NCERT class 11th (Hindi)

NCERT TEXT BOOK

Biology

class 11th (Hindi)

CONTENT PAGE

UNIT I – DIVERSITY IN THE LIVING WORL

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 : Biomolecules

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

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CHAPTER 9 – BIOMOLECULES

BIOMOLECULES

  • All living organisms are made up of similar elements
  • In living organisms Carbon and Hydrogen are in abundance with respect to other elements.           

            How to Analyse Chemical Composition?

  • To analyze the chemical composition, We can take any living tissue and grind it in trichloroacetic acid (Cl3CCOOH) using a mortar and a pestle. We obtain a thick slurry. If we were to strain this through a cheesecloth or cotton we would obtain two fractions
  1. filtrate or the acid-soluble pool,
  2. retentate or the acid-insoluble fraction.
  • Scientists have found thousands of organic compounds in the acid-soluble pool.
  • All the carbon compounds that we get from living tissues can be called ‘biomolecules’.

Living organisms have also got inorganic elements and compounds in them.

  • Wet weight – weight of living tissue/structure.
  • Dry Weight – weight of structure after drying it. (Wet weight – water).
  • Ash – ifthe tissue is fully burnt, all the carbon compounds are oxidised to gaseous form (CO2, water vapour) and are removed. What is remaining is called ‘ash’. This ash contains inorganic elements (like calcium, magnesium etc). (Dry weight – carbon compound)

Table : A Comparison of Elements Present in Non-living and Living Matter

Element % Weight of
Earth’s crust Human body
Hydrogen (H) 0.14 0.5
Carbon   (C) 0.03 18.5
Oxygen (O) 46.6 65.0
Nitrogen (N) very little 3.3
Sulphur (S) 0.03 0.3
Sodium (Na) 2.8 0.2
Calcium (Ca) 3.6 1.5
Magnesium (Mg) 2.1 0.1
Silicon (Si) 27.7 negligible

 

Table : A List of Representative Inorganic Constituents of Living Tissues

Component Formula
Sodium Na+
Potassium K+
Calcium Ca+2
Magnesium Mg+2
Water H2O
Compounds NaCl, CaCO3, PO4–3, SO4–2

Amino acids

  • Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon i.e., the α-carbon. Hence, they are called α-amino acids. They are substituted methanes.
  • There are four substituent groups occupying the four valency positions. These are hydrogen, carboxyl group, amino group and a variable group designated as R group.
  • Based on the nature of R group there are many amino acids. However, those which occur in proteins are only of twentyone types.
    • R group = hydrogen e.g., glycine
    • R group = methyl group e.g., alanine
    • R group = hydroxy methyl e.g., serine.

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  • The chemical and physical properties of amino acids are essentially of the amino, carboxyl and the R functional groups.
    • Acidic amino acid – glutamic acid etc.
    • Basic amino acid – lysine
    • Neutral amino acid – valine.
    • aromatic amino acids – tyrosine, phenylalanine, tryptophan.
  • A particular property of amino acids is the ionizable nature of-NH2 and -COOH groups. Hence in solutions of different pHs, the structure of amino acids changes.

 

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Lipids

  • Lipids are generally water insoluble. They could be simple fatty acids.
  • A fatty acid has a carboxyl group attached to an R group. The R group could be a methyl (-CH3), or ethyl (-C2H5) or higher number of-CH2 groups (1 carbon to 19 carbons).
    • Palmitic acid has 16 carbons including carboxyl carbon.
    • Arachidonic acid has 20 carbon atoms including the carboxyl carbon.
  • Fatty acids could be saturated (without double bond) or unsaturated (with one or more C=C double bonds).
  • Another simple lipid is glycerol which is trihydroxy propane.
  • Many lipids have both glycerol and fatty acids. Here the fatty acids are found esterified with glycerol. They can be then monoglycerides, diglycerides and triglycerides.
  • These are also called fats and oils based on melting point. Oils have lower melting point (e.g., gingely oil) and hence remain as oil in winters.
  • Some lipids have phosphorous and a phosphorylated organic compound in them. These are phospholipids. They are found in cell membrane. Lecithin is one example.
  • Some tissues especially the neural tissues have lipids with more complex structures.

