BIO 002: INVERTEBRATE BIOLOGY PHYLUM PROTOZOA

PHYLUM PROTOZOA

Protozoa refers to single-celled eukaryotic organisms, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. The name protozoa means “first animals” and has been derived from two Greek words, PROTOS, meaning first and ZOON, meaning animal. They are looked upon as the most primitive form of life, appearing first in the evolutionary history. They range in size from 1 to 106 micrometers.

Structurally a protozoan is a one-called animal comparable with one cell or a METAZOAN with a body consisting of only a mass of protoplasm. But functionally, it is an entire organisms, physiologically balanced and performs all the essential process of an animal, hence protozoans are called acellular or non-cellular organisms.

Historically, the protozoa were regarded as "one-celled animals," because they often possess animal-like behaviors, such as motility and predation, and lack a cell wall, as found in plants and many algae. There are 30,000 to 40,000 known species of Protozoa. However, the actual number of species is probably much larger, since the organisms have not been thoroughly investigated owing to their microscopic size and to technical difficulties. Hundreds of new species are being discovered each year. Although the traditional practice of grouping protozoans with animals is no longer considered valid, the term continues to be used in a loose way to identify single-celled organisms that can move independently and feed by heterotrophy.

Characteristics of Protozoa

 They move through the aid of Locomotry organs like hair-like Cilia e.g. Paramecium, finger – like pseudopodia e.g. Amoeba or whip-like Flagella e.g. Euglena or locomotory organ may be absent.  The presence of moisture in their environment is an essential condition for their mode of life.  The mode of life could be free-living or parasitic.  Respiration occurs through general surface of the body.  Excretion occurs through general surface or through contractile vacoules which also serve for Osmo-regution.  Nutrition may be holozoic (animal-like), holophytic (Plant-like), Saprophytic or parasitic.  Reproduction takes place asexually by binary or multiple fission and budding, and sexually by conjugation of the adults or female gametes.  Encystement commonly occurs to help in passing unfavourable condition and it also helps in dispersal.  Body is either naked or covered by a pellicle (plasmalemma or theca or lorica)  Life cycle often exhibits alternation of generation, i.e. it includes asexual and sexual phases.

Classification of Protozoan

On the basis of locomotory organelles, phylum Protozoa can be divided into the following four classes.

Class: Flagellata or Mastigophora

(1) The body is covered by a thin pellicle or cuticle which provides a definite shape.

(2) The locomotory organs are flagella. It can also be used for food capturing or attachment or protection.

(3) The contractile vacuoles are present in fresh water forms with accessory vacuoles. (4) Chloroplasts are found in some forms (e.g. Euglena).

(5) They may be free living or parasitic.

(6)The class flagellata has been divided into eight orders. They are as Chrysomonadina, Cryptomonadina, Euglenoidea, Phytomonadina, Dinoflagellata, Cystoflagellata, Protomonadina and Polymastigina

(7) Examples: Chrysamoeba, Cryptomonas, Euglena, Volvox, Chlamydomonas, Noctiluca, Mastigamoeba, Monal, Bado, Trypanosoma, Leishmania, Proterospongia etc.

Class: Rhizopoda or Sarcodina

1) Free living or endoparasite.

2) Contractile vacuole may be present or absent.

3) Locomotory organelles are pseudopodia which also help in food capturing.

4) Body is without a pellicle, and has no fixed shape.

5) Protoplasm is differentiated into ectoplasm and endoplasm.

6) Single nucleus is found in the endoplasm.

7) Nutrition is holozoic and parasitic in few forms.

8) Reproduction takes place by fission

9) Examples include: Amoeba, Entamoeba etc.

Class: Spoprozoa

1) They are exclusively endoparasites. 2) Locomotory organelles are absent. 3) Body is covered by a thick pellicle.

4) Nutrition is saprophytic and contractile vacuole is absent. 5) Sexual reproduction takes place by gamete or spore formation. 6) Examples include: Monocystis, Plasmodium etc. Class: Ciliata

1) They may be either free living or endoparasite. 2) Nucleus may be one, two or many in number.

3) Body organization is complex.

4) Body shape and size is definite and is covered with a pellicle.

5) Cilia are the locomotory organelles. 6) They have a holozoic mode of nutrition.

7) Small micronucleus is reproductive in function whereas large macronucleus is vegetative in function. 8) Asexual reproduction occurs by transverse fission and sexual by conjugation. 9) Examples include: Opalina, Nyctotherus, Balantidium, Paramecium etc.

AMOEBA

Phylum - Protozoa

Subphylum - Plasmodroma

Class - Rhizopods

Order - Lobosa

Genus – Amoeba

Specie – Amoeba Proteus

Diagram of an Amoeba

Morphology

Structure of Amoeba

Amoeba, a member of class Sarcodine, is one of the most common example of the simplest animal life on earth. The most common species is Amoeba Proteus. It measures about 0.25 to 0.60mm in size and is difficult to see without the aid of a microscope. It appears as a minute-slate coloured shinning, irregular mass of a gelatin-like substance with sturdy looking fine particles. It consists of a very- thing elastic external plasma membrane or plasmallema. It has an irregular shape due to the fact that it forms protrusions of its body surface facing different directions (Pseudopodia) and they are constantly changing in shape and direction.

Habitat

Amoeba Proteus can be found in a variety of habitats where conditions (temperature, organic food and water) are favourable. E.g of such locations are: bottom of ponds, debris from watering troughs, pools, drains, ditches, abandoned tanning pits etc and wherever there is abundant aquatic vegetation.

Locomotion

Amoeba moves from place to place by means of their Pseudopods (false foot). Pseudopods are flowing projections of cytoplasm that extend and pull the amoeba forward or engulf food particles. An amoeba projects a pseudopod forward and flows into it thereby achieving locomotion.

Food and Feeding

The aquatic environment of amoeba has tiny particles of various organic substances, suitable for food. This includes unicellular plants, particular bacteria and diatoms, tiny filaments of algae, various protozoan species together with organic debris of many kinds. It is holozoic in nutrition, that is, it ingests solid organic particle. This is with the aid of the pseudopodia. This it does by projecting the pseudopodia and engulfing the food particle.

Excretion

There is no specialized organelle in amoeba for throwing out the waste or indigestible material. These waste materials leaves the animal through a temporary opening in the ectoplasm at the rear of the animal. The plasmallema ruptures at this point of contact with the vacuole and the feaces are egested or left behind as the animal flows away. New plasmalemma is formed at the ruptured area to stop the outflow of endoplasm.

Respiration

The process whereby oxygen entering the protoplasm is exchanged for CO2 leaving it is known as Respiration. In amoeba this exchange is carried out mainly through the general body surface of the organism. The water in which amoeba lives must contain dissolved oxygen in order that this diffusion may go on.

Osmoregulation

Osmoregulation refers to the regulation of water content. The contractile vacuole is responsible for this function. The contractile vacuole is a clear space. It contains a fluid less dense than the surrounding protoplasm. At more or less regular intervals, it suddenly collapses, its walls having contracted, force out the fluid contents which is known to contain traces of urea and Carbon dioxide but mostly water.

Reproduction

Reproduction in amoeba is asexual and is by the following methods: i. Binary Fission ii Sporulation iii. Encystment