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  1. KINGDOM MONERA
  2. These are the oldest, simplest and most numerous microorganisms.

    They are distinguished by the following characteristics:

    I. They are prokaryotes.

    II. They are mostly unicellular, but may be in the form of colonies or filaments of independent cells.

    III. Their mode of nutrition is mainly absorptive, but some are photosynthetic or chemosynthetic.

    IV. They are usually nonmotile, but some may have flagella and gliding movements. Cilia are absent.

    V. Their reproduction is primarily asexual, by fission.

    Monera includes heterogenous microorganisms including archaebacteria, eubacteria, actinomycetes and cyanobacteria.

    (a) Archaebacteria : (Archaeos : old)

    (ii) Sulphur- dependent bacteria : These are aerobic bacteria which convert sulphur either into sulphuric acid (H2SO4) or into hydrogen sulphide (H2S). Hence, they are present in hot sulphur springs. They can tolerate highly acidic pH (pH=2) and high temperature (about 80o C). Hence, they are also called thermoacidophiles.

    Examples: Thermoplasma, Sulfolobus

    (b) Eubacteria (Eu: true):

    These are "true" bacteria ubiquitous in nature, i.e. they are found practically in all the environments, at all the attitudes and depths, in extremely low and high temperature, in fresh as well as in marine water and in bodies of plants and animals both living and dead. In fact, it is difficult to name any place where bacteria are not found. They show the following general characters:

    Locomotion : They are generally non-motile, but motile bacteria may have flagella at one end, at both ends, or all around the cell.

    Cell structure : Their cell wall contains peptidoglycan and muramic acid.

    Their cytoplasm is without streaming movements and without endoplasmic reticulum. However, free ribosomes are present.

    Mitochondria are absent but respiratory enzymes are located on the surface of mesosomes which are invaginations of plasma membrane.

    Golgi complex and true plastids are absent. However, photosynthetic bacteria show chromatophores containing bacteriochlorophyll (e.g. purple-S-bacteria) or chlorobium chlorophyll (e.g. green-S-bacteria).

    All three types of RNA are present.

    Cells are prokaryotic, i.e. without nuclear membrane, nucleoplasm and nucleolus. They contain a single molecule of circular double stranded DNA attached to the plasma membrane at one point.

    Respiration : They are aerobic or anaerobic.

    Nutrition : They show autotrophic or heterotrophic mode of nutrition. Autotrophic bacteria are of two types, viz., photosynthetic, which produce food material by using light energy (e.g. purple-S-bacteria and green-S-bacteria), and chemosynthetic which produce food material by using chemical energy which is derived by oxidizing certain inorganic compounds (e.g. Nitrosomonas, Nitrobacter). Heterotrophic bacteria are saprophytic, growing on dead and decaying organic matter, or parasitic, growing in living plants and animals, including humans. The parasitic bacteria may be pathogenic, causing diseases (e.g. Xanthomonas citri, Diplococcus pneumonae) or non-pathogenic, which usually form a symbiotic association with their hosts (e.g. Rhizobium, fixing nitrogen in leguminous plants, and cellulose-digesting bacteria in ruminant stomachs).

    Staining : Those bacteria which retain Gram stain are called gram-positive bacteria, (e.g. Streptococcus) while those which do not retain the stain are called gram-negative bacteria, (e.g. Escherichia coli).

    Reproduction : They reproduce both asexually as well as sexually. Asexual reproduction is by binary fission which takes place in favorable conditions, or by endospore formation, which takes place in unfavorable conditions. Sexual reproduction is by conjugation.

    Economic importance : Bacteria act as both friends and foes of mankind as described below:

    Useful activities

    (i) They increase the fertility of soil by converting atmospheric nitrogen into nitrates (nitrogen fixation), by converting ammonia derived from dead bodies into nitrates (nitrification) or by decomposing dead organic matter and forming humus which is the most fertile part of the soil.

    (ii) They form symbolic association with man and animals and help in digestion.

    (iii) In industry they are used in ’curdling’ of milk, ’retting of fibers’ of jute and hemp’curing’ of tea and tobacco leaves ’tanning’ of leather, production of vinegar, etc.

    (iv) They are used in the production of certain antibiotic drugs.