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Nucleotides

  • Many carbon compounds have heterocyclic rings like nitrogen bases -adenine, guanine, cytosine, uracil, and thymine.
  • When found attached to a sugar, they are called nucleosides.(nucleoside = sugar + nitrogen base). Adenosine, guanosine, thymidine, uridine and cytidine are nucleosides.
  • If a phosphate group is also found esterified to the sugar they are called nucleotides. (Nucleotides = nucleosides + phosphate). Adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid are nucleotides.
  • Nucleic acids like DNA and RNA consist of nucleotides only. DNA and RNA function as genetic material.

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Primary and Secondary Metabolites

  • Primary metabolites – Biomolecules which are present in all organisms and have identifiable functions and play known roles in normal physiologial processes.
  • Secondary metabolites – In plants, fungus and microbes many compounds other than primary metabolites are present. e.g,alkaloides, flavonoides, rubber, essential oils, antibiotics,coloured pigments, scents, gums, spices. The role or functions of all the secondary metabolitesare not known yet. many of them are useful to ‘human welfare’ (e.g., rubber, drugs, spices, scents and pigments). Some secondary metabolites have ecological importance.

 

Table : Some Secondary Metabolites
Pigments Carotenoids, Anthocyanins, etc.
Alkaloids Morphine, Codeine, etc.
Terpenoides Monoterpenes, Diterpenes etc.
Essential oils Lemon grass oil, etc.
Toxins Abrin, Ricin
Lectins Concanavalin A
Drugs Vinblastin, curcumin, etc.
Polymeric substances Rubber, gums, cellulose

BIOMACROMOLECULES

  • There is one feature common to all those compounds found in the acid soluble pool. They have molecular weights ranging from 18 to around 800 daltons (Da) approximately. (Micromolecules) (Mw= <1000 daltons)
  • The acid insoluble fraction, has only four types of organic compounds i.e., proteins, nucleic acids, polysaccharides and lipids. These classes of compounds with the exception of lipids, have molecular weights in the range of ten thousand daltons and above. (Macromolecules) (Mw= >1000 daltons)
  • The molecules in the insoluble fraction with the exception of lipids are polymeric substances.
  • Lipids are small molecular weightcompounds and are present not only as such but also arranged into structures like cell membrane and other membranes. When we grind a tissue, we are disrupting the cell structure. Cell membrane and other membranes are broken into pieces, and form vesicles which are not water soluble. Therefore, these membrane fragments in the form of vesicles get separated along with the acid insoluble pool and hence in the macromolecular fraction. Lipids are not strictly macromolecules.
  • The acid soluble pool represents roughly the cytoplasmic composition. The macromolecules from cytoplasm and organelles become the acid insoluble fraction. Together they represent the entire chemical composition of living tissues or organisms.

Table : Average Composition of Cells

Component % of the total cellular mass
Water 70-90
Proteins 10-15
Carbohydrates 3
Lipids 2
Nucleic acids 5-7
Ions 1

 

PROTEINS

  • Proteins are polypeptides. They are linear chains of amino acids linked by peptide bonds.
  • Each protein is a polymer of amino acids. As there are 21 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.), a protein is a heteropolymer and not a homopolymer.
  • A homopolymer has only one type of monomer repeating ‘n’ number of times.
  • Amino acids can be essential or non-essential. Essential amino acids are supplied in diet while our body prepares non essential amino acids.
  • Proteins carry out many functions in living organisms, some transport nutrients across cell membrane, some fight infectious organisms, some are hormones, some are enzymes,etc.
  • Collagen is the most abundant protein in animal world.
  • Ribulose bisphosphate Carboxylase-Oxygenase (RUBISCO) is the most abundant protein in the whole of the biosphere.

Table : Some Proteins and their Functions

Protein Functions
Collagen Intercellular ground substance
Trypsin Enzyme
Insulin Hormone
Antibody Fights infectious agents
Receptor Sensory reception (smell, taste, hormone, etc.)
GLUT-4 Enables glucose transport into cells

 

POLYSACCHARIDES

  • Polysaccharides are long chains of sugars. They are threads (literally a cotton thread) containing different monosaccharides as building blocks.

