In this article we will discuss around Protozoa:- 1. Habitat of Protozoa 2. Design of Protozoa 3. Organelles.

Habitat of Protozoa:

Adaptation of Protozoa is ex­tended come all settings open to micro­organism. Free-living creates occur in fresh water lakes, ponds, open up ocean, river and also even in momentary pools. Soil and sands also form natural atmosphere for countless Protozoa.

Such Protozoa live in the movie of mois­ture surrounding soil particles or sand grains. Parasite protozoa occur in numerous different types of animals, in specific plants and even in a couple of protozoans themselves. The microsporidian Nosema notabilis is a hyperparasite ~ above myxosporidian Spherospora (Fig. 10.52).


In the body of the animal host they occur in the coelom, digestive tract, individual organization cells and body fluids. Trypanosomes live in the blood plasma and malarial para­sites invade individual red blood cells and also liver parenchyma cells and also ultimately ruin them.

Certain parasitic develops stick to a single kind of organize while there are others which can live effectively in a couple of closely related types of animals, or 2 or much more different and unrelated species of hosts. Because that such Protozoa that have the right to invade unrelated hold spe­cies, a readjust of master is essential for the completion of that life cycle.

Of every the ani­mals, people are most hospitable to parasitic protozoa for as numerous as twenty five different species of parasitic Protozoa have actually been encountered in them.


The specific variety of different kinds of Protozoa living today is a matter of speculation. It has actually been estimated that there are around 30,000 species. Yet this estimate is topic to inaccuracy as plenty of current name of species represent duplication.

Protozoa or Protista:

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All the varieties of nutrition, e.g., holozoic, saprozoic and also holophytic room seen in the protozoan group. Flagellates prefer Euglena, save on computer chlo­rophyll and also carry top top photosynthesis favor plants. Mycetozoa of protozoologists is the various other name that slime molds the botanists (Fig. 10.53).

That method they are an ext plant-like 보다 animal-like and as a an outcome the plain criteria because that separating tree from animals breakdown at the level that Protozoa. To avoid unwanted disagreements in instance of those animals stamped through such mixture of personalities some influenced Biolo­gists have proposed a group, Protista, to include Protozoa, imreparable cells algae and also other micro-organisms.


Theoretically the plan has plenty of ad­vantages however in practice the ax protista has not been adopted because that proprietary interests of Botanists in Algae, Bacteriologists in Bacteria and Zoologists in Protozoa.

Architecture that Protozoa:

(i) Shape:

Excepting a few Rhizopods most Protozoa are with fixed shape and also size char­acteristic for each species. The creates of Pro­tozoa may be flattened, spherical, oval or elongated and also often bizzare shapes are likewise encountered. Though majority of Protozoa exhibit critical bilaterial symmetry, all species of animal-symmetry space witnessed in them.

Rhizopods and Foraminifera room asym­metrical. Heliozoa and Radiolarians exhibition spherical symmetry if radial the opposite is provided in sessile choanoflagellates, bilateral the opposite is noticeable in Giardia or Octomitus.

(ii) Size:

Most that the Protozoa space micro­scopic in size and selection from 2-4µ to numerous millimeter in size or diameter. Plasmodium residing in ~ the RBC is taken into consideration as the smallest of every Protozoa. Radiolaria and also Foraminifera are largest in size among the Protozoans. The shells the Foraminifera may achieve a diameter of 2-15 mm. Spirostomum ambiguum is the largest among freshwater ciliates and also is around 4.5 mm in length.

(iii) The cell Body:

The simple and the fundamental component of the Protozoan body is protoplasm i beg your pardon is distinguished into nucleus, cytoplasm and also cell membrane.

A. Nucleus:

The form, structure and also size that Protozoan cell nucleus are incredibly vari­able (Fig. 10.54). Many Protozoa save on computer a solitary nucleus and in numerous there room two or more. Giardia and Protoopalina save two similar and similar nuclei while Euciliates and Suctoria be afflicted with dissimilar nuclei, i.e., micronucleus and also macronucleus. This nuclear dimorphism is additionally present in specific foraminifera.

