Protista (Protistos = Primary) includes unicellular eukaryotes and show the following characters :
(1) Protists include solitary unicellular or colonial unicellular eukaryotic organisms which not form tissues.
(2) The unicells may be naked or covered by cell wall, pellicle, cuticle or shell.
(3) Simple multinucleate organisms or stages of life cycles occur in a number of groups.
(4) The organisms possess double and porous nuclear membranes, mitochondria, golgibody, plastids (in many), vacuoles, lysosomes and ribosomes is also present. Centrosome is occur in many cases.
(5) In many forms, plastids, (9+2 strand) flagella and other organelles are present.
(6) Some protists possess contractile vacuole for regulation of their water content.
(7) Their reproductive cycles typically include both asexual divisions of haploid forms and true sexual processes with karyogamy and meiosis.
(8) The organisms move by flagella or by other means or are non-motile.
(9) It may be photosynthetic, holotrophic, saprotrophic, parasitic and symbionts. Some have mixotrophic nutrition (holotrophic + saprobic). The photosynthetic, floating protists are collectively called phytoplankton. The free-floating, holozoic protozoans are collectively termed zooplankton.
(10) Asexual reproduction is the most common method in protists. It involve binary fission (Paramecium, Euglena, Amoeba), multiple fission (Amoeba), plastotomy (Opalina), budding (Paracineta, Arcella) and spore formation (Slime moulds).
(11) Sexual reproduction is believed to have originated in primitive protists. It involve isogamy (Monocystis), anisogamy (e.g., Ceratium) and oogamy (e.g., Plasmodium).
(12) Unicellular protists have been broadly divided in to three major groups :
(1) This is well defined group of unicellular, golden-brown photosynthetic organisms. Majority of them are motile and flagellated but a few are non-motile and non-flagellated. Flagellated forms exhibit peculiar spinning movement. Hence, they are called whorling whips.
(2) The cell wall of dinoflagellates, if present, is composed of a number of plates made up of cellulose. It is called theca or lorica. The theca contains two grooves-longitudinal sulcus and transverse girdle or annulus.
(3) Usually the cells possess two flagella which are of different types (heterokont).
(4) Trichocysts are rod like or spindle shaped ejective structures which occur just below the cell membrane.
(5) Cells possess a relatively large and prominent nucleus known as mesokaryon. DNA is without association with histone.
(6) There are numerous discoid chloroplasts without pyrenoids. They are yellow-brown to dark-brown in colour due to presence of characteristic pigments – Chlorophyll a, c, – carotene and xanthophylls (including dinoxanthin and peridinin).
(7) The reserve food material is starch in fresh water forms and oil in marine forms.
(8) The cells possess an osmoregulatory organelle called pusule which superficially looks like contractile vacuole.
The cells posses mitochondria, ribosomes and golgi bodies. They also possess mucilage bodies or vesicles below the cell membrane.
(9) In dinoflagellates it is mainly holophytic or photosynthetic. However, some forms are saprobic, parasitic, symbiotic or holozoic. For example, an colourless Blastodinium is parasite on animals.
(10) Dinoflagellates reproduce asexually through cell division or by the formation of zoospores and cysts. The cell division starts from posterior end. During cell division, centromeres and spindle are not seen. The spindle is replaced by cytoplasmic microtubules. During mitosis, the chromosomes break up into pairs of chromatids. The nuclear envelops and nucleolus persists during division.
(11) If sexual reproduction occurs, is isogamous or anisogamous. Two cells conjugate by a conjugation canal where the two amoeboid gametes fuse to form a diploid zygote. Life cycle involves zygotic meiosis (e.g.,Ceratium, Gymnodinium etc.) or gametic meiosis (e.g.,Noctiluca).
(1) Most of the diatoms occur as phytoplanktons both in fresh and marine waters. A few forms occur as benthos the bottom of water reservoirs. Diatoms constitute a major part of phytoplankton of the oceans.
(2) The cells of diatoms are called frustules or shell. They are microscopic, unicellular, photosynthetic organisms of various colours and diverse forms. They may be circular, rectangular, triangular, elongated, spindle-shaped, half-moon shaped, boat-shaped or filamentous. Incipient filament occur in Melosira.
(3) They exhibit mainly two types of symmetry-radial symmetry as in centrales (e.g.,Cyclotella, Biddulphia, Triceratium, Melosira) and isobilateral symmetry as in Pennales (e.g.,Pinnularia, Synedra, Actinella, Navicula).
(4) The cells of diatoms are called frustules. The cell wall is chiefly composed of cellulose impregnated with glass-like silica. It shows sculpturings and ornamentations. It is composed of two overlapping halves (or theca) that fit together like two parts of a soap box. The upper half (lid) is called epitheca and the lower half (case) is called hypotheca.