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  • Celluloseis a polymeric polysaccharide consisting of only one type of monosaccharide i.e., glucose. Cellulose is a homopolymer.
  • Starch is a variant of this but present as a store house of energy in plant tissues. Animals have another variant called glycogen.
  • Inulin is a polymer of fructose.
  • In a polysaccharide chain (say glycogen), the right end is called the reducing end and the left end is called the non-reducing end. It has branches.
  • Starch forms helical secondary structures. In fact, starch can hold I2 molecules in the helical portion. The starch-I2 is blue in colour. Cellulose does not contain complex helices and hence cannot hold I2.
  • Plant cell walls are made of cellulose. Paper made from plant pulp is cellulose. Cotton fibre is cellulose.
  • There are more complex polysaccharides in nature. They act as building blocks, amino-sugars and chemically modified sugars (e.g., glucosamine, N-acetyl galactosamine, etc.).
  • Exoskeletons of arthropods, for example, have a complex polysaccharide called chitin. These complex polysaccharides are heteropolymers.

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NUCLEIC ACIDS

  • Present in acid insoluble fraction of all living tissues.
  • These are polynucleotides. For nucleic acids, the building block is a nucleotide. A nucleotide has three chemically distinct components. One is a heterocyclic compound (N2 bases, the second is a monosaccharide and the third a phosphoric acid or phosphate.)
  • Adenine, Guanine, Uracil, Cytosine, and Thymine are N2 containing bases. Adenine and Guanine are substituted purines while the rest are substituted pyrimidines.
  • The sugar found in polynucleotides is either ribose (a monosaccharide pentose) or 2′ deoxyribose.
  • A nucleic acid containing deoxyribose is called deoxyribonucleic acid (DNA) while that which contains ribose is called ribonucleic acid (RNA).

STRUCTURE OF PROTEINS

  • Proteins are heteropolymers containing strings of amino acids. \
  • Biologists describe the protein structure at four levels.
    • Primary structure –

It is linear structure of protein.

the left end represented by the first amino acid and the right end represented by the last amino acid.

The first aminoacid is also called as N-terminal amino acid. The last amino acid is called the C-terminal amino acid.

Secondary structure –

The linear protein thread is folded in the form of a helix (similar to a revolving staircase).In proteins, only right handed helices are observed.

Tertiary structure –

The long protein chain is also folded upon itself like a hollow wollen ball, giving rise to the tertiary structure. This gives us a 3-dimensional view of a protein. Tertiary structure is absolutely necessary for the many biological activities of proteins.

Quaternary structure –

Some proteins are an assembly of more than one polypeptide or subunits. The manner in which these individual folded polypeptides or subunits are arranged with respect to each other (e.g. linear string of spheres, spheres arranged one upon each other in the form of a cube or plate etc.) is the architecture of a protein otherwise called the quaternary structure of a protein.

e.g., Adulthuman haemoglobin consists of 4 subunits. Two of these are identical to each other. Hence, two subunits of α type and two subunits of β type together constitute the human haemoglobin (Hb).

 

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NATURE OF BOND LINKING MONOMERS IN A POLYMER

  • In a polypeptide or a protein, amino acids are linked by a peptide bond which is formed when the carboxyl (-COOH) group of one amino acid reacts with the amino (-NH2) group of the next amino acid with the elimination of a water moiety (the process is called dehydration).
  • In a polysaccharide the individual monosaccharides are linked by a glycosidic bond. This bond is also formed by dehydration. This bond is formed between two carbon atoms of two adjacent monosaccharides.
  • In a nucleicacid a phosphate moiety links the 3′-carbon of one sugar of one nucleotide to the 5′-carbon of the sugar of the succeeding nucleotide. The bond between the phosphate and hydroxyl group of sugar is an ester As there is one such ester bond on either side, it is called phosphodiester bond.

Nucleic acids exhibit a wide variety of secondary structures.

one of the secondary structures exhibited by DNA is the famous Watson-Crick model.

Watson-Crick Model

  • According to this model DNA exists as a double helix. The two strands of polynucleotides are antiparallel i.e., run in the opposite direction.
  • The backbone is formed by the sugar-phosphate-sugar chain.
  • The nitrogen bases are projected more or less perpendicular to this backbone but face inside.
  • A and G of one strand compulsorily base pairswith T and C, respectively, on the other strand. There are two hydrogen bonds between A and T. There are three hydrogen bonds between G and C.
  • Each strand appears like a helical staircase.
  • Each step of ascent is represented by a pair of bases. At each step of ascent, the strand turns 36°.
  • One full turn of the helical strand would involve ten steps or ten base pairs.
  • On drawing a line diagram, the pitch would be 34Å. The rise per base pair would be 3.4Å. This form of DNA with the above mentioned salient features is called B-DNA.
  • There are more than a dozen forms of DNA named after English alphabets with unique structural features.