    (v) They are scavengers of nature and help to keep the environment clean and also play an important role in recycling of nutrients in nature.

    Harmful activities

    (i) They cause dreadful diseases in plants, animals and human.

    (ii) They spoil milk, meat, fish and vegetables.

    (iii) Some of them release toxins into spoiled food and cause food poisoning.

    (iv) Denitrifying bacteria reduce fertility of soil by converting nitrates into free nitrogen (denitrification).

    (c) Actinomycetes (Actinos = rays)

    These are prokaryotes showing characters similar to both bacteria and fungi. Like fungi, they show filamentous bodies and they reproduce by forming conidia in chains. However, like bacteria, their cell wall is made up of peptidoglycan and not of chitin or fungal cellulose. The nucleus is without a nuclear membrane, and sexual reproduction is totally absent. They are regarded as intermediate between fungi and bacteria; but because of the thin filamentous structure, they are classified with bacteria. They may be aerobic or anaerobic, saprophytic or parasitic.

    (d) Cyanobacteria

    These were formerly known as blue green algae because of their filamentous nature. They are photosynthetic autotrophs widely distributed in nature. They are found in ponds, lakes, moist soils, logs of wood, ocean and even in hot water springs.

    Structurally they are similar to Monera in that they have no nuclear membrane and no membranous organelles like mitochondria and chloroplasts. They contain chlorophyll and internal membranes called photosynthetic lamellae or thylakoids. Besides, they also contain pigments phycocyanine (blue) and phycoerythrin (red), which are modified to produce brown, purple, yellow, blue or even red-coloured individuals. They are unicellular or colonial forms which are round, rod-shaped or filamentous. The cell wall is made up of peptidoglycan covered by a characteristic gelatinous envelope. Some cells in the filament are colorless and are called heterocysts which fix free atmospheric nitrogen. The fragmentations take place at these points. They are devoid of flagella but some move by peculiar gliding movement. Food is often stored in the form of oil or glycogen droplets. Some can stand extremes of temperature and pH. The method of reproduction is by binary fission. Since they reproduce extensively, they often become dominant microorganisms in the polluted water of lakes and ponds containing a rich supply of organic matter, forming huge populations often called "blooms". The periodic redness in the oceans is due to blooms of red cyanobacteria. Common examples are Anabaena, Nostoc, Oscillatoria, etc.

    Economic importance : Cyanobacteria have the following economic importance :

    (i) Heterocyst-bearing forms perform the function of nitrogen fixation. Hence, they are used as biofertilizers in paddy field, to increase yield.

    (ii) Non-toxic forms like Spirulina are cultured in large tanks as protein-rich animal feed.

    (iii) Nostoc is cultured and used as feed for aquatic animals.

    (iv) Some forms like Anabaena and Nostoc make the drinking water poisonous, which can cause death of cattle, birds and even humans. These forms may even interfere with water filtration systems.

    Role of Monera

    1. Role in cycling : Monera are chiefly decomposers concerned in cycling, rotation of metabolites like carbon, hydrogen, nitrogen, and sulphur . in nature. Life on earth would have run out were it not for the decomposition of dead matter by bacteria and release of the elements for resynthesis of cellular compounds. This cyclic journey of chemical elements from biological organisms (bio) through soil or earth crust (geo), is referred to as the biogeochemical cycle.

    2. Role in symbiosis : Some forms show symbiotic relationship such as Rhizobium in the roots of leguminous plants or Nostoc and Anabaena in coralloid roots of Cycas, which fix free atmospheric nitrogen into nitrates, and Escherichia coli which inhabit the colon of the human intestine and help in synthesizing Vitamin B.

  3. Pathogenic forms : Some Monera are also pathogenic, producing common diseases like typhoid, cholera, diphtheria, tuberculosis and pneumonia in human beings.

List of common bacterial diseases in man

No.

Disease

Causative agents

1

Dysentery

Shigella dysenteriae

2

Cholera

Vibrio cholerae

3

Diphtheria

Corynebacterium diphtheriae

4

Pneumonia

Diplococcus pneumoniae

5

Tuberculosis

Mycobacterium tuberculosis

6

Tetanus

Clostridium tetani

Broad control measures : The broad control measures are as follows:

(i) Use of disinfectants : These are strong chemicals which are distributed where bacteria thrive and multiply. Some common disinfectants used are bleach, phenol, and H2O2 peroxide.