The macronucleus is consid­ered as ‘somatic or vegetative’ cell nucleus per­forming general metabolic activities while the little one is thought about as ‘generative’ i beg your pardon looks ~ the reproductive part. In Pelomyxa, Opalina, Myxosporidia and Microsporidia there are numerous similar nuclei.

The macronu­cleus uses variation in its form and struc­ture. The is compact, spherical or ellipsoidal in many cases. In Vorticella it is lot elongated. In Spirostomum and also Stentor, that is prefer a chain the nodes joined to one another by filaments. The dyed of the meganucleus is called trophochromatin while that of micronucleus is consisted of of idiochromatin.


Protozoan nucleus might be vesicular or compact. Vesicular nucleus is composed of a nu­clear membrane i beg your pardon is an extremely thin and also deli­cate yet nucleoplasm is distinct and chroma­tin content is less. The compact nuclei are constantly massive together they contain huge amount of dyed substance and also a comparatively small amount that nucleoplasm. The macronu­cleus that ciliates is that compact type.

Within the cell core there space two general kinds of nucleolus-like bodies which save no DNA and are referred to as ‘endosomes’ or nucleoli. The endosome in Euglenoids is cen­trally located, comprised of 3 concentric zones and divides during nuclear division.

In parasitic amoebae prefer Entamoeba the endosome is written of a number of ir­regular masses, every containing numerous little particles and also it disappears throughout mitosis.

Repeated mitosis in the nucleus through no resolution of atom membrane result in some situations in the formation of a polyenergid nucleus. Every polyenergid nucleus bears plenty of sets the chromosomes which are finally distributed to the daughter cells. Polyenergic states are thought to it is in antithesis of sporulation.

B. Cytoplasm:

It is the extra-nuclear part of the Protozoan body. The cytoplasm is colourless, homogeneous, and also in optical monitoring presents granulated, vacuolated, reticulated or fibrillar texture. The cytoplasm is identified into ectoplasm and endoplasm. The ectoplasm is likewise called the ‘Cor­tex’.

The cortex is hyaline and also gelatinous and also may be defined as a part of cytoplasm bounded externally by plasma membrane and internally through endoplasm. In Ciliophora, the cortex houses a number of organelles. The endoplasm is voluminous and also fluid (Plasmasol).

C. Cell Surface:

The cytoplasm bears a protective envelope which may be current in the complying with textures:

1. Plasmalemma:

An extremely thin membrane i m sorry regulates the entry and also exit of materials between the organism and also the surrounding medium in which it lives.

2. Pellicle:

The surface layer i do not care gelated and also forms a clearly shows firm pellicle. The pellicle is living and is frequently sculptured together in Paramoecium.

3. Cuticle:

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The outer limiting surface may be a cuticle as in Monocystis. The cuticle is dead and may be made up of nitrogenous elements, carbohydrate or cellulose.

4. Shell:

The entirety body might be encased in a close installation shell having actually an aperture v which protoplasm may be extruded. The shell is written of nitrogenous ele­ments in Arcella, the silicious bowl in Euglypha or calcium lead carbonate as in Foraminifera. Cysts space temporary shells with no opening.

D. Cytoplasmic Inclusions:

1. Save on computer food:

Polysaccharides, lipids and also rarely nitrogenous products remain installed in the cytoplasm. Polysaccharides are existing in the kind of starch granules, leucosin and also paramylum bodies together in Stentor and cysts that Entamoeba. The synthetic of polysaccharides in Phytomastigophores is in­dependent the the visibility of chlorophyll.

Presence of glycogen has actually been report in any Sarcodina and Ciliates. In some para­sitic protozoa glycogen synthetic is stepped up during cyst formation. This glycogen space never similar with the glycogens that other higher animals. A peculiar type of glycogen i beg your pardon is neither usual glycogen no one true starch is encountered in the endoskeletal key of specific ciliates i m sorry live in the rumen of cattle.