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DYNAMIC STATE OF BODY CONSTITUENTS – CONCEPT OF METABOLISM

  • living organisms contain thousands of organic compounds. These compounds or biomolecules are present in certain concentrations (expressed as mols/cell or mols/litre etc.).
  • allthese biomolecules have a turn over. This means that they are constantly being changed into some other biomolecules and also made from some other biomoleculesthrough chemical reactions. Together all these chemical reactions are called
  • These metabolic reactions result in the transformation of biomolecules like removal of CO2 from amino acids making an amino acid into an amine, removal of amino group in a nucleotide base; hydrolysis of a glycosidic bond in a disaccharide, etc.
  • Majority of these metabolic reactions are always linked to some other reactions or the metabolites are converted into each other in a series of linked reactions called metabolic pathways.
  • Flow of metabolites through metabolic pathway has a definite rate and direction. This metabolite flow is called the dynamic state of body constituents.
  • Another feature of these metabolic reactions is that every chemical reaction is a catalysed reaction. There is no uncatalysed metabolic conversion in living systems.
  • The catalysts which hasten the rate of a given metabolic conversation are also proteins. These proteins with catalytic power are named

METABOLIC BASIS FOR LIVING

  • Metabolic pathways can lead to a more complex structure from a simpler structure (for example, acetic acid becomes cholesterol) =anabolic pathways,or lead to a simpler structure from a complex structure (for example, glucose becomes lactic acid in our skeletal muscle)=catabolic pathways.
  • Anabolic pathways, as expected, consume energy. While, catabolic pathways lead to the release of energy, which is stored in the form of chemical bonds in ATP(adenosine triphosphate).

THE LIVING STATE

  • Many chemical compounds or metabolites, or biomolecules, are present at concentrations characteristic of each of them.

e.g., the blood concentration of glucose in a normal healthy individual is 4.5-5.0 mM, while that of hormones would be nanograms/ mL.

  • all living organisms exist in a steady-state characterised by concentrations of each of these biomolecules. These biomolecules are in a metabolic flux. Any chemical or physical process moves spontaneously to equilibrium.
  • The steady state is a non-equilibirium state. Because systems at equilibrium cannot perform work.
  • the living state is a non-equilibrium steady-state to be able to perform work; living process is a constant effort to prevent falling into equilibrium. This is achieved by energy input. Metabolism provides a mechanism for the production of energy. Hence the living state and metabolism are synonymous. Without metabolism there cannot be a living state.

 

ENZYMES

  • Almost all enzymes are proteins. There are some nucleic acids that behave like enzymes. These are called ribozymes.
  • An enzyme like any protein has a primary structure,secondary and the tertiary structure.
  • In tertiary structure, the backbone of the protein chain folds upon itself, the chain criss-crosses itself and hence, many crevices or pockets are made. One such pocket is the ‘active site’.
  • An active site of an enzyme is a crevice or pocket into which the substrate fits. Thus enzymes, through their active site, catalyse reactions at a high rate.
  • Enzyme catalysts differ from inorganic catalysts in many ways. Inorganic catalysts work efficiently at high temperatures and high pressures, while enzymes get damaged at high temperatures (above 40°C).

However, enzymes isolated from organisms who normally live under extremely high temperatures (e.g., hot vents and sulphur springs), are stable and retain their catalytic power even at high temperatures (upto 80°-90°C). Thermal stability is thus an important quality of such enzymes isolated from thermophilic organisms.

Chemical Reactions

  • Chemical compounds undergo two types of changes.

A physical change simply refers to a change in shape without breaking of bonds. This is a physical process. Another physical process is a change in state of matter: when ice melts into water, or when water becomes a vapour.

when bonds are broken and new bonds are formed during transformation, this will be called a chemical reaction. For example:

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hydrolysis of starch into glucose is an organic chemical reaction.

  • Rate of a physical or chemical process refers to the amount of product formed per unit time. It can be expressed as:

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Rate can also be called velocity if the direction is specified.

  • Rates of physical and chemical processes are influenced by temperature among other factors.
  • A general rule is that rate doubles or decreases by half for every 10°C change in either direction. Catalysed reactions proceed at rates vastly higher than that of uncatalysed ones. e.g.,

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In the absence of any enzyme this reaction is very slow, with about 200 molecules of H2CO3 being formed in an hour. However, by using the enzyme carbonic anhydrase, the reaction speeds about 600,000 molecules being formed every second.