(ii) Use of antiseptics : These are mild chemicals which are locally applied to kill bacteria, such as alcohol and iodine.

(iii) Use of antibiotics : These are specific drugs which are used to prevent the growth of bacteria. Some common antibiotics are tetracyclin, streptomycin, penicillin, neomycin and erythromycin.

(iv) Sterilization : This is the common method by which bacteria are killed by excessive heat or ultraviolet irradiation, which disrupts and destroys the protiens and nucleic acids in the bacteria.

Hot water springs

Hot water springs also called thermal springs are flows of hot water originating from active volcanic rock. The temperature of hot water is about 85o C. This water contains minerals (bicarbonates of calcium and magnesium) dissolved from the rock. At this temperature only certain bacteria like Thermus, Sulpholobus, Bacillus and some cyanobacteria can survive. Hence, these organisms are called thermophiles. Many times hot water springs contain sulfur. Hence, taking bath in such water is remedy for skin diseases in humans.

Kingdom : Protista

(Eukaryotic unicellular organisms)

Protista includes all eukaryotic unicellular microorganisms, either plant-like or animal-like or showing overlapping characters of both plants and animals. Primarily they are aquatic and widely distributed all over the world, occurring in oceans, lakes, ponds and damp soils. They are autotrophic or heterotrophic. The latter are free-living or parasitic on or within multicellular organisms. Thus it reflects the lifestyles either of plants, animals or fungi. Phylogenetically they serve as the connecting link between prokaryotic Monera and complex multicellular kingdoms of plants fungi and animals. They are distinguished by the following characteristics:

(i) They are first eukaryotes, having a well organized nucleus and complex membranous organelles.

(ii) They are unicellular or colonial forms without distinct division of labor.

(iii) They are autotrophic or heterotrophic showing varieties of metabolic systems.

(iv) Locomotion is by pseudopodia, flagella or cilia.

(v) They show mitosis, meiosis and simplest type of sexual reproduction for the first time. Common examples are Ameba, Paramecium, Euglena, diatoms and dinoflagellates.

Kingdom : Plantae

Kingdom Plantae includes all organisms which are truly multicellular and photosynthetic exept for algal protists. They are complex autotrophs preparing food material by photosynthesis for themselves as well as for rest of the other organisms. Hence, they are the chief producers of the world. They are found in all the types of environment: aquatic algae, amphibian mosses, and terrestrial ferns and seed-bearing plants.

The plantae are distinguished by the following characteristics:

(1) They are multicellular organisms, adapted to carry on photosynthesis, hence autotrophic.

(2) Presence of cell wall of true cellulose, enclosing cytoplasm with large vacuoles.

(3) They perform photosynthesis due to chlorophyll present in chloroplasts.

(4) They may show alternation of sexual and asexual generations in life-cycle.

(5) They are non-motile, without definite size and shape.

(6) Growth in these plants is intermittent.

ALGAE

Algae are chlorophyll-bearing unicellular or multicellular plants. When multicellular, they may be colonial or filamentous. Most of them are aquatic, either fresh water, (Volvox), or marine, (Spirogyra). Some are sheet-like (e.g., Ulva). Chlorophyll is present in chloroplasts, the number and shape of which are characteristic of each alga. Besides chlorophyll, they also show various carotenoid pigments which impart different colors to algae. According to the nature of photosynthetic pigments, they are further classified into three divisions such as Chlorophyta (green),. Phaeophyta (brown), and Rhodophyta (red).

Green algae (Chlorophyta)

These algae live in wide variety of habitats, marine to fresh water to damp soil.

General Characteristics

(i) These are unicellular (Chlamydomonas), colonial (Volvox) or filamentous. When filamentous they are unbranched (Spirogyra, Ulothrix) or branched (Chara).

(ii) The cell wall consists of an inner layer of cellulose and outer layer of pectic compounds and may be covered by a gelatinous sheath.

(iii) The protoplasm is divisible into cytoplasm and nucleus. Cytoplasm contains one or more vacuoles. Chlorophyll is present in chloroplasts, the shape and number of which are characteristic of each alga.