(5) Diatoms do not possess flagella except in the reproductive stage. They show gliding type of movement with the help of mucilage secretion. They float freely on the water surface due to presence of light weight lipids.
(6) Raphe is a cleft in the valve which occur in diatoms performing gliding movement. Raphe is often longitudinal, sigmoid with central and polar nodules.
(7) Each cell has a large central vacuole in which a prominent nucleus is suspended by means of cytoplasmic strands. The cells are diploid (2N). In case of centrales, the nucleus lies in the peripheral region.
(8) The cells possess plate-like or discoid chromatophores (or chloroplasts). They contain chlorophyll a, and c, carotenes, diatoxanthin, diadinoxanthin and fucoxanthin (chl. b is absent).
(9) Some species of diatoms are devoid of chromatophores, e.g.,Nitzschiaalba. The are saprotrophic in nutrition.
(10) The reserve food material is oil and a polysaccharide – chrysolaminarin (or leucosin).
(11) Asexual reproduction is most common method of multiplication is binary fission (cell division) that occurs at night.
(12) Sexual reproduction takes place by the fusion of gametes. Meiosis is gametic i.e., takes place during the formation of gametes.
(1) It includes Euglena like flagellate protists of fresh water and damp soils which were formerly placed in phytomastigophora by zoologists. Euglenoids include about 36 genera and 800 species.
(2) Euglenoids and their non-motile relatives are unicellular flagellate protists.
(3) These protists are devoid of cellulose cell wall. The body is covered by thin and flexible pellicle. The pellicle has oblique but parallel stripes called myonemes. The pellicle is composed of fibrous elastic protein and small amount of lipid or carbohydrates.
(4) The euglenoids have two flagella, usually one long and one short. Each flagellum arises from a basal granule (blepharoplast). The flagella bear hair.
(5) They can undergo creeping through expansion and contraction of body called metaboly.
(6) The apical end bears an invagination having three parts–cytostome (mouth), cytopharynx (gullet or canal) and reservoir. The cytostome is generally eccentric.
(7) The two flagella join with each other at a swelling called paraflagellar body. An orange red coloured eye-spot or stigma is located at the base of flagellum attached to the membrane of reservoir at the level of paraflagellar body. They contain red pigment astaxanthin. Both paraflagellar body and eye spot act as photoreceptors and direct the organism towards the optimum light.
(8) An osmoregulatory contractile vacuole occurs in the anterior part of the cell below the reservoir.
(9) A single large nucleus lies roughly in the middle. The nuclear envelope persists during division. The nucleolus also persists upto metaphase.
(10) Nutrition is holophytic (photoautotrophic), saprobic (e.g.,Rhabdomonas) or holozoic (e.g.,Peranema). Even holophytic forms can pick up organic compounds from the outside medium. Such a mode of nutrition is called mixotrophic.
(11) Product of photosynthesis is paramylon which is stored in the form of paramylum granules in the paramylum bodies in cytoplasm.
(12) Sexual reproduction has not yet been definitely proved. Under favourable conditions, euglenoids multiply by longitudinal binary fission.
(13) These protists perennate during unfavourable periods as cysts.
Example : Euglena, Phacus, Eutreptia, Trachelomonas, Peranema.
Euglena
General characters
(1) Euglena is a connecting link between animals and plants.
(2) Euglena resembles the ancestral form which the plants and animals evolved.
(3) Euglena is a free swimming fresh water flagellate.
(4) Body is covered by pellicle, a small cytostome (cell mouth) and cytopharynx is present at the anterior end of the body.
(5) Euglena contains chlorophyll, yet it resembles animals, because it feeds like animals in the absence of sunlight.
(6) Nutrition in Euglena is mixotrophic, when light is available it is photosynthetic, in darkness it is saprophytic absorbing food from surrounding water.
(7) Reserve food is stored in the form of paramylum or paramylon.
(8) Movements are called euglenoid movements (wriggling movements), also moves with help of flagella.
(9) Asexual reproduction occurs by longitudinal binary fission, no sexual reproduction.
Consumer / Decomposer protists
Slime moulds include very interesting and peculiar organisms which share the characters of both animals and fungi. Due to this peculiarity they are commonly called fungus animals. Modern biologist include slime moulds under the kingdom-protista and called them protistan fungi.
General characters
(1) They do not have chlorophyll.
(2) They are surrounded by the plasma membrane only (somatic parts are without cell walls).
(3) At one stage of the life cycle they have amoeboid structure.
(4) The slime moulds live usually amongst decaying vegetation. They are quite common on lawns and moist fields.
(5) They exhibit wide range of colouration.
(6) They have phagotrophic or saprotrophic nutrition. Parasitic forms are not known
(7) The sporangia produce spores. Each spores possesses a cellulose cell wall.