  • A multistep chemical reaction, when each of the steps is catalysed by the same enzyme complex or different enzymes, is called a metabolic pathway. For example,

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This reaction is actually a metabolic pathway in which glucose becomes pyruvic acid through ten different enzyme catalysed metabolic reactions.

  • This pathway provides different products in different conditions –

In our skeletal muscle, under anaerobic conditions, lactic acid is formed.

Under normal aerobic conditions, pyruvic acid is formed.

In yeast, during fermentation, the same pathway leads to the production of ethanol (alcohol).

 How do Enzymes bring about such High Rates of Chemical Conversions?

  • Enzymes, i.e. proteins with three dimensional structures including an ‘active site’, convert a substrate (S) into a product (P). Symbolically, this can be depicted as:

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  • Substrate ‘S’ has to bind the enzyme at its ‘active site’ within a given cleft or pocket. The substrate has to diffusetowards the ‘active site’.
  • There is thus, an obligatory formation of an ‘ES’ complex. E stands for enzyme. This complex formation is a transient phenomenon.
  • During the state where substrate is bound to the enzyme active site, a new structure of the substrate called transition state structure is formed.
  • Very soon, after the expected bond breaking/making is completed, the product is released from the active site. In other words, the structure of substrate gets transformed into the structure of product(s).
  • There could be many more ‘altered structural states’ between the stable substrate and the product. all otherintermediate structural states are unstable. Stability is something related to energy status of the molecule or the structure.
  • If ‘P’ is at a lower level than’S’, the reaction is an exothermic reaction. One need not supply energy (by heating) in order to form the product.
  • However, whether it is an exothermic or spontaneous reaction or an endothermic or energy requiring reaction, the ‘S’ has to go through a much higher energy state or transition state.
  • The difference in average energy content of’S’ from that of this transition state is called ‘activation energy’.
  • Enzymes eventually bring down this energy barrier making the transition of’S’ to ‘P’ more easy.

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     Nature of Enzyme Action

  • Each enzyme (E) has a substrate (S) binding site in its molecule so that a highly reactive enzyme-substrate complex (ES) is produced. This complex is short-lived and dissociates into its product(s) P and the unchanged enzyme with an intermediate formation of the enzyme-product complex (EP).

The formation of the ES complex is essential for catalysis.

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  • The catalytic cycle of an enzyme action can be described in the following steps:
  1. First, the substrate binds to the active site of the enzyme, fitting into the active site.
  2. The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate.
  3. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new enzyme- product complex is formed.
  4. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again.

Factors Affecting Enzyme Activity

Factors affecting Enzyme activity are temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity.

  1. Temperature and pH

Enzymes generally function in a narrow range of temperature and pH.

Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH.

Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat.

  1. Concentration of Substrate

With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first. The reaction ultimately reaches a maximum velocity (Vmax) which is not exceeded by any further rise in concentration of the substrate. This is because the enzyme molecules are fewer than the substrate molecules and after saturation of these molecules, there are no free enzyme molecules to bind with the additional substrate molecules.

The activity of an enzyme is also sensitive to the presence of specific chemicals that bind to the enzyme. When the binding of the chemical shuts off enzyme activity, the process is called inhibition and the chemical is called an inhibitor.

Competitive inhibition –

When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. Due to its close structural similarity with the substrate, the inhibitor competes with the substrate for the substrate-binding site of the enzyme. Consequently, the substrate cannot bind and as a result, the enzyme action declines,

e.g., inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure.

Such competitive inhibitors are often used in the control of bacterial pathogens.

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Classification and Nomenclature of Enzymes

Enzymes are divided into 6 classes each with 4-13 subclasses and named accordingly by a four-digit number.

  1. Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates S and S’ e.g.,
  2. Transferases: Enzymes catalysing a transfer of a group, G (other than hydrogen) between a pair of substrate S and S’ e.g.,
  3. Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
  4. Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.
  5. Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.
  6. Ligases: Enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds.

   Co-factors        

  • Enzymes are composed of one or several polypeptide chains. However, there are a number of cases in which non-protein constituents called co-factors are bound to the enzyme to make the enzyme catalytically active.
  • In these instances, the protein portion of the enzymes is called the apoenzyme.
  • Three kinds of cofactors may be identified: prosthetic groups, co-enzymes and metal ions.
  • Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are tightly bound to the apoenzyme.

For example, in peroxidase and catalase, which catalyze the breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is a part of the active site of the enzyme.

