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2. Biological Classification

Artificial Classification System:


This system was proposed by Linneaus. It was based on vegetative characters and androecium structure.
Natural Classification System: This system was used by George Bentham and Joseph Dalton Hooker. This system was based on natural affinities among organisms. In this system, both external and internal features were considered.

Two Kingdom Classification; as proposed by Linneaus:

  1. Animal Kingdom

  2. Plant Kingdom


Five Kingdom Classification; as proposed by R.H. Whittaker (1969):

This is the most accepted system of classification. The five kingdoms are as follows:

  1. Monera

  2. Protista

  3. Fungi

  4. Plantae and

  5. Animalia


The main criteria for classification used by Whittaker:

  1. Cell Structure

  2. Thallus Organization

  3. Mode of Nutrition

  4. Reproduction and

  5. Phylogenetic Relationships

KINGDOM MONERA

 

  1. The bacteria are kept under the Kingdom Monera. They are prokaryotic and possess cell wall. The cell wall is composed of polysaccharides and amino acids. Bacteria can be autotrophic and heterotrophic. The autotrophic bacteria can be chemosynthetic or photosynthetic. The heterotrophic bacteria can be saprophytic or parasitic.

  2. Based on their shape, bacteria are classified into four types:

  3. Spherical bacteria are called Coccus (pl.: cocci),

  4. Rod-shaped bacteria are called Bacillus (pl.: bacilli),

  5. Comma-shaped bacteria are called Vibrium (pl.: vibrio) and

Spiral shaped bacteria are called Spirillum (pl.: spirilla)

  1. Archaebacteria: The archaebacteria live in some of the harshest habitats. The different structure of their cell wall helps them in surviving in extreme conditions.
    Based on their habitats, the archaebacteria are classified as follows:
    Halophiles: They live in extremely salty areas.
    Thermoacidophiles: They live in hot spring.
    Methanogens: They live in marshy areas. They also live in the guts of the ruminant animals. They are responsible for the production of methane from the dung of these animals.

  2. Eubacteria: They are also called the ‘true bacteria’. They possess a rigid cell wall, and a flagellum (in motile bacteria). The cyanobacteria are also called ‘blue-green algae’ because they contain chlorophyll. The cyanobacteria can be unicellular or filamentous. They can live solitary or in colonies. The colony of cyanobacteria is usually surrounded by a gelatinous sheath. Some of the cyanobacteria are capable of nitrogen-fixation, e.g. Nostoc and Anabaena.

  3. Heterotrophic: These are the most abundant in nature. Most of them have economic significance for human beings. While many of them are beneficial for humans, many others are quite harmful.

Reproduction in Bacteria:


Binary fission is the usual mode of reproduction in bacteria. Under unfavourable conditions, they reproduce by spore formation. They also reproduce by adopting a primitive type of DNA transfer from one bacterium to another. This is similar to sexual reproduction.

KINGDOM PROTISTA

  1. They are eukaryotes and unicellular. Some of them have flagella or cilia for locomotion. Reproduction is asexual and sexual. Sexual reproduction is by a process of cell fusion and zygote formation.
    Kingdom Protista is divided into following groups:

Chrysophytes:

  1. The diatoms and golden algae (desmids) are included in this group. They are found in freshwater and marine habitats. They are microscopic and float passively in water currents and hence are considered as planktons. Organisms which cannot swim against the current are called planktons. Most of the chrysophytes are photosynthetic.
    The cell walls in diatoms form two thin overlapping shells; which fit together as the two parts of a soapbox. The cell walls are embedded with silica and hence are indestructible. Due to this, the diatoms leave behind a large amount of cell wall deposits in their habitat. The cell wall accumulation of diatoms; over billions of years is called ‘diatomaceous earth’. This soil is gritty and hence is used in polishing, filtration of oils and syrups. Diatoms are the main ‘producers’ in the oceans.

Dianoflagellates:

  1. They are usually marine and photosynthetic. Depending on the main pigments in their cells; they appear yellow, green, brown, blue or red. Stiff cellulose plates are present on the outer surface of cell wall in dianoflagellates. Two flagella are present in most of them. One flagellum lies longitudinally and another transversely in a furrow between the wall plates.

Euglenoids:

  1. Most of them live in freshwater habitat in stagnant water. Cell wall is absent in them and instead there is a protein rich layer; called pellicle. The pellicle makes their body flexible. Two flagella; one short and another long; are present. They are photosynthetic; but behave as heterotrophs in the absence of sunlight. Example: Euglena.

Slime Moulds:

  1. These are saprophytic. They body moves along decaying twigs and leaves and feeds on organic material. Under favourable conditions, they form an aggregation called plasmodium. The plasmodium may grow and spread over several feet. Under unfavourable conditions, the plasmodium differentiates and forms fruiting bodies. The fruiting bodies bear spores at their tips. True walls are present on the spores. The spores are extremely resistant and survive for many years. The spores are dispersed by air currents.