Histochemical test have displayed that carbohydrate is stored by Amoeba in the form of glycogen. Washed amoeba, if treated through radioactive glucose, the isotope is recovered native the Amoebic glycogen.


Lipids, i.e., fat and also other associated sub­stances, continue to be stored and distributed throughout the cytoplasm as tiny globules or in some instances they continue to be localised in a particular area the the body. This save oil in some Phytomastigophora presents a disagree­able taste and also colour.

Nitrogenous reserves together chromatoid bod­ies that Entamoeba are likewise recognised. They space seen in the cysts, and also the characteristic forms of chromatoid aid in differentiating one types from the other. The chromatoid bodies are consisted of of protein and also RNA, and till date their duty is unknown. ‘Volutin granules’ include RNA have actually been reported in numerous Protozoa.

2. Mitochondria:

Mitochondria are present in every aerobic species. Variety of mitochondria present in one organism space dependent ~ above the volume of that specific organism. In Tetrahymena over there are countless mitochondria if in avian malarial para­site Plasmodium lophurae there are one or 2 mitochondria.

Structurally and functionally the Protozoan mitochondria differ very small from that of higher animals. The mitochon­dria take place as little spherical, oval, rod-shaped or filamentous bodies. They may be evenly dispersed in the cytoplasm or may be local­ised in place as they space arranged between the kinetostomes of cillia in Opalina and also Paramocium.

3. Golgi apparatus:

Presence that Golgi body in the form of compact, flattened and plate-like vesicles has been report in Amoeba and Pelomyxa through certainty.

4. Cytoplasmic pigments:

Pigment gran­ules of various colours—violet, blue, green, yellow, pink, red occur in the cytoplasm of phytoflagellates and ciliates, Red pigments occur in Phytomonadina and Euglena. As soon as exposed come bright light this red pigments rise in number and also mask the usual eco-friendly colour the the animals. The pink pigments of Blepherisma undulans is toxic to other ciliates.

Organelles in Protozoa:

A. Vacuoles:

Several type of vacuoles occur in differ­ent protozoa.

1. Contractile vacuoles:


An intracellular, tiny incon­spicuous, membrane bound, spherical, fluid filled vesicle that maintains the osmoregulation in some protozoans.


They are mainly discovered in freshwater protozoans such together sarcodines, flagellates and ciliates. The is also found in some marine forms however totally absent in parasitic creates such together Sporozoa.


The position, number and ac­cessory frameworks of the contractile secret are different in various Protozoa (Fig. 10.56). In Amoeba, the place of the vacuole transforms with the motion of the organism. In ciliates and also flagellates the place is an ext or less fixed.

In numerous Heliozoans contractile vacuoles take place in the ectoplasm. In Balantidium and also Nyctotherus the contractile vacuole is positioned close to the cytopyge. Deep sit contractile vacuoles room often listed with a vulnerable duct i m sorry connects the vacuole v the spicy on the pellicle as in paramoecium woodruffi.



The variety of vacuoles different in different groups of protozoa but remains constant in a particulaar species. It is single in Amoeba and also Euglena yet two in paramoecium.


The contractile vacuoles are gen­erally sherical in shape, and simplest spheri­cal form is uncovered in Amoeba yet in plenty of ciliates castle have come to be star-shaped (e.g., Paramoecium) due to the fact that of a number of collect­ing canals (5-12) which radiate indigenous the key vacuole (Fig. 10.39).

Each canal is composed of a small elongated terminal part, a swelling ampulla and also a quick injector canal which opens into the vacuole (Fig. 10.40). In flagellates like Euglena, the contractile vacuole is more complicated and a number of small acces­sory vacuoles are located about the main contractile vacuole.