  • Co-enzymes are also organic compounds but their association with the apoenzyme is only transient, usually occurring during the course of catalysis. Furthermore, co-enzymes serve as co-factors in a number of different enzyme catalyzed reactions. The essential chemical components of many coenzymes are vitamins, e.g., coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin.
  • Metal ions – A number of enzymes require metal ions for their activity which form coordination bonds with side chains at the active site and at the same time form one or more cordination bonds with the substrate, e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase.

Catalytic activity is lost when the co-factor is removed from the enzyme which testifies that they play a crucial role in the catalytic activity of the enzyme.

 

 

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CHAPTER 9 ncert

 

CH 8 – CELL: THE UNIT OF LIFE

CELL: THE UNIT OF LIFE

  • Cell   is —  Basic unit of life

—  Fundamental structural and functional unit of all living organisms.

  • Cytology – study of cell and cellular structures.
  • Types of organisms –

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  • All unicellular organisms are capable of
    • Independent existence.
    • Performing the essential functions of life.

Anything less than a complete structure of a cell does not ensure independent living. Hence, cell is the fundamental structural and functional unit of all living organisms.

  • Some important scientists –
Name of scientist Their work
Robert hooke Discovered cell
Anton von Leeuwenhoek first saw and described a live cell
Robert Brown Discovered nucleus
Schleiden (German botanist), Schwann (British Zoologist) Formulated Cell Theory
  • Robert hooke first time describe about cell in his book ‘Micrographia’. He actually saw cell wall of dead cells not cell itself.

 

  • CELL THEORY

    • Formulated by Schleiden and Schwann.
    • Modified by Rudolf Virchow – he explained that new cells develop from pre existing cells by cell division (Omnis cellula-e cellula).
    • Exception of cell theory – virus, viriods,
  1. All living organisms are composed of cells and products of cells.
  2. Cell is structural unit of life.
  • All cells arise from pre-existing cells.

 

  • CELL SIZE AND SHAPE

    • Smallest cell – mycoplasmas (PPLO – Pleuro Pneumonia Like Organisms)
    • Largest cell – egg of an ostrich.
    • Smallest cell in human body – Red Blood Cell.
    • Largest cell in human body – Ovum.
    • Longest cell in human body – Nerve Cell.

Even shape of cells may vary with the functions they perform.

 

  • TYPES OF CELL

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PROKARYOTIC CELL

  • Represented by Blue Green Algae, mycoplasmas, bacteria etc.

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  • Cell wall
    • Determine shape of cell.
    • Provide strong, structural support
    • Prevent bacteria from bursting or collapsing

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  • Plasma membrane
    • Semipermeable
    • Structurally similar to that of eukaryotes.
  • Mesosomes
    • Formed by extension of plasma membrane into cell.
    • In the form of vesicles, tubules and lamella.
    • Help in cell wall formation, DNA replication and distribution to daughter cells.
    • Also help in respiration, secretion processes, to increase the surface area of the plasma membrane and enzymatic content.
  • Chromatophores
    • Membranous extensions into cytoplasm.
    • Contain pigments.
    • In cyanobacteria.
  • Flagella
    • Present in motile cells.
    • Thin filamentous extensions from their cell wall.
    • Composed of three parts – filament, hook and basal body.
  • Pili and Fimbriae
    • Pili are elongated tubular structure while fimbriae are small bristle like fibres.
    • Help in attachment of bacteria.
  • Ribosomes
    • Associated with the plasma membrane of the cell.
    • Made of two subunits – 50S and 30S units which when present together form 70S.

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  • Site of protein synthesis.
  • Ribosome of a polysome translate the mRNA into protein.

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  • Inclusion bodies
    • For storage of reserve material in prokaryotic cells.
    • These are not bounded by any membrane system and lie free in the cytoplasm.
    • g., phosphate granules, cyanophycean granules and glycogen granules.
    • Gas vacuoles are found in blue green and purple and green photosynthetic bacteria.

 

EUKARYOTIC CELLS

  • Include all the protists, plants, animals and fungi.
  • Extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles present.
  • possess an organised nucleus with a nuclear envelope.
  • genetic material is organised into chromosomes.

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  • Cell wall
    • non-living, rigid structure
    • forms an outer covering for the plasma membrane of fungi and plants.
    • gives shape to the cell and protects the cell from mechanical damage and infection.
    • it also helps in cell-to-cell interaction and provides barrier to undesirable macromolecules.

