, and a delicate collar, surrounding single Flagellum resembling collar cells in sponges (Phylum Porifera).

Examples:

    ➤1. Trypanosoma
    
    ➤2. Trychonymphas  


Trichonymphas



  • Trichonymphas are complicated and specialized flagellates. They persist as symbionts in the guts of termites. They assist termites in the digestion of dry wood.
  • They are not attached/bound by a stalk.
  • They have many flagella. The collar is absent.
  • They are not evolutionary valuable.


Trypanosoma



  • Choanoflagellates are sessile, maritime or freshwater flagellates.
  • They are attached by a stalk.
  • Their single flagellum is surrounded by a delicate collar.
  • They have striking similarities with the collar cells of the sponges. Thus these organisms are most imperative for the evolutionary point of view. It is understood that sponges have emerged from the Choanoflagellates.


(C) CILIATES

1. Pellicle

Ciliates are unicellular organisms with a flexible outer covering known pellicle that gives them a definite but changeable.


2. Cilia

The body is covered with several thousand fines, short, hair-like structures known as cilia. The cilia strike in such a coordinated way that the organism can not only go forward but backwards and tum around.


3. Locomotion

Some ciliates are sessile (e.g Stentor) and remain attached to a rock or other surface. Their cilia gear up water currents that draw food toward them.


4.  Nutrition

Most ciliates ingest bacteria or different tiny Protists.

5. Contractile Vacuole

Water regulation in freshwater ciliates is controlled by special organelles known contractile vacuoles.


6. Kinds of Nuclei

Ciliates differ from another protozoan in having two kinds of nuclei:


i) Micronucleus

Micronuclei are diploid, maybe one or more in number. They possess a cameo (role) in the sexual process.


ii) Macronucleus

A large, polyploid, macronucleus controls cell metabolism and growth.


7. Conjugation

Most ciliates are capable of a sexual process known as conjugation. During conjugation, two peoples come together and exchange genetic material.

Example:    Paramecium


8. Habitat

Ciliates are all aquatic. They may be free-living, parasitic or symbionts.


9. Examples: paramecium, Stentor



Ciliates

  • Ciliates possess cilia.
  • A pellicle is existing inside them. Consequently, they do not modify their shapes.
  • Ciliates possess two varieties of nuclei. These are diploid micronucleus and polyploidy macronucleus.
  • Most of the ciliates undergo conjugation during sexual reproduction.

Other protozoans

  • Cilia are not present in all other protozoans.
  • The pellicle is not present in different protozoans.
  • All other protozoans possess a single nucleus.
  • It is absent in all different protozoans.


D) FORAMINIEERANS AND ACTINOPODS

1. Habitat 

These marine protozoans create shells or tests


2. Shell or Tests

Tests of foraminifera are created of calcium whereas those of actinopods are made of silica.

3. Cytoplasmic projections

  • The shells or tests contain pores through which cytoplasm comes out.
  • These cytoplasmic projections from a sticky, interconnected net that entangles prey.


4. Grev Mud and chalk formation

Dead foraminiferans sink to the bottom of the ocean where their shells from grey mud that gradually transforms into the chalk.  Foraminifera of the past has created vast limestone stock.

5. Examples

Radiolarians, foraminiferans.


E) APICOMPLEXANS

1. Habitat

Apicomplexans from a large group of parasitic protozoa, some of which cause serious diseases such as malaria in human.


2. Locomotion

Apicomplexans lack specific structures for locomotion but the move by flexing.

3. Spore Formation

At some stage in their lives, they develop a spore that acts as a small infective agent transmitted to the next host.


4. More than one host 

Numerous Apicomplexans spend part of their life in one host and part in a different host species.

5. Example:      Plasmodium


6. The life cycle of Plasmodium



  • Plasmodium a malarial bloodsucker, is an apicomplexan. It gets into human blood via the bite of an infected female Anopheles mosquito.
  • Plasmodium first enters liver cells and then red blood cells, where it multiplies.
  • When each infected red blood cell bursts, several new parasites are released. The discharged parasites infect new red blood cells, and the process is repeated.
  • The simultaneous bursting of millions of red cells induces the symptoms of malaria; a chill followed by a high fever induced by harmful substances that are discharged and affect other organs of the body.