(iv) Pigments chlorophyll-a and chlorophyll-b are predominant. However, carotene and xanthophyll are also present.

(v) Food reserve is in the form of starch surrounding the proteinaceous refractile bodies called pyrenoids.

(vi) Reproduction is vegetative by mitotic cell division in unicellular forms or by fragmentation in filamentous forms; asexual by formation of spores such as zoospores, aplanospores, hypnospore and akinates and sexual simply by conjugation or by gamete formation by isogamy or anisogamy or oogamy.

(vii) The life-cycle is of haplontic type showing alternation of dominant haploid stage with short-lived diploid stage.

Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Ulva etc.

Economic importance : Algae are of certain economic importance to man. Chlorophyta serve as initial food producers and the first link in the aquatic food chain, both fresh water and marine. Some like Ulva and Chlorella are used as vitaminized food.

Evolutionary significance : It is believed that chlorophyta has evolved from some flagellate unicellular ancestors like Chlamydomonas. These ancestors, during evolution, gave rise to complex filamentous forms which supposed to have given rise to land plants like bryophytes.

Brown algae (Phaeophyta)

These are multicellular, simple, filamentous or plant-like giant forms called kelps (sea weeds). These are mostly marine, found in cool shallow water.

General Characteristics

(i) The body is the multicellular thallus showing the highest degree of differentiation. The unicellular colonial forms are absent. Some brown algae called kelps or sea weeds exhibit giant forms extending over 50 meters in length and showing parenchymatous organization.

(ii) The cell wall is made up of two layers. The inner firm layer is of cellulose while the outer layer is gelatinous containing compounds like algin, fucosin etc.

(iii) The cytoplasm show one or many vacuoles and single large, distinct nucleus, with one or more nucleoli. Chloroplasts are either discoidal or band-shaped, without pyrenoids.

(iv) Yellow-brown pigment fucoxanthin a type of xanthophyll is predominant which gives golden - brown color to algae, while other pigments such as chlorophyll-a and chlorophyll-b are also present.

(v) The reserved food is in the form of soluble carbohydrates called laminarin and mannitol.

vi) Reproduction is vegetative by fragmentation, asexual by formation of haploid or diploid zoospores and sexual by gamete formation, by isogamy, anisogamy or oogamy.

(vii) The life-cycle shows isomorphic alternation of generations where the gametophyte and sporophyte are morphologically similar (e.g., Ectocarpus), heteromorphic alternation or generations where the gametophyte and sporophyte are morphologically differentiated (e.g. Laminaric) while in there is no alternation of generations as gametophytic generation represented only by gametes.

Examples: Fucus, Sargassum, Laminaria, Ectocarpus etc.

Economic importance : "Komba", a product made from Laminaria, is widely used as food in Japan and oceanic islands. It is boiled with fish, meat or in soups or as a cooked vegetable. A gel called algin, obtained from Macrocystis, Laminaria, etc., is used in the preparation of toothpastes, ice-cream, etc. Sea weeds like Sargassum are used as a directory source of iodine and bromine.

Evolutionary significance : The universal appearance of motile gametes probably suggests that Phaeophyta took its origin from unicellular brown, flagellated ancestors. These do not seem to be related to green algae because of the multicellular vegetative body and presence of fucoxanthin and laminarin which belong exclusively to this group.

Red algae (Rhodophyta)

These are exclusively marine, found in deep waters attached to rocks.

General Characteristics

(i) These are always multicellular, filamentous, radially symmetrical or compressed forms. There is no true parenchymatous construction.

(ii) The cell wall is made up of two layers. The inner one is of cellulose while the outer one is of pectic compounds with mucilaginous envelope.

iii) The cytoplasm is uninucleate and shows a central vacuole. The chromatophores are with naked pyrenoids.

(iv) The pigments are chlorophyll-a, chlorophyll-b, carotene and xanthophyll. However, the green color of chlorophyll-a is masked by red pigment, phycoerythrin and blue pigment phycocyanin.

(v) Food is stored in the form of chemically distinctive starch called floridean starch.

