Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET

NEET: Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET

The document Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET is a part of the NEET Course Biology Class 11.
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Introduction

Kingdom of Unicellular Eukaryotes

  • The Kingdom Protista was proposed by Ernst Haeckel (1866)
  • Although all single-celled eukaryotes are placed in Kingdom Protista yet its boundaries are not well defined
  • Phylogenetically the kingdom Protista acts as a connecting link between the prokaryotic kingdom- Monera on one hand and the complex multicellular kingdoms Fungi, Plantae and Animalia on the other hand. 
  • Protists are regarded as ancestors of all multicellular eukaryotic organisms.

Characteristic of Kingdom Protista

  1. Occurrence: Protists are mostly aquatic organisms, therefore, they are found in the sea, fresh water and moist soil. Many protists are found in water bodies in the form of plankton. Some protists live in the bodies of animals as parasites.
  2. Structure: Protists are microscopic organisms. The cell is eukaryotic. It is surrounded by plasmalemma (cell membrane). There may be an outer covering of pellicle, cuticle, shell or cellulose wall. It contains organelles like mitochondria, Golgi complex, endoplasmic reticulum, 80S ribosomes, etc. Centrioles occur in a number of types. Photosynthetic forms contain chloroplasts with internal thylakoids. Cilia and flagella occur in a number of forms. They have typical 9+2 fibrils. The nucleus has a typical structure-porous nuclear envelope, chromatin, nucleolus and nucleoplasm. Many forms have more than one similar or dissimilar nuclei.
    Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET
  3. Locomotion in Protists: Five modes of locomotion are recognized in the Protista: pseudopodial, flagellar, ciliary wriggling and mucilage propulsion.
    A. Pseudopodial Locomotion - It is a slow creeping type of locomotion that is performed with the help of protoplasmic outgrowths called pseudopodia. Pseudopodial locomotion occurs in sarcodines and slime moulds.
    Pseudopodia are of four types: 
    (i) Lobopodia These pseudopodia are lobe-like with broad and blunt ends. These are present in Amoeba. 
    (ii) Filopodia. These pseudopodia are fine, thread-like, tapering, and are composed of ectoplasm. These are found in Euglypha. 
    (iii) Axopodia. These are long and stiff, with hard axial filament. These pseudopodia are present in Actinophrys.
    (iv) Reticulopodia. These are long and branching. The branches of adjacent pseudopodia may form a network. These are found in Globigerina.
    B. Flagellar Locomotion - Flagella show whip-like movement. They usually beat independently. This type of locomotion occurs in dinoflagellates (e.g., Gonyaulax), euglenoids (e.g., Euglena and zooflagellates e.g., Leishmania).
    C. Ciliary Locomotion - Cilia show oar-like movement. All the cilia of a cell show coordinated movements which are of two types, isochronic and metachronic rhythms. In isochronic or synchronous rhythm, all the cilia of a cell beat simultaneously. They do so in rapid succession one after the other in the case of metachronic rhythm. It occurs in ciliates (e.g., Paramecium). Basically, flagella and cilia are identical in structure. However, they differ in some respects as mentioned below.
    Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEETD. Wriggling Locomotion - It is a slow worm-like movement that is performed with the help of a wave of contraction and expansion in the body, e.g., sporozoans, non-flagellates, euglenoids.
    E. Locomotion by Mucilage Propulsion - Some protists like diatoms do not have any organelles of locomotion. They can, however, move from one place to another through the secretion of mucilage. This type of locomotion occurs in the direction opposite to that of mucilage secretion.

Nutrition in Bacteria

Protists have the following modes of nutrition.

1. Photosynthetic (Holophytic) - In this mode, the organ prepares its food from CO₂ and water by utilizing sunlight with the help of photosynthetic pigments like chlorophyll. The process is called photosynthesis. Examples are Dinoflagellates, Diatoms and Euglenoids.

2. Holozoic or Zootrophic(Ingestive Phagotrophic) - In this mode, the individual captures and ingests the food like animals, found in many protozoans like Amoeba and Paramecium

3. Saprotrophic or Saprobic - In this mode, the organism releases enzymes into the surroundings where the enzymes convert organic matter into simpler products. These products are then absorbed through the body surface of the organism. Saprobic nutrition is found in slime moulds.