The contractile vacuole complex consists the a contractile vacuole proper and also a device of vesicles and tubules referred to as the spongiome (Fig, 10.57) which lies in between the mitochondria and plasmalemma and helps in collection of fluid from the bordering cytoplasm and transfers into the contractile vacuole.

A discharge sharp is situ­ated in the plasmalemma with which water expels to the outside. The diameter of motor is about 1 µm. The breadth that the boundary membrane of the vacuole is around 0.5 µm. The volume the vesicles different from 20 nm to 100 nm. Little fluid-filled vesicles save polyribsomes. Rough walled motor are comparable in structure to E.R. That mammals.


Types of contractile vacuoles:

The con­tractile vacuoles may be following form on the basis of intricacy of the spongiome:

(i) In the very first kind only collecting tubules are current in the spongiome and col­lecting fluid is expelled out v the pore of the plasmalemma (Fig. 10.57).

(ii) In the second kind, the tubules and also vesicles are present in the formation of spongiome and the tubules collect fluid from the cytoplasm. The liquid is trans­ferred come the long-term collecting ca­nal which is dilated to form ampulla. The over mentioned two species are discovered in ciliates (Fig. 10.57).

(iii) In the third form a long-term pore is lacking and also vacuoles are developed by the blend of tiny fluid fill vesicles. The vacuoles are disappeared after the discharge that solutes (e.g., Amoeba).

(iv) In the fourth type the vacuole is filled by the conspicuous ampullae and also through a permanent pore the liquid is expelled out. The ampullae, irreversible pores and bundle that microtubules are absent in the 3rd and fourth types.

Formation that the contractile vacuole:

All the contractile secret pass through a cycle. The beginning of a brand-new vacuole requires the fusion of many small vacuoles in the cytoplasm.

The young vacuoles thrive in vol­ume (diastole) by combination of other little vacuoles or by receiving contribution of fluids from clearly shows canals. As soon as the volume get its preferably the components are discharged come the outside (systole) v the pores in the pellicle or into the gullet (Fig. 10.56).

Functions the contractile vacuole:

(i) Osmoregulation:

All freshwater protozoa solve the con­stant osmotic difficulty with the assist of the contractile vacuoles. The plasma­-lemma in this organisms is semiper­meable.

And as the concentration the water in the cytoplasm is reduced than the of the surrounding medium a con­stant circulation of water right into the pet body occurs. Water passes much more rap­idly into the body than it leaves. The organisms eliminate these excess wa­ter by pump them out v the help of contractile vacuoles and prevent the body from being waterlogged.

(ii) Excretion:

(a) part amount of nitrogenous wastes space voided along with the discharged water.

(b) Ludwing confirms the the con­tractile vacuole not only regulates the osmotic pressure but likewise helps in the excretion the CO2.

(iii) that is thought about by the differences in pulsation frequency the contractile vacuole is largely excretory in maritime protozoa, however excretory and osmotic pressure regulate in freshwater protozoans.

2. Food vacuoles:

They space temporary vacuoles and also are universally present in holozoic Protozoan which take it in whole or parts of various other organ­ism. In creates which carry out not have a cytostome the food vacuoles assume the form of the food. The food vacuoles space spherical in develops with cytostome.

A number of food vacuoles might remain present at a time and also they con­tain food corpuscle at different stages that di­gestion. Food secret in ciliates show a circulatory motion or cyclosis within the endoplasm. Food secret are absent in saprozoic protozoan.

3. Sensory secret or Concretion vacuoles:

Certain parasitic ciliates of the households Butschliidae and also Paraisotrichidae have actually a number of vacuoles situated in the anterior an ar of the body under a pellicular cap. The vacuolar cavity includes a variety of granules, referred to as statoliths and also a number of fibrils sign up with the vacuole v the pellicle. These vacuoles are thought about as statocysts and excretory vacuoles.