(vi) The reproduction is vegetative by fragmentation, asexual by non-flagellated, haploid carpospores, monospores or tetraspores, and sexual by formation of non-flagellate, non-motile male gametes and an egg, thus oogamous.

(vii) The life-cycle shows either haploid forms or regular alternation of generations between similar haploid and diploid stages.

Examples: Agardhiella, Palysiphonia, Batrachospermum, Gracilaria, etc.

Economic importance : The gelatinous substance extracted from red algae (Gelidium, Gracilaria) is used to prepare agar as a medium for bacterial and fungal cultures, in preparation of ice-cream, jelly, cosmetics, medicines, etc. in Japan. Agar is also used in printing and dying processes in textile industry. Some species (Porphyra) are used as food.

Evolutionary significance : It appears that this group has taken its origin from some unicellular, non-ciliate ancestor as it shows non-flagellated spores and gametes.

Economic importance of algae : Algae are of certain economic importance to mankind. They serve as initial food producers and the first link in the aquatic food chain, both fresh water and marine. Some of the fresh water algae and sea-weeds are used as vitamin-rich food. Brown algae contain iodine and algin. Some red algae are the source of agar jelly, used in the preparation of ice creams and culture media. However, algae sometimes cause contamination of water and some of them release many toxic substances killing millions of fish and other animals drinking this water.

BRYOPHYTA

These are terrestrial non-vascular plants which still require moist environment to complete their life-cycle, hence they are called amphibians of the plant kingdom. Bryophytes show advances over alga by developing special sex organs like antheridia (male) and archegonia (female) and show distinct alternation of generations. Bryophyta are the simplest of land plants, and include mosses, liverworts and hornworts.

They are distinguished by the following characteristics:

(1) They are small terrestrial plants.

(2) They are without a distinct root system but attached to substratum by rhizoids.

(3) They do not posses true vascular tissue.

(4) Sex organs are multicellular with a protective jacket layer.

(5) Gametophyte is dominant and independent.

(6) Sporophyte is small and parasitic or semiparasitic on the gametophyte.

(7) They show a distinct alternation of generations.

External Morphology : Since bryophytes lack efficient conducting tissue, they do not become very large. They are small plants forming green velvety patches on moist substratum. They are green due to presence of chloroplasts. The plant body is either thallus or distinguished into stem-like and leaf-like structures. They are attached to the substratum by rhizoids.

Role of bryophytes in nature :

(i) Bryophytes provide food for herbivores, birds and other animals. (ii) Bog mosses and peat mosses are used as water absorbing and water retaining material in seed beds and green houses. (iii) They are also used as shock absorbing (packing) material for shipment. (iv) Dead and decaying mosses form humus which increases fertility of soil.

Kingdom : Fungi

The fungi are non-green plant-like organisms which are universal in their distribution. They grow in dark and moist habitat and the substratum containing dead organic matter. Mushrooms, molds and yeast are common examples of fungi.

Fungi are distinguished by the following characters:

(1) They have a definite cell wall made up of fungal cellulose.

(2) They are without chlorophyll, hence they are heterotrophic.

(3) They are usually non-motile.

(4) They reproduce mostly by spore formation. However, sexual reproduction may also take place.

Structure: The plant body is unicellular or multicellular. When multicellular, it is composed of profusely branched, interwoven, delicate, thread-like structures called hyphae, collectively called mycelium. Hyphae may be aseptate or septate. When aseptate they are coenocytic, containing many nuclei.

Fungi are heterotrophic in nutrition i.e., they may be saprophytic, (living on dead organic matter) or parasitic (subsisting on other living organisms). The parasitic forms may be ectoparasite, living on the body of the host, or endoprasitic, living inside the body of the host. Some forms are symbiotic.

The fungi are classified as follows:

1. Class : Zygomycetes (lower fungi)

These are filamentous fungi which are terrestrial growing on moist, dead organic matter. They are mainly distinguished by the following characteristics :

Reproduction : Mucor reproduces asexually as well as sexually. Asexual reproduction takes place by formation of non-motile spores and sexual reproduction takes place by conjugation of similar gametes (isogametes).

During asexual reproduction, mycelium gives out upright vertical hyphae called sporangiophores. As the growth proceeds, the tip develops a globular structure called sporangium. At maturity the sporangium breaks open and liberates the spores. On germination, each spore develops into a new mycelium.

