Euglena viridis Introduction Large no. of small protozoans Moving with flagella Superclass Mastigophora Typical plant or animal-like Chlorophyll bearing plastids Autotrophic Photosynthesis Heterotrophic Either phyto or zoomastigophorea Typical phytoflagellate Autotroph in sunlight Heterotroph in dark Suitable for class study Green Eye-like photoreceptive structure Gr., eu=true+ glene=eyeball + L., viridis= green Systematic Position Phylum- Protozoa Subphylum- Sarcomastigophora Superclass- Mastigophora Class- Phytomastigophora Order- Euglenida Genus- Euglena Species- viridis Ecology Solitary, free living, freshwater flagellate Occurs in freshwater ponds, pools, ditches, slow running streams with vegetation Fairly active Found at various depths below water surface Ponds in well maintained gardens, with decaying nitrogenous organic matter (feces of animals, leaves, twigs): good sources Sometimes so abundant that water appears green as a film of scum on water surface Structure 1. Shape & Size Small microscopic 60μ in length Body elongated, spindle shaped Anterior end round or blunt Middle part wider Posterior end pointed From anterior end arises a whip-like flagellum Moves as animal progresses 2. Pellicle Body covered by a distinct, thin, elastic & tough pellicle Lies beneath plasma membrane Flexible, permits movement Made of protein, no cellulose like plants  Electron microscopy: pellicle consists of thin, elastic & helically disposed strips Fused at both ends of cell body with a groove along the edge & a ridge along the other Ridges overlap & articulate with each other Light microscope: edges as striations (myonemes) Beneath pellicle is mucussecreting muciferous bodies & bundles of microtubules 3. Cytoplasm Enclosed by pellicle Divided into 2 zones: 1. Ectoplasm 2. Endoplam a. Ectoplasm Clear, dense, narrow peripheral zone ( microtubules & muciferous bodies) b. Endoplasm More fluidlike granular central zone (nucleus & other inclusions) 4. Reservoir  Invagination at anterior end, forms a permanent flask shaped cavity: reservoir to short tubular canal (cytopharynx) by cytostome Lined by plasma memb. 5. Flagellum Single thread-like arises from cytostome at anterior end Made up of an axial elastic filament (axoneme) covered by protoplasmic sheath Electron microscopy: flagellum is paired not single Smaller 1 confined to reservoir Both originate: 2 tiny blepharoplasts, base of cytostome Long flagellum has swelling (paraflagellar body) acting as photoreceptor (lactoflavin as sensitizer) 6. Nucleus Single, large, spherical, vesicular near centre of endoplasm Towards posterior end of body Contains large solid, central body (Karyosome) Function controversial Double nuclear membrane with pores Electron microscope: nucleoplasm with several nucleoli, large number of granular & thread-like chromosomes 7. Contractile Apparatus Associated with reservoir: dense osmoregulatory zone Includes a large central contractile vacuole Surrounded by several small accessory vacuoles fuse to form larger one Discharge of water along with some waste products of metabolism to outside via reservoir, cytopharynx & cytostome 8. Stigma A shallow cupshaped pigmented red spot (eye spot or stigma) near reservoir Leede (1966) composed of lipid droplets, with red pigment (carotenoid) Stigma & paraflagellar body: photoreceptor apparatus When Euglena moves toward light, receptor illuminated When, changes direction, shadow of pigment falls on receptor So animal depend on sunlight for photosynthesis orients itself towards light 9. Endoplasmic Inclusions Besides, contractile apparatus & stigma other inclusions are: a.Chromatophores b.Paramylon c.Other cytoplasmic structures a. Chromatophores Numerous green bodies giving green color as loaded with chlorophyll a, b & β-carotene Slender, radiate from central point to form star grouping Center with single proteinaceous pyrenoid (forms starch-like substance: paramylum) Chloroplast: groups of chlorophyll bearing lamellae (thylakoids) with 3 lamellae Placed in matrix or stroma, containing ribosomes & fat Each chloroplast bounded by a triple membrane envelope b. Paramylon Several small free oval granules (paramylon) in endoplasm Polysaccharide (β-1, 3-glucan) similar to starch not identical Not coloured blue with iodine Produced by photosynthesis ,reserve food material c. Other Cytoplasmic Structures Golgi bodies: piles of large flattened sacs with minute vesicles ER: as small interconnecting tubules & vesicles Mitochondria: tubular cristae & more in number near reservoir Ribosomes: scattered freely in endoplasm, ER & chloroplasts Locomotion 1. Flagellar Movement Swims freely in water by single, locomotory flagellum During swimming, flagellum directed obliquely backward Undergoes spiral undulations with waves passing from base to tip: sideways lashing Flagellum beats at 12 beats/second Beating drives water backward & induces whole body to move forward Each beat not only throws body forward but also to 1 side Beats repeated again, animal moves in circles With every beat animal also rotates on its axis Rotates at rate of 1 turn/second 2. Euglenoid Movement Flexible pellicle enables peristaltic activity Bringing worm-like wrigglings while animal creeps on bottom As peristaltic waves pass, body becomes shorter & wider first at