(8) The slime moulds resemble both protozoa and the true fungi. They are like protozoa in their amoeboid plasmodial stage and similar to true fungi in spore formation. Slime moulds are of two types :
Acellular (Plasmodial) Slime moulds
General characters
(1) Acellular slime moulds commonly grow as slimy masses on damp places rich in dead and decaying organic matter.
(2) The somatic phase is diploid and consists of a free living organic matter multinucleated protoplasm called plasmodium.
(3) The plasmodium slowly streams or glides over decaying organic matter putting out blunt finger like pseudopodia showing amoeboid movement.
(4) They also absorb dissolved organic substances from the substratum showing saprotrophic nutrition.
(5) Under unfavourable conditions the plasmodium contracts and gets surrounded by thick horny wall. It is called sclerotium.
(6) Each plasmodium reproduces asexually by the formation of several, small, sessile or stalked, brightly coloured sporangia.
(7) The multinucleated protoplasm of sporangium is cleaved to produce a large number of small uninucleate spores.
(8) When fully mature, the wall of the sporangium bursts to release the spores. The spores are dispersed by air.
(9) On germination, a spore generally releases one biflagellate, spindle-shaped swarm cell or a non-flagellate myxamoeba. The myxamoebae feed on bacteria and yeasts and multiply in number. The swarm cells swim about actively and finally fuse in pairs at the posterior nonflagellate ends to form zygotes.
(10) The diploid nucleus of zygote undergoes repeated mitotic divisions. As a result, the zygote gradually changes into a multinucleate amoeboid structure, the plasmodium. The plasmodium repeats the life cycle.
(1) The cellular slime moulds occurs in the form of haploid uninucleated, naked (without cell wall) cell covered by plasma membrane. These cells are called myxamoebae.
(2) The myxamoebae move freely with the help of amoeboid movement and phagotrophic or holozoic nutrition.
(3) They grow and divide to form a large population of individuals.
(4) Under unfavourable condition a myxamoeba secrete a rigid cellulose wall to form the microcyst. Microcyst formation is a means of perennation.
The microcysts can be dispersed. On the return of favourable conditions, the microcyst wall ruptures to release a myxamoeba. The latter resumes its function of feeding, growth and multiplication forming amoeboid cells.
(5) When the food supply is exhausted, the amoeboid cells get aggregated without any fusion. The stimulus for the aggergation process is due to release of cyclic adenosine monophosphate (cyclic AMP) from the amoeboid cells. This aggregated mass of cells is called pseudoplasmodium. It is a sort of community association. Because of this reason, cellular slime moulds are called the communal slime moulds.
(6) The pseudoplasmodium crawls about until it settles at one point and from a stalked, branched or unbranched fruiting structure called sporocarp. The multicellular stalk of sporocarp is formed from the front part of the pseudopodium while the rear end forms the naked sporangium.
(7) The stalk of sporocarp may remain upright or bend. Finally the spores are released and disseminated.
(8) Some time the myxamoebae form clusters. The central myxamoeba of the cluster engulfs a surrounding myxamoeba to become larger structure which forms a thick wall to form the zygote. This zygote is called macrocyst. Karyogamy occurs inside the macrocyst which is followed by meiotic and several mitotic divisions. Ultimately the macrocyst wall ruptures to release a number of haploid myxamoebae.
(9) The most important character of cellular slime moulds is the complete absence of flagellated cells in their life cycle.
(10) The cellular slime moulds resemble plant in having cellulose cell wall in spores and resemble animals in having amoeba-like myxamoebae.
Examples : Dictyostelium, Polysphondylium.
Protozoan protists (Gr. Protos = first ; zoon = animal)
It include all unicellular (or acellular) eukaryotic animals. These are most primitive organisms considered as animals because of heterotrophic nutrition and motility. About 50,000 species (30,000 present and 20,000 extinct) are so far known.
Brief history : Protozoans were first studied by Leeuwenhoek (1677). The name “Protozoa” was coined by Goldfuss (1817). The branch of their study is called Protozoology.
General characters
(1) Protozoans are the simple and primitive organisms.
(2) They are free living or parasitic.
(3) All the free living forms are aquatic.
(4) They are asymmetrical or radially symmetrical or bilaterally symmetrical.
(5) They are unicellular (acellular).
(6) They have protoplasmic grade of organization.
(7) Locomotion is effected by flagella, cilia or pseudopodia.
(8) Nutrition is holophytic, holozoic, saprozoic or parasitic.
(9) Digestion is intracellular.
(10) Excretion and respiration occurs by diffusion.
(11) In fresh water protozoans osmoregulation is carried out by the contractile vacuoles.
(12) Encystment is a common phenomenon.
(13) Reproduction occurs by asexual and sexual methods.