Sexual reproduction is isogamousas: it involves the conjugation of two similar gametes. During conjugation the two hyphae regarded as having positive and negative strains come closer (heterothallism). The conjugating hyphae give out club-shaped progametangia which release the terminal part (called gametangia). The gametangia fuse, the middle wall is dissolved and the nuclei fuse in pairs, thus forming a zygote. The latter develops a thick resisting wall to form a zygospore. Each zygospore, on germination, gives out promyucelium which develops sporangium at its tip. When the sporangium ruptures, the spores are liberated and germinate to produce new mycelia.

2. Class : Ascomycetes (higher fungi)

These are also called sac fungi distinguished by the following characteristics:

(I) Mycelium with septate hyphae.

(ii) Asexual reproduction by conidia is a common feature. They are produced at the apex of the hyphae called conidiophores.

(iii) Sexual reproduction occurs by producing sac-like structures called asci, each with usually 8 ascospores, produced endogenously.

Economic importance : Yeast is used for the production of alcohols in brewery, in production of vitamin B, and for raising bread. Claviceps is used to extract an alkaloid called ergotin which is used in medicine. LSD is also extracted from an ergot fungus. Some ascomycetes like Morchella are edible. Neurospora has been used recently for genetic and biochemical research. Some ascomycetes cause severe plant diseases.

Class: Basidiomycetes (higher fungi)

These are also called club - fungi distinguished by the following characteristics:

(I) Mycelium with septate hyphae.

(ii) Asexual reproduction is uncommon.

(iii) During sexual reproduction mycelium develops enlarged reproductive, club-shaped structure called a basidium, hence the name.

(iv) Each basidium produces 4 basidiospores at the tip outside (exogenously),unlike ascospores which develop within the ascus..

(v) In some fungi like mushrooms, a multicellular, complex, fruiting body called a basidiocarp is formed which is often open, sometimes closed. (Basidiocarp = basidia bearing body).

Economic importance : Some mushrooms are used as food for their delicacy and high nutritive value. Some basidiomycetes are used as a source of medicinal compounds. Some are also used for "recreational" purposes. Some like rusts and smuts cause destruction of crop plants.

Deuteromyucetes

They are also called imperfect fungi because of their imperfect life-cycle, the sexual stage being undescribed. These fungi reproduce asexually,( i.e. by means of conidia) and are closely related to Ascomycetes, while a few are related to Basidiomycetes. Like higher fungi the mycelium is made up of branched, multinucleated, septate, interwoven hyphae. Some of the hyphae penetrate the substratum to absorb nourishment,. while some aerial hyphae are called conidiophores. The latter produce conidia which further give rise to mycelia.

Examples of imperfect fungi are Aspergillas and Helminthosporium.

Economic importance : The fungus Penicillium is used for the production of antibiotic penicillin. A few species are used to give flavor and texture to cheese. Some are also commercially used for the preparation of organic acid like citric acid, fumaric acid, oxalic acid, etc. Some members cause ring worm and athlete's foot. Some cause diseases in plants.

Ascomycetes and basidiomycetes are economically important fungi. Some of them are used in various industries while other are distinctly destructive. Yeast is used widely by brewers and bakers to prepare alcohol and in raising bread. It is also the main source of vitamin B and hormones like cytokinins. Some mushrooms are used as food for their delicacy and high nutritive value. Fungi like rusts and smuts cause destruction of crop plants while many other cause spoilage of milk, eggs, meat, fish, vegetables, fruit, etc.

3. Decomposers and parasitic forms

Decomposers

These serve as an important component of the ecosystem. They release hydrolytic enzymes into the substratum and break down the complex organic compound into simpler ones, release minerals and make them available to plants for recycling.

Examples: Rhizopus, Mucor, Agaricus, Penicillium, If it was not for the actions of decomposers, nutrients would get locked up in the dead matter of organisms. Life on earth without these organisms eventually would become impossible.

Role of decomposers

(1) They decompose the dead matter of plants and animals and disperse their nutrients, thus acting as scavangers of nature.