Protozoans:


They are heterotrophs and live as predators or parasites. The protozoans are classified into following four major groups:

  1. Amoeboid protozoans: The amoeboid protozoans live in freshwater, sea water or in moist soil. They produce pseudopodia for locomotion and for capturing food. The marine forms have silica shells on their surface. Some of them are parasites, e.g. Entamoeba histolytica.
     
    b. Flagellated protozoans: They are either free-living or parasitic. Flagella is present for locomotion. Many of them are parasites, e.g. Trypanosoma.
     
    c. Ciliated protozoans: They are aquatic. Cilia are present for locomotion. A cavity (gullet) is present which opens to the outside of the cell surface. The coordinated movement of cilia facilitates the entry of food-laden water into the gullet. Example: Paramoecium.
     
    d. Sporozoans: The sporozoans have an infectious spore-like stage in their life cycle. Example: Plasmodium.

KINGDOM FUNGI:

 

  1. The fungi are filamentous; except yeast (unicellular). The body consists of long, slender thread-like structures; called hyphae. The network of hyphae is called mycelium. Some hyphae are continuous tubes which are filled with multinucleated cytoplasm. Such hyphae are called coenocytic hyphae. The other type of hyphae has septae or cross-walls. The cell wall of fungi is composed of chitin and polysachharides.

  2. Most of the fungi are heterotrophic and are saprophytes. Some are parasites. Some of the fungi also live as symbionts. Some of the symbiont fungi live as lichens; in association with algae. Some of the symbiont fungi live as mycorrhiza; in association with roots of higher plants.

Reproduction in Fungi:

 

  1. Reproduction by vegetative means takes place by fragmentation, fission and budding. Some fungi reproduce asexually by forming spores which are called conidia or sporangiospores or zoospores. Sexual reproduction is by oospores, ascospores and basidiospores. The spores are produced in distinct structures called fruiting bodies.

  2. The sexual cycle involves three steps which are as follows:
    Plasmogamy: This involves fusion of protoplasm between two motile or non-motile gametes.
    Karyogamy: This involves fusion of two nuclei.
    Formation of haploid spores: This happens because of meiosis in zygote.
    During sexual reproduction, two haploid hyphae of compatible mating types come together and fuse. In some fungi, the fusion of two haploid cells immediately results in a diploid cell (2n). In other fungi (ascomycetes and basidiomycetes), an intervening dikaryotic stage occurs. In this stage, two nuclei are present in each cell. This condition is called dikayron. The parental nuclei fuse at a later stage and the cells become diploid. Reduction division in the fruiting bodies leads to the formation of haploid spores.
    On the basis of morphology of mycelium, mode of spore formation and fruiting bodies; Kingdom Fungi is divided into following classes:

Phycomycetes:

 

  1. The members of phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places. They can also be found as obligate parasites on plants.

  2. Mycelium: Aseptate and coenocytic.

Reproduction:

  1. Asexual reproduction is by zoospores (motile) or by aplanospores (non-motile). These spores are endogeneously produced in sporangium.
    Zygospores are formed by fusion of two gametes. The gametes can be similar (isogamous) or dissimilar (anisogamous).
    Examples: Mucor, Rhizopus and Albugo (the parasitic fungi on mustard).

Ascomycetes:

  1. They are commonly known as sac-fungi. They are unicellular or multicellular. They are saprophytic, decomposers, parasitic or coprophilous. Those growing on dung are called coprophilous.

  2. Mycelium: Branched and septate.

Reproduction:

  1. Asexual spores are exogenously produced on the special mycelium called conidiophores. Sexual spores are called ascospores. They are produced endogenously in sac like asci. These asci are arranged in various kinds of fruiting bodies called ascocarps.

  2. Examples: Aspergillus, Claviceps, Neurospora, yeast, penicillium, morels, baffles, etc.

Basidiomycetes:

  1. They grow in soil, on logs and tree stumps. Some of them also grow in living plant bodies as parasites. Mushrooms, bracket fungi or puffballs are the commonly known forms.

  2. Mycelium: Branched and septate.

Reproduction:

  1. Asexual spores are usually absent. Vegetative reproduction by fragmentation is common. Sex organs are absent. But plasmogamy is brought about by fusion of two vegetative cells of different strains. The resultant structure is dikaryotic which finally forms the basidium. Karyogamy and meiosis are responsible for formation of four basidiospores in a basidium. The basiodiospores are exogenously produced. Basidia are arranged in fruiting bodies called basidiocarps.
    Examples: Agaricus (mushroom), Ustilago (smut) and Puccinia (rust).

Deuteromycetes:

 

  1. They are usually known as imperfect fungi because only the asexual or vegetative phase of them is known. A large number of deuteromycetes are decomposers, while some members are parasites.

