Protista : It is a kingdom of aquatic unicellular, eukaryotic micro organisms structure of Protista.
(i) These are having a typical eukaryotic structure with a membrane bound nucleus.
(ii) The cytoplasm of this kingdom has number of membrane bound organelles like mitochondria, golgi complex, endoplasmic reticulum, chloroplasts etc.
(iii) Some protista for locomotion have flagella or cilia.
(iv) The photosynthetic protista have a cell wall.
(v) Many protozoa which falls in the category of protista have holozoic nutrition and hence have elaborate organelles for ingestion, digestion and egestion.
Locomotion in Protists : Flagella, Cilia and Pseudopodia are responsible for the locomotion of protists.
(i) Flagella : Flagella are long, whiplike, fine structures which help organisms to locomote. Euglena has only one flagellum while others may have more than one.
(ii) Cilia : Cilia are short, fine, hair like structures present all over the body of protist. Their locomation is in a coordinated manner to bring about the movement. With the help of these, ciliates move rapidly, they can turn, tumble and even reverse. Ciliates are considered to be the fastest predatory protists. e.g., Paramaecium.
(iii) Pseudopodia : Pseudopodia are kind of false feet. These are blunt protoplasmic extensions which gives an irregular shape to the organisms and help in the locomotion by getting extended in a particular direction. e.g., Amoeba.
Reproduction in protists : Both asexual and sexual modes of reproduction are shown by these organisms.
Cyst formation : Cyst formation is a means of saving a cell from unfavourable conditions like drying up of a pool of water. This is not a mode of reproduction.
Photosynthetic Protists (The Protist Algae) : Photosynthetic protists are algae. This kind consists of a number of phyla. The group algae is divided on the basis of the
(i) kind of colouring material
(ii) compounds used for storage and
(iii) details of the reproductive cycle.
Algae are many types of aquatic photosynthetic organisms. These range from microscopic forms to giant weeds. The term algae is referred in Kingdom Monera is used for blue-green algae or cyanobacteria.
Kingdom Protista is used for phytoplanktonic organisms.
Kingdom Plantae is used for red, green or brown algae.
Phylum Pyrrophyta
Important features
(i) These are unicellular, motile, photosynthetic organisms.
(ii) Their body is enclosed in a cellulose wall divided into plates which give an armoured appearance.
(iii) They have two unequal flagella; one lies in a longitudinal direction and the other lies transversely in a furrow between the wall plates.
(iv) These organisms reproduce asexually only.
(v) Most of the species are sea living. Scientist know about 1,000 species.
Chrysophyta
Important Features
(i) Most of them occur as individual cells. They are attached to each other to form a colony.
(ii) These organisms are unique because they have deposits of silicon dioxide in their cell wall. When the organism dies everything disappears except silicon dioxide.
(iii) Pairs of glassy cell walls are arranged like a small dish with a cover or soap box. The glassy walls are decorated with grooves and holes.
(iv) They do not have flagella and float due to light storage lipids.
(v) They undergo asexual reproduction and each daughter cell retains one half of the old wall and synthesises a new half.
(vi) During sexual reproduction, they form gametes to reproduce.
Phylum Euglenophyta
Important features
(i) This phylum is unicellular and free living. They are found in fresh water ponds, ditches or in damp soil.
(ii) They do not have cellulose cell wall but have a pellicle. Pellicle is flexible and allows a change in shape.
(iii) Flagella helps Euglena to pull through the water. Flagella is long, whip-like and inserted at the end in a cavity.
(iv) Have a light sensitive red spot called Eye spot near the flagellum base. This enables it to move towards or away from light.
(v) The dominant photosynthetic pigment is chlorophyll, because of it they appear green in colour.
(vi) Store carbohydrate as paramylum (similar to starch).
(vii) Asexual reproduction is by longitudinal fission starting at the flagellar end. The flagellum duplicates before the cell divides.