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  • Layers of cell wall
  1. Middle lamella
  • Outermost
  • Made up of mainly calcium pectate.
  • Holds or glues the different neighbouring cell together.
  1. Primary wall
    • Capable of growth.
    • Present in young cell.
    • Gradually diminishes as cell matures.
    • Madeup of cellulose, hemicelluloses.
    • Present in meristem, pith, cortex etc.
  2. Secondary wall
    • Innermost layer.
    • Lignified (in sclerenchyma, vesels, tracheids), suberinised (casparian strips, endodermis)
    • Suberin, lignin make cell wall impermeable.
    • Present in sclerenchyma, collenchyma, and vessels, tracheids.

 

  • Cell wall and middle lamella maybe traversed by plasmodesmata which connects the cytoplasm of neighbouring cells.

 

  • Cell membrane
    • Mainly composed of bilayer phospholipids, also possess protein and carbohydrate.
    • lipids are arranged within the membrane with the polar head (hydrophilic) towards the outer sides and the nonpolar tails (hydrophobic) towards the inner part.

This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment.

  • The ratio of protein and lipid varies in different cell types.

( In human RBC membrane has 52% protein and 40% lipids.)

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  • Structure of cell membrane is explained by Fluid Mosaic Model which was given by Singer and Nicolsan.
  • According to this model the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer.
  • The fluid nature of the membrane is important for functions like cell growth, formation of intercellular junctions, secretion, endocytosis, cell division etc.

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Fluid Mosaic Model

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  • Mitochondria
    • Double membrane bound cell organelle.

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  • Mitochondria are site of aerobic respiration. They produce ATP, hence called ‘Power House Of Cell’.
  • The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins. So, mitochondria also known as ‘semi autonomous organelle’.
  • The mitochondria divide by fission and produce new mitochondria.

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  • Plastids
    • Found in all plant cells and in euglenoides.
    • They bear some specific pigments, thus imparting specific colours to the plants.

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  • Chloroplasts are mainly found in the mesophyll cells of the leaves.
  • These are various shaped like lens, oval, spherical, discoid, ribbon.
  • Double membrane bound Cell organelle. Inner is less permeable than outer.

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  • There are also stroma lamellae connecting the thylakoids of the different grana.
  • Stroma also contains small, double-stranded circular DNA molecules and ribosomes (70S). so, it is also known ‘semi autonomous organelle’.

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  • Endoplasmic Reticulum
    • a network or reticulum of tiny tubular structures scattered in the cytoplasm that is called the endoplasmic reticulum (ER)
    • Hence, ER divides the intracellular space into two distinct compartments, i.e., luminal(inside ER) and extra luminal(cytoplasm).

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  • Golgi apparatus
    • Discovered by Camillo Golgi.
    • They consist of many flat, disc-shaped sacs or cisternae stacked parallely.
    • The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis or the forming face and concave trans or the maturing face, which are interconnected.
    • The golgi apparatus principally performs the function of packaging materials.
    • golgi apparatus remains in close association with the endoplasmic reticulum as materials to be packaged in the form of vesicles from the ER fuse with the cis face of the golgi apparatus and move towards the maturing face.
    • A number of proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the cisternae of the golgi apparatus before they are released from its trans
    • Golgi apparatus is the important site of formation of glycoproteins and glycolipids

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  • Lysosomes
    • These are membrane bound vesicular structures formed by the process of packaging in the golgi apparatus.
    • The isolated lysosomal vesicles have been found to be very rich in almost all types of hydrolytic enzymes (hydrolases – lipases, proteases, carbohydrases) optimally active at the acidic pH.
    • These enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids.
  • Vacuoles
    • Membrane-bound space found in the cytoplasm. Membrane known as tonoplast.
    • It contains water, sap, excretory product and other materials not useful for the cell.
    • In plant cells the vacuoles are very large.
    • In plants, the tonoplast facilitates the transport of a number of ions and other materials against concentration gradients into the vacuole.
    • In Amoeba the contractile vacuole is important for excretion.
    • In many cells food vacuoles are formed by engulfing the food particles.

 

  • Ribosome
    • first observed under the electron microscope by George Palade.
    • They are composed of ribonucleic acid (RNA) and proteins.
    • Not Bounded by any membrane.
    • The eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S.

(‘S’ stands for the sedimentation coefficient).