Classification of Protozoans
Protozoans are classified on the basis of locomotory organelles into following classes.
Class 1. Rhizopoda or Sarcodina
(1) There is no definite cell wall or pellicle.
(2) There is no definite shape.
(3) The locomotory organs are pseudopodia.
(4) There is no permanent mouth or anus.
(5) The contractile vacuoles are present in the fresh water forms.
The rhizopoda has been divided into five orders. They are as Lobosa, Filosa, Foraminifera, Heliozoa and Radiolaria.
q Actinophryx is called ‘Sun animalcule’ as it resemble the sun.
Class 2. Flagellata or Mastigophora
(1) The body is covered by a thin pellicle or cuticle.
(2) The locomotory organs are flagella.
(3) The contractile vacuoles are present in fresh water forms with accessory vacuoles.
(4) Chloroplast are found in some forms.
(5) They may be free living or parasitic.
The class flagellata has been divided into eight orders. They are as Chrysomonadina, Cryptomonadina, Euglenoidea, Phytomonadina, Dinoflagellata, Cystoflagellata, Protomonadina and Polymastigina.
q Trychonymph (symbiotic) live in alimentary canal of termite that is digest to cellulose.
q Noctiluca shows bioluminiscense due to luciferin protein. It is also called the ‘Fire of sea’.
Class 3. Sporozoa
(1) They are exclusively endoparasitic.
(2) The body is covered by pellicle.
(3) Reproduction takes place by spore formation.
The class is divided into two sub-classes, namely, Telosporidia and Neosporidia.
Sub-class (i) Telosporidia
(1) The spores do not contain polar capsules or filaments.
(2) The life history ends with the formation of spores.
(3) The spore cases are simple and contain many spores.
Examples : Monocystis, Gregarina, Isopora, Eimeria, Plasmodium, Babesia etc.
q Babesia causes the ‘Taxas cattle fever’ in animals. This disease also called ‘Red water fever’ or Haemoglobin uric fever.
q Monocystis is found in seminal vesicle of earthworm, and causes sterlity in earthworm. It is monogenetic in nature.
q Eimeria is found in epithelial cells of liver of Rabbit.
Sub class (ii) Neosporidia
(1) The trophozoite is amoeboid multinucleated.
(2) Spore cases are complex usually having a single germ.
Examples : Nosema, Myxidium, Globidium etc.
Class 4. Ciliophora
(1) The body is covered by thin pellicle.
(2) They have a fixed permanent shape.
(3) The locomotory organs are cilia.
(4) Tentacles are present.
The class ciliophora is divided into two sub-classes, namely Ciliata and Suctoria.
Sub-class (i) Ciliata
(1) Cilia are present throughout life.
(2) Tentacles are absent.
(3) Mouth and cytopharynx are usually present. Cytopyge is a temporary anal apperture.
(4) Contractile vacuoles are present.
(5) Trichocysts, organs of offense and defence are present in certain forms.
Examples : Paramecium, Stylonchia Vorticella etc.
q Vorticella is called ‘Bell animalcule’. It is a pedicellate protozoan.
q Nyctotherus is a parasite in the rectum of frog. It is also found in the rectum of cockroach.
Sub-class (ii) Suctoria
(1) Cilia are present only in the young conditions and adults are devoid of them.
(2) Tentacles are present in the adult.
(3) One to many contractile vaculoes are present.
Examples : Acineta, Dendrocometes, Dendrosoma etc.
Some representative protozoan protists
General characters
(1) Amoeba belongs to the class Sarcodina or Rhizopoda of the phylum protozoa. It is discovered by Russel Von Rosenhoff in 1755.
(2) The most common species of Amoeba proteus. Proteus is the name of the mythical sea god who could change shape.
(3) Amoeba is cultured in laboratory by Hay infusion method.
(4) Body is covered by plasmalemma. It is a trilaminar and selectively permeable membrane. Plasmalemma is excretory, ammonia diffuses out through it. It is also respiratory diffusion of oxygen and carbon dioxide takes place through it.
(5) The body bears a member of temporary and blunt pseudopodia. The type of pseudopoium found in Amoeba proteus is lobopodium. Pseudopodia are composed of both ectoplasm and endoplasm.
(6) Pseudopodium at its forward end gets its from consistency by hyaline cap which is made of ectoplasm.
(7) Pseudopodia in Amoeba are meant for feeding and locomotion.
(8) Pseudopodia are found in Amoeba and leucocyte of higher animals.
(9) Cytoplasm is differentiated into outer ectoplasm and inner endoplasm. Endoplasm is divided into outer plasma gel and inner plasma sol.
(10) Locomotion of Amoeba is known as amoeboid movement. Sol gel theory of amoeboid movement was first given by Hyman supported by Pantin and Mast. According to this theory amoeboid locomotion is due to change in the velocity of cytoplasm.