(2) They help in the formation of humus (superficial layer of soil rich in organic compounds) which is important to increase the fertility of soil and healthy growth of plants.

(3) They play an important role in converting complex organic components into simple forms to continue biogeochemical cycles.

Parasitic forms

These are pathogenic fungi. Unlike saprophytes or decomposers, they do not secrete hydrolytic enzymes, They live on or inside the body of the other living organisms (called hosts) obtain ready-made food from the latter and produce a number of diseases in them. Common plant diseases are potato blight, wheat rust, corn smut, and powdery mildew.

4. Lichens and mycorrhiza

Lichens

It is an obligatory association between an alga and a fungus, which together form a closely integrated unit.

The body of a lichen is composed of branching hyphae of a fungus, which harbor algal cells. The fungus gets food synthesized by the alga and the alga in return gets shelter, moisture and minerals absorbed by the fugal partner from the substrate.

Lichens are classified into three principle groups as follows:

1) Crustose lichens : These lichens form a hard granular crust closely adhering to rocks and tree trunks, e.g. Graphics.

(2) Foliose lichens : These lichens form leaf-like thalli with lobed margins attached to tree trunks, rocks, walls, etc. They are sometimes referred to as shelf fungus.
e.g. Parmelia.

(3) Fruticose lichens : These lichens form much branched shrub-like habit developing fruiting bodies, e.g. Usnea.

Economic importance of lichens : Lichens are used in varieties of ways. Some lichens are valuable source of food to wild animals like reindeer. Some lichens are fried and given to cattle as food and to some extent to human beings. Some are used in medicines and other are for preparation of dyes. Litmus is prepared from certain lichens and some are also used in the preparations of cosmetics and perfumes.

Ecological significance : Lichens growing on rocks disintegrate them to form soil, preparing the ground for mosses and subsequently for higher plants. Thus, they help in the succession of plant communities.

Kingdom Animalia

All animals are members of the Kingdom Animalia, also called Metazoa. This Kingdom does not contain the prokaryotes (Kingdom Monera, includes bacteria, blue-green algae) or the protists (Kingdom Protista, includes unicellular eukaryotic organisms). All members of the Animalia are multicellular, and all are heterotrophs (that is, they rely directly or indirectly on other organisms for their nourishment). Most ingest food and digest it in an internal cavity.

Animal cells lack the rigid cell walls that characterize plant cells. The bodies of most animals (all except sponges) are made up of cells organized into tissues, each tissue specialized to some degree to perform specific functions. In most, tissues are organized into even more specialized organs. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most reproduce sexually, by means of differentiated eggs and sperm. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. The development of most animals is characterized by distinctive stages, including a zygote, formed by the product of the first few division of cells following fertilization; a blastula, which is a hollow ball of cells formed by the developing zygote; and a gastrula, which is formed when the blastula folds in on itself to form a double-walled structure with an opening to the outside, the blastopore.

Somewhere around 9 or 10 million species of animals inhabit the earth; the exact number is not known and even our estimates are very rough. Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid. By far most species of animals are insects, with groups such as mollusks and nematodes also being especially diverse. By this measure our own group, the vertebrates, is relatively inconsequential.

Mesozoa

  • Phylum Mesozoa

Parazoa

Eumetazoa

  • Radiata
  • Bilateria
    • Protostomia
      • Acoelomates
      • Pseudocoelomates
        • Phylum Rotifera
        • Phylum Gastrotricha
        • Phylum Kinorhyncha
        • Phylum Gnathostomulida
        • Phylum Nematoda
        • Phylum Priapulida
        • Phylum Nematomorpha
        • Phylum Acanthocephala
        • Phylum Entoprocta
        • Phylum Loricifera
      • Eucoelomates
        • Phylum Mollusca
        • Phylum Annelida
        • Phylum Arthropoda
        • Phylum Echiurida
        • Phylum Sipuncula
        • Phylum Tardigrada
        • Phylum Pentastomida
        • Phylum Onychophora
        • Phylum Pogonophora
    • Deuterostomia
      • Phylum Phoronida
      • Phylum Ectoprocta
      • Phylum Brachiopoda
      • Phylum Echinodermata
      • Phylum Chaetognatha
      • Phylum Hemichordata
      • Phylum Chordata