4. Superficial vacuoles:

Superficial vacuoles are uncovered in passively floating Sarcodina which have a foamy external cytoplasm. These thin-walled vacuoles pre­sumably comprise a irradiate weight liquid or gas maintain the organism at a specific depth. Once the vacuoles collapse, the ani­mal sinks. When brand-new vacuoles develop, the biology rises. For this reason the superficial vacuoles assist in floatation.

B. Mouth and also Associated Or­ganelle:

Amoeboid organisms feed on bacteria or other small organisms and also the gulp down of the food particle requires the development of a food-cup to enclose the food or the forma­tion of a gullet-like structure.

In couple of phagotrophic ciliates and also flagellates a gullet is formed throughout ingestion and also persists dur­ing the energetic life that the organisms. Particular euglenoid flagellates own an accessory rod-like device which help in punctur­ing the body wall surface of the host too large to engulf whole. Both the food cup and also gullet room extra-temporary structures.

Permanent and also specialised feeding organelles dubbed cytostome is encountered in ciliates prefer Paramoecium and also Tetrahymena (Fig. 10.58). In Tetrahymena, there are three membranelles in the roof of the mouth and also a membrane along the left margin. A membranella is written of a double cili­ary lamella fused to form plate. The mem­brane is thin, transparent and also bears one or 2 rows of cilia fused together.

The mem­brane is bigger in Tetrahymena contrasted to other ciliates. In Hypotrichias the membranelles are an extremely well occurred but the mem­brane is ill developed. In ciliates the various stages the specialisation the the cytopharynx indigenous an humble start to a facility end are easily recognisable.

In suctorians the tentacles beat the function of the gullet. They feeding on various other ciliates which sometimes encompass an organism plenty of times larger than chin (Fig. 10.58).

The tentacles adhere round the prey and it can hold an organism countless times larger than it. Soon after adhesion the protoplasm the the recorded ciliate beginning flowing ring the tentacle come the base whereby a food vacuole develops. The lining the the Suctorian tentacle is con­tractile and also there is some sort of peristaltic action.


C. Cytopyge or cell Anus:

The indigestible residue of food in instance of the ciliates is thrown out v a particu­lar spot, called cytopyge or cabinet anus (also dubbed cytoproct). That lies in ~ the posterior ven­tral side of the body. The clues is recognisable as soon as excrement is actually being cast away. This is again a temporary structure. In Nyctotherus a permanent cytopyge is seen.

D. Chromatophores, Pyrenoids and also Stigma:

Chromatophores, i.e. Chloroplastid and some non-green oribelles are limited to plant-like flagellates. The chromatophores occur in discoid, ovoid, band-like, rod-like or cup-like forms. In Chlamydomonas a single cup-shaped chromatophore is found and it is taken into consideration as a primitive form. This cup may be subdivided into pairs that lateral lobes or also to different lobes.

Some the the Euglenidae contain plenty of flattened chromatophores arranged near the surface ar of the body. In Peridinium chromatophores are arranged near the surface of the human body and kind anastomo­sing network. Electron micrograph studies have actually revealed that chromatophores room dou­ble membranes and also have a lamellar framework in i beg your pardon electron opaque layers alternate with electron transparent layers.

Electron opaque are thought to be laden through photosynthetic pigments. Chlorophyll is the many predomi­nant colours in the chromatophores however there are other pigments present in far-ranging amounts.

These pigments space greenish yel­low, yellow red, brown and even blue and when existing in superabundance they mask the eco-friendly chlorophyll. The cytoplasmic pink pigment of Blepherisma is toxic to several other ciliates and also to small metazoons. Also the annelid worm, Dero is vulnerable to it. As soon as exposed to an extremely bright light, Blepherisma drops a victim that its very own pigment or a toxicity product that the pigment.

Pyrenoids space structures which usually remain associated with the chromatophores though all chromatophores bearing flagellates execute not own them. The framework of the pyrenoids varies from solid body to aggre­gate that granules. In Euglena the pyrenoid is encased in a great of paramylum when in Chlaydomonas the is often surrounded by starch granules.