Table : 2.3-1 Theories of Amoeboid Movement
Surface tension theory
Berthold
(1886)
Rolling movement theory
Jennings
(1904)
Walking movement theory
Dellinger
(1906)
Sol-gel theory
Hyman
(1917)
Folding and unfolding theory
Goldacre and Lorch
(1950)
Contraction-hydraulic theory
Rinaldi and Jahn
(1963)
(11) Sol gel conditions are due to contraction and relaxation of long chains of proteins.
(12) Amoeba contains a nucleus, a contractile vacuole, a number of food vacuoles and other cell organelles.
(13) Endoplasm of Amoeba in the posterior part contains a single clear rounded and pulsating contractile vacuole. Contractile vacuole is concerned with osmoregulation, i.e., removal of excess of water.
(14) Vacuole is found only in fresh water forms. It is absent in marine and parasitic forms.
(15) If an Amoeba is placed in distilled water its contractile vacuole works faster while it is placed in salt water, its contractile vacuole will disappear.
(16) Contractile vacuole of Amoeba is analogous (similar in function) to uriniferous tubules of frog.
(17) Food of Amoeba consists of bacteria, diatoms, small protozoa and algae.
(18) The process of ingesting solid food is phagocytosis, Amoeba ingest food by import, circumfluence, circumvallation or invagination.
(19) Import involves passive sinking of food into body by rupture of plasmalemma, e.g., Ingestion of algae.
(20) Circumfluence is the ingestion of less active or motionless organisms like bacteria.
(21) Circumvallation is the engulfment of active prey like ciliate or flagellate.
(22) Digestion in Amoeba is intracellular. Amoeba secretes digestive enzymes for hydrolysing starch, protein, fat etc.
(23) Food vacuole of Amoeba is analogous to the alimentary canal of an animal or gastro vascular cavity of Hydra. The contents of food vacuole in Amoeba first becomes acidic then alkaline.
(24) Egestion of undigested food in Amoeba takes place through a temporary rupture of the surface membrane.
(25) Amoeba responds to environmental conditions. Response to the stimuli is called taxis. Different taxis are thermotaxis (temperature) phototaxis (light), thigmotaxis (touch), chemotaxis (chemicals), galvanotaxis (electric current), geotaxis (gravity) and rheotaxis (water current).
(26) Normal method of asexual reproduction is binary fission. Binary fission is a process of mitosis. It takes place when food is abundant and temperature is suitable.
(27) Multiple fission or sporulation takes place during unfavorable conditions after encystment. There are three layers of cysts.
(28) Lack of oxygen and food induces encystment product of multiple fission are called ‘Amoebulae’.
(29) Amoeba regenerates from nucleated bits.
Pseudopodia : These are found in those forms which do not possess a definite pellicle. According to size, structure, and shape pseudopodia may be of different types as :
Lobopods : These are short, blunt and thick finger like out growth of ectoplasm with an axial core of endoplasm e.g.,Amoeba, Arcella etc.
Filopods : They are cylindrical thread like, formed entirely of ectoplasm and radiate from the body in all directions e.g.,Euglypha, Radiolaria.
Reticulopods : They are filamentous which form a network of pods e.g.,Polystomella, Chlamydophrys.
Axopods : These are long stiff semi-transparent extensions of cytoplasm with pointed distal ends e.g., Actinophrys.
General characters
(1) Entamoeba histolytica is a parasitic and pathogenic protozoan protists which resides in the upper part of large intestine in human beings. It causes amoebic dysentery or amoebiasis.
(2) Lamble (1859) discovered E. histolytica. Friedrick Losch, a Russian Zoologist, discovered its pathogenic nature in 1875.
(3) It has two forms, adult trophozoite or magna, pathogenic form found in the mucosa and sub-mucosa of intestine forming ulcers and minuta, nonpathogenic form found in the lumen of intestine.
(4) Entamoeba has no contractile vacuole.
(5) Trophozoite of Entamoeba reproduces by binary fission. Minuta form encysts. A mature cyst is called quadrinucleate cyst. It has four nuclei and two chromatoid bodies.
(6) Quadrinucleate cyst is the infective stage. Infection is oral through contaminated food and water.
(7) The reserve food material in cyst of E. histolytica is glycogen. A single cyst of E. histolytica produces eight amoebulae.
(8) It damages instestinal mucosa by secreting an enzyme-histolysin.
Entamoeba gingivalis is a parasite of human teeth, found in the abscesses of gum and in pus pockets of pyorrhoea, bleeding gums. It increase pyorrhoea disease but does not cause it. Pyorrhoea is caused by Trichomonastinax. Adult is called trophozoite and has 2-3 pseudopodia. It feeds on WBCs, bacteria and pus cells. Cyst is not formed in E. histolytica and infection occurs by direct contract like kissing.