4. Parasitic - Some protists get their food from the body of other organisms. The individual which obtains its food is called a parasite and the organism from which a parasite gets food is called the host. Trypanosoma, Giardia, Entamoeba, Plasmodium are some examples of parasites. 

5. Mixotrophic - It is a mixed type in which the organism can perform two kinds of nutrition. For example, in Euglena nutrition is both holophytic and saprobic. 

6. Symbiotic - Zooflagellates Trichonympha and Lophomonas live as symbionts in the intestine of termites and wood roaches respectively. Both Trichonympha and Lophomonas secrete cellulose digesting enzymes which convert cellulose into glucose. The digested food (glucose) is shared by both zooflagellates and the hosts. 

7. Pinocytosis - Soluble organic substances and salts are known to be absorbed in Amoeba and others through pinocytosis. 

Respiration in Protists

Most of the free-living protists perform aerobic respiration, however, the parasitic protists and protists living at the bottom of aquatic habitats respire anaerobically.

Reproduction in Protists

They reproduce by both asexual and sexual methods.

(a) Asexual Reproduction. It involves only one parent. All the young ones produced asexually have the same genetic constitution as that of the parent and are called clones. Asexual reproduction can occur in the following ways: 

(i) Binary fission. It is the division of the parent body into two equal daughter individuals by mitosis. Examples: Amoeba, Euglena and Paramecium.

(ii) Multiple fission. It is the division of the parent organism into several daughter individuals. Examples: Amoeba and Plasmodium.

(iii) Plasmotomy. It is the division of the multinucleate protist into two or more multinucleate offspring by the division of cytoplasm without nuclear division. It occurs in Opalina.

(iv) Spore formation. In some protists, spores are formed for asexual reproduction.

Spores have some sort of covering to withstand unfavourable conditions. On germination, each spore gives rise to a new individual. Example: Slime moulds. 

(v) Budding. In budding a small outgrowth develops from the parent body which separates and develops into a new individual. Example Arcella (a Sarcodine)

(b) Sexual Reproduction. It originated in protists: Sexual reproduction involves two fundamental processes; meiosis, which reduces the number of chromosomes from 2n to In and fertilization or fusion of two In gametes to form a 2n zygote (fertilized egg). Meiosis is essential in sexual reproduction since it reduces the chromosome number to half in gametes so that after fertilization the number of chromosomes is kept constant in a species. There are two methods of sexual reproduction.

(i) Syngamy. It is a complete fusion of two gametes to produce a diploid zygote. Syngamy is of three types:
(1) Isogamy (two fusing gametes are similar e.g., Monocystis);
(2) Anisogamy (two fusing gametes are dissimilar, e.g. Ceratium) and
(3) Oogamy (large non-motile gametes are fertilized by smaller motile gametes, e.g., Plasmodium).

(ii) Conjugation. It is a temporary union of two individuals to exchange their haploid pronuclei to form a zygote nucleus. Each individual with a zygote nucleus produces daughter individuals by binary fission. It occurs in Paramecium.

Life Cycles in Protists 

The sequence of events between any given phase in one generation and that similar phase in the next succeeding generation constitute a life cycle. Two types of life cycles are found in protists.

(a) Life Cycle Showing Zygotic Meiosis 

  • It occurs in some dinoflagellates (e.g., Ceratium, Gymnodinium; von Stosch, 1973) and cellular slime moulds. 
  • The zygote is 2n that divides by meiosis (also called zygotic meiosis) and produces vegetative cells with In chromosome number. 
  • These cells divide repeatedly by mitosis and all the resulting daughter cells maintain the 1n a number of chromosomes. 
  • Some of the vegetative cells produce gametes. 
  • When these gametes combine in fertilization, a zygote is formed and the life cycle is completed. 

(b) Life Cycle Showing Gametic Meiosis 

  • This is found in the majority of protozoan protists, diatoms and acellular slime moulds. 
  • The organism spends most of its life cycle in the 2n condition. 
  • The gametes are only In (haploid) that are produced by meiosis (also called gametic meiosis). 
  • The gametes fuse to form a zygote that grows to form the diploid individual.

Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET

Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET

Major Groups of Protists

The kingdom Protista has been broadly divided into three main groups.

A. Photosynthetic Protists (Protistan Algae).

B. Consumer-Decomposer Protists (Slime Moulds) 

C. Protozoan Protists

A. Photosynthetic Protists (Protistan Algae)

Photosynthesis takes place in these protists. They constitute the main portion of the phytoplankton. The phytoplankton is green photosynthetic organisms that are passively drifted by the water current. They include dinoflagellates, chrysophytes and euglenoids.

(1) Dinoflagellates

  • They are a group of about 1,000 species of photosynthetic protists. 
  • The dinoflagellates belong to the division pyrrophyta and class dinophyceae.

Characteristic Features of Dinoflagellates

A. Habitat and Habits. 

(i) The dinoflagellates are an important component of phytoplankton. Most of them are marine but some occur in freshwater. Some dinoflagellates such as Gymnodinium and Gonyaulax grow in large numbers in the sea and make the water look red and cause the so-called "red tide"

(ii) Some periplast covered golden dinoflagellates called zooxanthellae occur in a number of marine protozoan protists (ciliates, radiolarians, foraminiferans) and invertebrates (sponges, corals, jellyfishes, gastropods, etc.). 

(iii) Some marine dinoflagellates show bioluminescence. It means they emit light, e.g. Noctiluca, Gonyaulax, Pyrocystis, Pyrodinium. 

(iv) Nutrition is photosynthetic.

B. Structure. 

(i) Dinoflagellates are basically unicellular motile and biflagellate, golden brown, photosynthetic protists. The predominant colour is golden brown but yellow, green, brown and even blue forms also occur due to change in the proportion of various pigments. A few are nonmotile, non-flagellate, amoeboid, filamentous. 

(ii) Cells are generally covered by a rigid coat the theca or lorica of articulated and sculptured plates of cellulose. Periplast may occur instead of the theca. Because of the presence of sculptured plates, these protists are often known as armoured dinoflagellates. (iii) The theca contains two grooves, the longitudinal groove called the sulcus and the circular groove known as the cingulum or annulus or girdle. 

(iv) The two flagella are different (heterokont), one transverse flagellum and another longitudinal flagellum. The longitudinal flagellum is narrow, smooth, directed posteriorly and lies in the sulcus. The transverse flagellum is ribbon-like and lies in the cingulum or annulus. The two types of flagella beat in different directions. This causes spinning dinoflagellates while swimming in water. 

(v) The nucleus is larger in size and has been marked as mesokaryon by Dodge (1966). Chromosomes do not have histone or RNA. 

(vi) Plastids or chromatophores have chlorophyll a and chlorophyll c

(vii) Mucilage bodies or vesicles occur below the cell membrane. 

(viii) A noncontractile vacuole called pusule is present near the flagellar base. Pusule may take part in floatation and osmoregulation. Contractile vacuoles are absent. 

(ix) Varieties of eyespots occur in dinoflagellates. Some of them are like ocelli. 

(x) Trichocysts are found in a number of dinoflagellates. Nematocysts have also been reported in a few dinoflagellates.

C. Reserve Food. 

Reserve food is stored in the form of starch and oils. 

D. Reproduction. 

(i) Asexual reproduction is commonly through cell division. Cysts occur in a number of dinoflagellates. 

(ii) Sexual reproduction has been reported in some dinoflagellates (e.g., Ceratium). It is isogamous and anisogamous. 

(iii) The life cycle involves zygotic meiosis in Ceratium, Gymnodinium and Woloszynskia. Gametic meiosis occurs in Noctiluca.

Examples. Glenodinium, Peridinium, Gymnodinium. Gonyaulax,Ceratium, Noctiluca.

Economic Importance of Dinoflagellates 

  • Some dinoflagellates (e.g.. Gonyaulax catenella) are poisonous to vertebrates. 
  • When they are in large number, they produce the toxin called saxitoxin into the seawater which kills fishes and other aquatic animals. 
  • Marine shellfishes (sea mussels-molluscs) eat a large number of dinoflagellates. 
  • The poisonous substance of dinoflagellates reaches the shellfish. 
  • The poison is not harmful to the shellfishes but the consumption of these infected mussels by man causes a severe illness called paralytic shellfish poisoning (PSP) and may be fatal.