(viii) They form cysts during unfavourable conditions.
Phylum (Myxomycophyta)
(i) Acellular Slime Mould e.g., Physarum. It appears like one large mass of protoplasm in which there may be thousands of nuclei. They do not have cell walls. It is called plasmodium and often appears as a slimy, fan shaped network of living matter. This mass flows along in an amoeboid manner on the soil of a forest, surface of dead leaves or on a rotting log. On moving along it engulfs food particles and digests them in food vacuoles.
(ii) Cellular Slime Mould e.g., Dictyostelium. In cellular slime mould numerous individual, amoeboid cells aggregate and move together like a mass of protoplasm. This is called as a pseudoplasmodium since individuals are not fused.
Protozoan protists
Protozoan Protists are unicellular or acellular microscopic organisms possessing typical cell structure.
These are acellular, microscopic, single celled with typical cellular structrues.
General characteristics
1. Small usually microscopic but can be seen with naked eyes.
2. Body : Body is acellular having one or more than one nuclei.
3. Symmetry : Non-symmetrical, bilateral, radial, spherical.
4. Body covering : A pellicle.
5. Shape : Usually constant.
6. Division of labour : No physiological division of labour hence acellular.
7. Locomotion : Pseudopodia, flagella (whip-like) and cilia (hair like) or organs absent.
8. Nutrition : Holozoic, holophytic, parasitic or saprozoic.
9. Excretion : Through contractile vacuoles or generally through body surface.
10. Reproduction : Asexually and sexually.
11. Life histories : Often complicated by alternation of generation.
12. Encystment : Helps in dispersal and resist unfavourable condition.
13. Habit and habitat : These are ubiquitous or cosmopolitan. Free living protozoans mainly live in seas or fresh water. Several protozoans are commensal, symbiotic and parasitic species. Parasitic protozoans are internal or external.
Most protozoans are free living but some are colonial also.
Most protozoans feed upon the organic food matters. Some are meat eaters who feed on the other protozoans. Some feed only upon plants. Most of them feed upon dead or decaying organic matters and parasitic forms live upon the tissues of hosts whereas other species are synthesizing their own food with the help of chlorophyll.
Classification : This group on the basis of presence or absence of locomotory organs is divided into five classes.
Phylum 1
Sarcodina—Includes 80,000 sps.
1. Body : Naked.
2. Locomotion : By temporary pseudopodia.
3. Excretion : Usually with contractile vacuoles.
4. Most of them are free livings.
e.g. Amoeba, Entamoeba, Arcella, Polystomella.
Phylum 2
Mastigophora or flagellata—2000 sps.
1. Body : Covered with thin pellicle.
2. Locomotion : By whip-like undulating flagella.
3. Habit : Free living and solitary. Some are parasitic.
e.g. Cryptomonas, Euglena, Chlamydomonas, Volvox, Noctiluca, Ceratium, Trypanosoma, Leishmania, Giardia.
Phylum 3
Sporozoa—2000 sps
1. Body : Covered with thick cuticle or pellicle.
2. Locomotion : Absent.
3. Mouth and cytopyge (anal opening): Present.
4. Spore formation : During sexual reproduction spores are formed.
5. Habit : Exclusively parasitic and degenerated.
e.g. Monocystis, Gregarina, Coccidium (eimeria) Plasmodium.
Phylum 4
Ciliata—2500 sps.
1. Body : Naked and bound by a firm pellicle externally.
2. Locomotion : Large number of hair like cilia.
3. Mouth and cytopyge : Along with oral apparatus.
4. Nuclei : Micro and Macro are two types of nuclei.
e.g., Opalina, Paramecium, Balantidium, Vorticella.
Amoeboid : It moves and engulfs prey with pseudopods and movement is amoeba-like.
Diatom : It is a golden brown algae and a fresh water or marine unicellular.
Plankton : Fresh water or marine organisms suspend near the surface of water.
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