General characters
(1) Trypanosoma gambiense is the parasite zooflagellate which causes one of the deadliest ailments in human beings called African sleeping sickness or Trypanosomiasis. It was discovered by Frode in 1901.
(2) Trypanosoma is usually found in the blood of vertebrates, finally invading cerebrospinal fluid.
(3) Trypanosoma is an endoparasite, blood parasite, extra cellular parasite.
(4) Trypanosoma has a nucleus, a flagellum, undulating membrane, blepharoplast (basal granule) and kinetoplast. The flagellum arises from the posterior end and runs anteriorly with undulating membrane.
(5) Trypanosoma reproduces asexually by longitudinal binary fission. It does not form cysts.
(6) Trypanosoma is polymorphic and has four forms: Leishmania, Leptomonad, Crithidial and Trypanosomal (= Metacyclic) stages.
(7) Trypanosoma is digenetic, it completes its life cycle in two hosts. The primary or principal or definite host is man and the intermediate or secondary host or vector is the insect, tse-tse fly or bug.
(8) Three important species of Trypanosoma for which man is host are : Trypanosoma gambiense, T. rhodesiensi and T. cruzi.
(9) The chief vector host of T. gambiense transmitting the disease from one man to another is the tse-tse fly, Glossina palpalis. Occasionally, Glossina tachinoides also act as a vector.
(10) T. rhodesiensi causes Rhodesian trypanosomiasis, it is confined to east central parts of Africa, particularly Rhodesia. The insect vectors for T. rhodesiense are tse-tse flies mainly Glossina morsitans and G. pallidipes.
(11) T. cruzi is the causative agent of South American trypanosomiasis or Chaga’s disease T. cruzi is transmitted by bugs like Triatoma and Panstrongylus. Symptoms of Chaga’s disease are fever, diarrhoea, anaemia and enlargement of lymphoid glands etc.
They are spore forming parasitic protists which lack locomotory structure and contractile vacuoles. The body is covered by pellicle or cuticle.
Systematic position
Phylum – Protozoa
Sub-phylum – Plasmodroma
Class – Sporozoa
Sub-class – Telosporidia
Order – Haemosporidia
Genus – Plasmodium
species – vivax
History : The term malaria was coined by Mucculoch in 1827.
Lancisi first suspected a relationship between malaria and mosquito.
Laveran (1880) discovered that malaria is caused by a protozoan parasite, Plasmodium vivax.
Sir Ronald Ross was (1896) the first to observe oocytes of Plasmodium in female Anopheles.
Gassi (1896) was the first to describe the life cycle of Plasmodium in Anopheles.
Host : It is digenetic i.e., life cycle completed on two hosts –
(1) Man (medically primary but biologically secondary host)
(2) Female Anopheles (medically secondary but biologically primary host).
Life cycle : During life cycle two important phases are present.
(1) Endogenous or Asexual phase : passes in man.
(2) Exogenous or Sexual phase : passes in female Anopheles mosquito.
In Man (Schizogony)
Infective stage : It is spindle shaped sporozoite introduced by female Anopheles along with saliva (for anticoagulant anophilin) during blood sucking. Sporozoite enters liver cells. In liver they produce several stages.
Pre-erythrocytic stage : Each sporozoite enters inside the liver cell and becomes spherical and termed as cryptozoite. It undergoes a pre-erythrocytic cycle completed in 10 days and multiplies asexually by schizogony. After rupturing schizont numerous cryptomerozoites are liberated.
Exo-erythrocytic stage : Cryptomerozoites enter in new liver cells and reproduce asexually to give rise to a large number of meta-cryptomerozoities, few are smaller in size and called micro-metacryptomerozoites.
Erythrocytic stage : Micro metacryptomerozoites enter into the blood stream and each enters the RBCs and assumes rounded disc like shape with single nucleus. It develops a vacuole which gives a ring like appearance. This stage is known as signet ring stage. During further development the vacuole is lost and parasite feeds on the cytoplasm of R.B.C. This stage is known as amoeboid stage or trophozoite stage. The matured trophozoite develops to become a schizont. It multiplies asexually by erythrocytic schizogony.
The schizont withdraws its pseudopodia and changes into rounded form. The nucleus divides into large number of nuclei which are arranged on the periphery and collect a little amount of cytoplasm around each. In this way merozoites are produced. This stage is known as Rosette stage. Merozoites are liberated into the plasma. New merozoites again enter fresh RBCs and repeat the erythrocytic cycle to produce large number of merozoites. Haemozoin liberated in blood plasma.
q Paroxysm : Actual attack of malaria occurs after a few initial erythrocytic cycles due to accumulation of haemozoin and toxins in blood. It involves rigour, febrile and defervescent stages.