(2) Chrysophytes

Chrysophytes include diatoms and desmids. They belong to the division Chrysophyta/Bacillariophyta.

(i) Diatoms

A. Habitat and Habits. 

(i) Diatoms occur in all aquatic and moist terrestrial habitats. 

(ii) They may be free-floating or bottom dwellers. The free-floating forms remain suspended on the surface of the water by mucilage secretion and the presence of lightweight lipids. 

(iii) Diatoms may show gliding type of movement with the help of mucilage. 

(iv) 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. It may extend for several hundred metres from where the same can be mined.

B. Structure. 

(i) The body is covered by a transparent siliceous shell (silica deposited in the cell wall) known as a frustule. The frustule is made of two valves, epitheca and hypotheca. The two valves fit together like a soapbox. The frustule possesses very fine markings, pits, pores and ridges. 

(ii) Diatoms are microscopic, variously coloured and of diverse forms protists that do not possess flagella except in the reproductive state. 

(iii) They are basically unicellular but can form pseudo-filaments and colonies. 

(iv) Depending upon the symmetry, the diatoms are of two types namely, pennate and centric. The pennate diatoms show bilateral symmetry e.g., Navicula and the centric diatoms have radial symmetry, e.g., Melosira

(v) Each cell has a large central vacuole. The single large nucleus is commonly suspended in the central vacuole by means of cytoplasmic strands. 

(vi) Chloroplasts or chromatophores are yellowish-brown to greenish-brown. They contain chlorophyll a and chlorophyll c. 

(vii) Diatoms contain fucoxanthin (typical of brown that provides a brownish tinge)

Soap-box like appearance of Diatoms Soap-box like appearance of Diatoms C. Reserve food. 

The food is reserved in the form of oils and leucosin (polysaccharides). Volutin globules (proteinaceous in nature) are also present. 

D. Reproduction.

(i) The common mode of multiplication is by binary fission. 

(ii) Resting spores or statospores are formed in some cases. 

(iii) Meiosis. is gametic. Sexual reproduction varies from isogamy to oogamy. In the latter case, male gametes are motile and uniflagellate. Fertilization produces a zygote that grows in size and forms a rejuvenascent cell called auxospore. in that their vegetative cells are typically diploid.

(iv) Diatoms are, unusual

Examples. Triceratium, Pleurosigma. Navicula, Cymbella, Amphipleura. 

Economic Importance of Diatoms 

(1) Diatoms are very important photosynthesizers. About half of all the organic matter synthesized in the world is believed to be produced by them. Though microscopic, diatoms are an important source of food to aquatic animals. A 60-tonne blue whale may have 2 tonnes of plankton in the gut which is mostly diatoms. 

(2) The oils extracted from some fishes and whales are actually the ones produced by diatoms. 

(3) Diatomite deposits are often accompanied by petroleum fields. Much of the petroleum of today is probably due to decayed bodies of the past diatoms. 

(4) Diatomite is porous and chemically inert. It is, therefore, used in the filtration of sugar, alcohols oil, syrups and antibiotics. 

(5) Diatomite is employed as a cleaning agent in toothpaste and metal polishes. 

(6) Diatomite is added to paints for enhancing night visibility

(7) Diatomite is employed as insulation material in refrigerators, boilers and furnaces. 

(8) Diatomaceous earth is added to make soundproof rooms

(9) Diatomite is a good industrial catalyst. 

(10) Diatomite is a source of water glass or sodium silicate

(11) Diatoms are very good pollution indicators.

(ii) Desmids.

  • Desmids are unicellular green algae. 
  • Like Spirogyra, they have an elaborate chloroplast. Their cells have two distinct halves. The outer wall of the cell has various protuberances covered with a mucilaginous sheath which is thought to play a role in the cell's slow gliding movement. 
  • Sexual reproduction occurs by 'conjugation' similar to that of Spirogyra. They are mainly found in fresh water and are usually indications of clean (unpolluted) water.
The document Kingdom Protista: Chrysophytes and Dinoflagellates Notes | Study Biology Class 11 - NEET is a part of the NEET Course Biology Class 11.
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