  2. Mycelium: Branched and septate.

  3. Examples: Alternaria, Colletotrichum and Trichoderma.

KINGDOM PLANTAE

  1. All eukaryotes which have chloroplast are kept under this kingdom. Most of them are autotrophic; but some are heterotrophic. Cell wall is mainly composed of cellulose.

  2. The life cycle of plants has two distinct phases; the diploid saprophytic and the haploid gametophytic phase. These phases alternate with each other. The lengths of the haploid and diploid phases vary among different groups of plants. This phenomenon is called Alternation of Generation.

KINGDOM ANIMALIA

 

  1. All multicellular eukaryotes which lack cell wall and are heterotrophs are kept under this kingdom. The animals indirectly or directly depend for food on plants. They follow the holozoic mode of nutrition. Holozoic nutrition involves ingestion of food and use of internal cavity for digestion of food. Most of the animals are capable of locomotion. Sexual reproduction is by copulation of male and female which is followed by embryological development.

VIRUSES, VIROIDS AND LICHENS:

  1. Virus is non-cellular organism. It is characterized by an inert crystalline structure outside the living cell. Once a virus infects a living cell, it begins to replicate and kills the host in the process. Virus is considered as a borderline case between living and non-living.
    The name virus was given by Pasteur D. J. Ivanowsky (1892). M. W. Beijerinek (1898) demonstrated that the extract of infected tobacco plants could cause infection in healthy plants. He called the fluid from the infected plant as Contagium vivum fluidum (infectious living fluid). W. M. Stanley (1935) demonstrated that viruses could be crystallized and the crystals mainly consist of proteins.

    Viruses also contain genetic material; which can be either RNA or DNA. Both RNA and DNA cannot be present in the same virus. Plant infecting viruses usually have single-stranded RNA and animal infecting viruses usually have double-stranded RNA or double-stranded DNA. Bacteriophages (bacterial viruses) usually have double-stranded DNA.

    The protein coat on the virus is called capsid. It is made up of small subunits called capsomeres. The capsid protects the nucleic acid. The capsomeres are arranged in helical or polyhedral geometric forms.
    Mumps, small pox, herpes, influenza and AIDS are examples of viral diseases in humans. In plants; viral infection leads to the symptoms; like mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.
     

REVISION NOTES

 

CLASS 11 BIOLOGY

UNIT I – DIVERSITY IN THE LIVING WORLD

Chapter 1 – The Living World 

Chapter 2 – Biological Classification 

Chapter 3 – Plant Kingdom 

Chapter 4 – Animal Kingdom 

UNIT II – STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS

Chapter 5 – Morphology of Flowering Plants 

Chapter 6 – Anatomy of Flowering Plants 

Chapter 7 – Structural Organisation in Animals 

UNIT III – CELL : STRUCTURE AND FUNCTIONS

 

Chapter 8 – Cell: The Unit of Life 

Chapter 9 – Bio-Molecules 

Chapter 10 – Cell Cycle and Cell Division 

UNIT IV – PLANT PHYSIOLOGY 

Chapter 11 – Transport in Plants 

Chapter 12 – Mineral Nutrition 

Chapter 13 – Photosynthesis in higher plants 

Chapter 14 – Respiration in Plants 

Chapter 15 – Plant Growth and Development 

UNIT V – HUMAN PHYSIOLOGY 

Chapter 16 – Digestion And Absorption 

Chapter 17 – Breathing and Exchange of Gases 

Chapter 18 – Body fluids and circulation 

Chapter 19 – Excretory Products and their Elimination 

Chapter 20 – Locomotion and Movement 

Chapter 21 – Neural Control and Coordination 

Chapter 22 – Chemical Coordination and Integration 

CLASS 12 BIOLOGY

Unit-VI Reproduction
  

Chapter 1 : Reproduction in Organisms 

Chapter 2 : Sexual Reproduction in Flowering Plants 

Chapter 3 : Human Reproduction 

Chapter 4 : Reproductive Health 

Unit-VII Genetics and Evolution

Chapter 5 : Principles of Inheritance and Variation 

Chapter 6 : Molecular Basis of Inheritance 

Chapter 7 : Evolution 

Unit-VIII Biology and Human Welfare

Chapter 8 : Human Health and Disease 

Chapter 9 : Strategies for Enhancement in Food Production 

Chapter 10 : Microbes in Human Welfare 

Unit-IX Biotechnology  

Chapter 11 : Biotechnology Principles and Processes 

Chapter 12 : Biotechnology and its Applications 

Unit-X Ecology and Environment 

Chapter 13 : Organisms and Populations 

Chapter 14 : Ecosystem 

Chapter 15 : Biodiversity and Conservation 

Chapter 16 : Environmental Issues 

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