Formation of gametes : Some merozoites do not enter schizogony but instead form gametocytes in RBCs. Gametocytes are of two types :
(1) Macro-gametocytes: These are female cells which are large in size, laden with food material and having nucleus at one end.
(2) Micro-gametocytes : These are male cells, small in structure and nucleus placed centrally.
In Mosquito (Sporogony)
When female Anopheles bites a patient of malaria, the parasites enter the alimentary canal of the insect. In the stomach of mosquito the asexual forms are digested and only gametocytes survive. Gametocytes are released in blood plasma in large numbers during mid night. They die by morning. Megagametocyte produces only one megagamete. Microgametocyte produces 4-8 motile microgametes by exflagelation.
Fertilization : Both mega and microgamete fuse, form zygote which narrows to becomes ookinete. Ookinete pierces the stomach wall and forms a cyst on its outer surface.
Sporogony : Oocyst undergoes a process of sporogony. The irregular cells thus formed are known as sporoblasts. The nucleus of sporoblast divides several times to give rise to daughter nuclei which migrate in the projections of sporoblast.
These minute projections change into the form of sporozoites. After maturity oocyst burst out and numerous sporozoites are liberated into the body cavity of mosquito. The sporozoites move towards salivary glands and bore into them. In this way they are ready for transmission.
Control of malaria
(1) Prevention from infection is called prophylaxis.
(2) Quinine is obtained from bark of Cinchona (discovered in Peru) which is most commonly used against malaria.
(3) Peludrine, atabrine, camoquinine, Chloroquinine are few other drugs effective against malaria.
(4) M. E. P. is Malaria Eradication Programme.
(5) G.B.P. is General Blood Picutre i.e., blood film made for the test of malaria.
Table : 2.3
Name
P. vivax
P. malariae
P.ovale
P. falciparum
1. Site
Liver and RBC of man
Liver and RBC of man
Liver and RBC of man
Liver and RBC of man
2. Distribution
Tropical countries subtropical
Tropical countries subtropical
West Africa and South America
Tropical countries
3. Duration of exoerythrocytic cycle or prepatent period
(1) Paramecium is a holotrichous ciliate protozoan. It is discovered by Hill in 1752.
(2) Paramecium is free-living and aquatic form. In laboratory, Paramecium is cultured by ‘Hay-infusion method’.
(3) Paramecium is commonly called as ‘Slipper animalcule’. Body is distinguished into an oral or ventral surface and an aboral or dorsal surface.
(4) Body is covered with a thin, firm, flexible membrane called pellicle. Entire body surface is covered by numerous cilia, the locomotory organelles. Cilia in the posterior end are longer called caudal tuft. Each cilium arises from a basal granule or kinetosome. Paramecium has infraciliary and neuromotor system to co-ordinate ciliary beat.
(5) Trichocysts are peculiar bottle-shaped organelles present in the ectoplasm of Paramecium. Trichocysts are the organelles of offence and defence.
(6) Paramecium is heterokaryotic (dimorphic nuclei) i.e., macronucleus and micronucleus. Macronucleus is one, large, kidney shaped, controls vegetative functions (metabolism). Micronuclei, one (P. caudatum), two (P aurelia) and several (P. multimicronucleatum) are only concerned with reproduction.
(7) Oral apparatus consists of cytopharynx and cytostome (mouth), cytopyge or cytoproct (anus). Nutrition or food intake in paramecium is holozoic. Paramecium is a filter feeder and feeds on small protozoa, unicellular plants (algae), diatoms, yeast etc. and small bits of animals and vegetables. Most favourite food is Tetrahymena, another ciliate protozoa.
(8) Digestion in paramecium is intracellular. Food vacuole constantly moves along a definite courses (cyclosis) within streaming endoplasm. Food vacuole is digested in the cell body in acidic to alkaline media. Egestion of undigested food takes place through cytopyge or cytoproct, a temporary formed anus.
(9) Paramecium reproduces by transverse binary fission and nuclear reorganisation. Binary fission occurs during favourable condition. In this process, macronucleus divides amitotically and micronucleus mitotically.
(10) Paramecium undergoes several kinds of nuclear reorganisation such as conjugation, autogamy, cytogamy, endomixis and hemimixis. Nuclear reoganisation takes place for rejuvenation.
(11) Conjugation occurs between two mating types of same species of Paramecium. It is a modified form of cross fertilization. Each conjugant produces a female stationary and a male migratory nucleus by three successive divisions of micronucleus. They are called pronuclei.
(12) Synkaryon is the diploid nucleus formed by the fusion of stationary and migratory nuclei in conjugant. Synkaryon divides thrice to form eight nuclei. At the end of the conjugation each Paramecium (exconjugant) produces four daughter Paramecia.