anterior end, then middle & then posterior end Characteristic of Euglena Bending caused by secretion of underlying muciferous bodies Nutrition Autotrophic or holophytic, saprozoic Dual mode: Mixotrophic No evidence of animal-like of holozoic mode 1. Holophytic/Autotrophic Chief mode Like green plants can manufacture own food in sunlight by photosynthesis with chlorophyll present in chloroplasts Chlorophyll absorbs energy from sunlight With this energy water reacts with CO2 in a series forming hexose sugar Converted polysaccharide (paramylon) Differs from true starch as don’t turn blue with I2 solution Stored up for future use either scattered in refractile granules in endoplasm or deposited around pyrenoids Paramylum is found more abundantly in well fed individuals 2. Saprozoic In prolonged darkness, Euglena loses its chlorophyll & green color Becomes etiolated (pale or white) yet continues to live & perform all life activities Lives by saprozoic method by feeding on organic matter dissolved in water Euglena secretes digestive enzymes typically like animals Chloroplasts lost in dark retained in light E. gracilis, change is permanent Pinocytosis also seen at reservoir for intake of proteins & other large molecules Respiration Respires free oxygen dissolved in water, diffuses in through pellicle Oxygen brings oxidation reactions catalyzed by enzymes of mitochondria Energy is trapped in high energy phosphate bonds of ATP supplying energy As a result of oxidation reactions, H2O & CO2 are formed by-products In sunlight, CO2 utilized for photosynthesis In dark it is liberated to outside by diffusion through general body surface Osmoregulation & Excretion Osmoregulation: removal of excessive water entering into body by endosmosis carried by anteriorly placed contractile apparatus Outer pellicle permeable to water, so water continuously enters inside Contractile apparatus consists of a large contractile vacuole surrounded by numerous accessory small vacuoles Cytoplasm secretes excessive water into these smaller ones which finally drain into the larger one Larger vacuole empties into reservoir Process involves diastole (increase in volume) & systole (decrease in volume) of large contractile vacuole Diastole: contractile vacuole is filled with water Systole: contractile vacuole emptied to throw watery content into reservoir Excretory substance also excreted by contractile vacuole in reservoir Adjacent wall of contractile vacuole is unstable and bursts at systole Ammonia, passes out by diffusion through general body surface Reproduction No evidence of sexual reproduction Multiples asexually by binary & multiple fissions Encystment 1. Binary Fission Transverse binary fission unknown Under favorable conditions water, temperature & food availability, divides by simple longitudinal binary fission Division symmetrogenic (mirror image) First nucleus divides into 2 by mitosis then division of cytoplasm (cytokinesis) Unusual feature is persistence of nuclear membrane Prophase: all nucleoli fuse together in a single nucleolar body & each chromosome splits into 2 daughter chromatids Metaphase: paired chromatids come to lie in a longitudinal plane Microtubules, present in nucleus, do not form spindle Anaphase: paired chromatids separate & move towards poles Nuclear membrane constricts longitudinally Telophase: constriction of nuclear membrane deepens & finally into 2 daughter nuclei Nucleolar body splits into 2 so each daughter has its own nucleus Next is cytokinesis Longitudinal furrow appears in cytoplasm Begins at anterior end that deepens & finally divides Euglena into 2 daughters Reservoir, cytopharynx, cytostome, flagella, stigma & contractile vacuole duplicate New set of flagella arises from new basal bodies which appear in the vicinity of old basal bodies Multiplication of basal bodies usually precedes cell division 2. Multiple Fission & Palmella Stage Under inactive periods, Euglena undergoes multiple fission in an encysted condition Movement ceases flagellum thrown off & Euglena becomes rounded & embedded in an extensive thick, mucilaginous coat (cyst) Cyst secreted by muciferous bodies Encystment followed by repeated longitudinal divisions with formation of several daughter individuals (16 or 32) embedded within mucilaginous mass Daughter individuals secrete their mucilaginous cysts Resembles palmella stage of Chlamydomonas Later, acquire flagella & escape to grow into adult euglenae 3. Encystment Protective measure Tide over lack of food, O2, excessive heat, drought Thick, yellowish, spherical & gelatinous cyst wall secreted Composed of special carbohydrate Cyst may be thick, stalked or operculated with animal in center Animal withstands adverse conditions & enjoys far dispersal Conditions favorable, becomes active, emerges from cyst, resumes normal freeswimming life May undergo single or several divisions forming 2 or many individuals (palmella stage) Euglena as an Animal Absence of cellulose cell wall overlying plasma membrane Presence of centrioles forming blepharoplasts Reserve food is paramylon, not true starch Presence of paraflagellar body, a sensory (photoreceptive) organelle Moves from place to place like an animal Pinocytosis & probably holozoic nutrition Thank You For Your Patience Your feedback on: navoditageorge@gmail.com