From this close structural relationship it is argued that pyrenoids are functionally connected in the synthetic of starch and also other polysaccharides. However, there must be other machinery for the syn­thesis of these substances as there are certain flagellates there is no pyrenoid, which have the right to synthesise together polysaccharides.

Stigma or eye-spot occurs in many chlo­rophyll bearing and also a few colourless flagel­lates. The stigma consists of reddish colors presumed to be carotenoid. The stigma the Euglena shows a mass of reddish granules installed in a matrix. It is a discoid body, placed close to the gullet.

The flagellum which occurs from the base of the reservoir v the gullet bears a tiny granule or a paraflagellar human body at the level that the stigma. In Volvox and also related colonial varieties the stigma is comprised of a concave mass of pigments and a hyaline lens.

The duty of the stigma is to help in the orientation of the flagellates towards a suitable light source. From the work on Euglena it is assumed that the parabasal human body of the flagellum is a light perceptible structure and also it becomes created by the light energy which the stigma absorbs.

E. Neuromotor Organelle:

A well-defined system of nerves is lack­ing in the protozoan. However it has been checked out that the cilia that the ciliates are qualified of make a well co-ordinated movement. It is known that the ciliary co-ordination is due to the visibility of details fibrillar mechanism in Epidinium. The existence of a neuromotor device in the system of Epidinium is ad­vocated.

This apparatus is composed of a main motor mass, referred to as the Motorium, situated in the ectoplasm, and from it definite strands radiate to the root of the membranellae, cytopharynx and other structures.

Similar apparatus has actually been it was observed in Balantidium, Paramoecium and also many various other ciliates. Klein (1926) by silver-impregnation method has prove the existence of together radiat­ing fibrils and also has designated the fibres as silver lines and the whole complicated as silver line system.

F. Safety or supporting Organelles:

1. Pellicle:

Outside the plasma membrane many protozoa have actually a differentiated pelli­cle, i.e., a continuous covering which might be an ext or much less flexible. The special pellicles often show surface decorations in the type of ridges, papillae or pits.

The pellicle in ciliates is perforated v which cilia and trichocysts emerge. The chief component of pellicle in instance of Amoeba is polysaccharide and in Euglena the major component is protein.

2. Exoskeleton:

Instead of a pellicle or in addition to a pellicle there occurs a extending which is exoskeletal in nature. This cover­ings are made up of not natural materials in numerous flagellates and Sarcodina. In testate Sarcodina the covering is consisted of of sili­ceous plates. The theca that Dinoflagellates is a close fitting one if the test and also the lorica are loose fitting ones.

3. Main capsule:

The central capsule of the Radiolarians consists of the cell core or the nuclei and is a specialty chamber where reproductive procedures go on. This capsule is taken into consideration as a security organelle.

4. Endoskeletal plates:

In plenty of ciliates belonging to the family of Ophryoscolecidae which reside as commensals in the stomach that ruminants, the existence of a conspicuous endoskeletal plate is encountered. These plates arise indigenous the oral region and run to the posterior an ar and are made up of hemicellulose or prismatic blocks of paraglycogen.

5. Axostyle and also parabasal apparatus:

It is a flexible rod-like structure running with the totality length the the body. Numerous Polymastigina and also Hypermastigina be affected by each other axostyle. It is thought to carry out a support­ive function. Parabasal device is a little or a long body coiled roughly the axostyle and also its function is unknown.

6. Costa and Cresta:

In Trichomonad flagellates a vulnerable filamentous structure prolonging from the blepharoplast to the basic of the undulating membrane is seen. That acts together a assistance to the undulating membrane. Cresta is a triangular membrane the extends posteriorly native its anchorage close to the nu­cleus and also is that unknown function.

7. Oral basket:

In many Gymnostomalous ciliates the cytopharyngeal wall surface is inside wall by a variety of rod-like structures. These rods type a type of basket and are considered as security structures.