(13) Autogamy is a process of self fertilization. It occurs in a single animal of P. aurelia. Autogamy results in the production of two daughter paramecia from each.
(14) Cytogamy occurs in P.caudatum. The two cytogamonts do not exchange their male pronuclei. Endomixis occurs in P.aurelia. It is an asexual reproduction. Hemimixis is the process of purification act on the part of meganucleus.
(15) Paramecium has kappa, Lambda, Mu and Pi particles in cytoplasm. They differentiate paramecia between sensitive and killer forms.
? Dinoflagellates with bioluminescence/phosphorescence due to light producing protein luciferin are called fire algae. e.g.,Noctiluca, Pyrocystis, Pyrodinium etc. Noctiluca is also called ‘night light’.
? Dinoflagellates symbionts in other protists and invertebrates are called zooxanthellae.
? Some dinoflagellates produce red tides of oceans. e.g.,Gonyaulax, Gymnodinium etc.
? Photosynthetic protists fix about 80% of CO2 in the biosphere.
? The siliceous frustules of diatoms do not decay easily. They pile up at the bottom of water reservoirs and form big heaps called diatomite or diatomaceous earth. Diatomite is porous and chemically inert.
? 29th August is celebrated as the ‘mosquito day’ because Sir Ronald Ross established mosquito malaria relationship on August 29, 1897. He got Nobel prize in 1902.
? 20th August is malaria day. Ministry of health, government of India started National Malaria Eradication Programme (NMEP) in the year 1953.
? Some protozoans have a loose exoskeleton called “Lorica hourse” on them.
? The fastest reproducing protozoan is ‘Glaucoma’. It produces 6-generation within 24 hrs.
? Oblique binary fission in Ceratium.
? Polystomella is dimorphic rhizopod which shows metagenesis or alternation of generation in its life cycle.
? Leismania is in intracellular parasite of man and other mammals. It causes Leishmaniasis. L.donovani causes Kala-azar in man.
? Proterospongia is a fresh water colonial and free living flagellate and is connecting like between protozoa and porifera.
? Certain protozoan like Colonympha and Trichonymphya help in digestion of cellulose in certain insects.
? Flagellates are more simplest protozoan while ciliates are most complex protozoans.
? E. coli found as an endocommensal in the colon of about 50% population. It is non-pathogenic.
Photosynthetic and consumer protists
In the five kingdom classification which kingdom occupies intermediate position from phylogenetic point of view
(a) Monera (b)Protista
(c) Plantae (d) None of the above
Which kingdom incorporates phytoplanktons and zooplanktons
(a) Protista (b) Fungi
(c) Animalia (d) Plantae
Which organism behaves like plants in the presence of light and absence of organic food, but in reverse conditions behaves like animals
(a) Archaebacteria (b) Euglena
(c) Nostoc (d) Paramecium
In Whittaker’s five kingdom classification, unicellular eukaryotes primarily aquatic and having various cell organelles constitute [Chd. CET 1997]
(a) Monera (b) Protista
(c) Animalia (d) Plantae
Planktons are organisms which [JIPMER 1993]
(a) Float on water surface (b) Are free swimmers
(c) Are deep sea forms (d) Are burrowing forms
If phytoplanktons are destroyed in the sea, then
[BHU 1991]
(a) No effect will be seen
(b) Primary consumers will grow luxuriently
(c) It will effect the food chain
(d) Algae will get more space to grow
Phytoplankton consists of [AMU 1991]
(a) Non-vascular hydrophytes
(b) Aquatic algae and photosynthetic bacteria
(c) Micro-organisms functioning as decomposers
(d) Plant consuming animals and their remains
Flagellar movements are controlled by
(a) Photosynthesis (b) Contractile vacuoles
(c) Neuromotor apparatus (d) Pyrenoids
Euglena belongs to kingdom
(a) Monera (b) Protista
(c) Plantae (d) Animalia
The scientist who coined the term ‘protista‘ to include both plant and animal like unicellular organism was [BHU 1982]
(a) Aseptate and multinucleate (b) Septate and multinucleate (c) Aseptate and uninucleate (d) Septate and uninucleate Answer. (b) The mycelium of Aspergillus consist of branch septate hyphae. Cells of hyphae are multinucleate. (185)
(a) Parenchyma (b) Chlorenchyma (c) Plectenchyma (d) Collenchyma Answer. (c) Plectenchyma (Pseudoparenchyma) is nothing but the interwoven mass of fungal mycelium which in cross-section look like parenchyma. (108)
(a) Colletotrichum falcatum (b) Phytophthora infestans (c) Potato mosiac virus (d) Alternaria solani Answer. (b) Late blight of potato is a seed born disease which is caused by Phytophthora infestans. The disease is characterised by brownish to blackish dead areas …