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  • Cytoskeleton
    • An elaborate network of filamentous proteinaceous structures present in the cytoplasm
    • Functions are mechanical support, motility, maintenance of the shape of the cell.
  • Cilia and Flagella
    • They are hair like outgrowths of cell membrane responsible for locomotion and movement of cell.
    • Cilia are small structures which work like oars, causing the movement of either the cell or the surrounding fluid. Flagella are comparatively longer.
    • Eukaryotic cilium and flagellum are covered with plasma membrane.
    • Their core called the axoneme, possesses a number of microtubules running parallel to the long axis. The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. (9+2)
    • Both the cilium and flagellum emerge from centriole-like structure called the basal bodies.

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  • Centrosome and centriole
    • Centrosome is an organelle usually containing two perpendicularly lying centrioles surrounded by amorphous pericentriolar materials.
    • Centriole has an organisation like the cartwheel. They are made up of nine evenly spaced triplet peripheral fibrils of tubulin.
    • The central part of the centriole is also proteinaceous and called the hub, connected with peripheral tubules by radial
    • The centrioles form the basal body of cilia or flagella, and spindle fibres that give rise to spindle apparatus during cell division in animal cells.

 

  • Microbodies
    • Many membrane bound minute vesicles called microbodies that contain various enzymes.
    • They are present in both plant and animal cells.

 

  • Nucleus
    • first described by Robert Brown.
    • the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming.
    • The interphase nucleus has nucleoprotein fibres called chromatin, nuclear matrix and one or more spherical bodies called
    • the nuclear envelope is consists of two parallel membranes with a space inbetween called perinuclear space.
    • The outer membrane usually remains continuous with the endoplasmic reticulum and also bears ribosomes on it.
    • At a number of places the nuclear envelope is interrupted by minute pores. These nuclear pores provide passages for movement of RNA and protein molecules.
    • Normally, there is only one nucleus per cell.Some mature cells even lack nucleus, e.g., erythrocytes of many mammals and sieve tube cells of vascular plants.
    • The nuclear matrix or the nucleoplasm contains nucleolus and chromatin.
    • The nucleoli are spherical structures present in the nucleoplasm. It is non-membrane bound. It is a site for active ribosomal RNA synthesis.
    • During cell division, chromatin network condenses into c
    • Chromatin contains DNA and some basic proteins called histones, some non-histone proteins and also RNA.
    • Every chromosome essentially has a primary constriction or the centromere on the sides of which disc shaped structures called kinetochores are present.

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  • Sometimes a few chromosomes have non-staining secondary constrictions at a constant location. This gives the appearance of a small fragment called the satellite.

 

 

PRINTABLE Pdf file of chapter notes are available…please click on the link…

chapter 8 – cell NCERT

 

 

 

 

 

CHAPTER 7: STRUCTURAL ORGANISATION IN ANIMALS

CHAPTER 7

STRUCTURAL ORGANISATION IN ANIMALS

  • A group of similar cells of common origin along with intercellular substances performing a specific function is known as tissue.
  • Animal tissues are broadly classified into four types: (i) Epithelial, (ii) Connective, (iii) Muscular and (iv) Neural.

 

Tissue Origin Function
Epithelial Ecto, meso, endodermal Protection, absorption, secretion etc.
Connective Mesodermal To connect, support, transport etc
Muscular Mesodermal Locomotion and movement
Nervous Ectodermal Control and coordination

 

Epithelial Tissue

This tissue has a free surface, which faces either a body fluid or the outside environment and thus provides a covering or a lining for some part of the body.

The cells are compactly packed with little intercellular matrix.

There are two types of epithelial tissues namely simple epithelium and compound epithelium. Simple epithelium –

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Connective Tissue

Connective tissues are most abundant and widely distributed in the body of complex animals.

They are named connective tissues because of their special function of linking and supporting other tissues/organs of the body.

In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin which provide strength, elasticity and flexibility to the tissue.

These cells also secrete modified polysaccharides, which accumulate between cells and fibres and act as matrix (ground substance).

Connective tissues are classified into three types: (i) Loose connective tissue, (ii) Dense connective tissue and (iii) Specialised connective tissue.

 

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Muscle Tissue

  • Each muscle is made of many long, cylindrical fibres arranged in parallel arrays. These fibres are composed of numerous fine fibrils, called myofibrils.
  • Muscle fibres contract (shorten) in response to stimulation, then relax (lengthen) and return to their uncontracted state in a coordinated fashion.
  • Their action moves the body to adjust to the changes in the environment and to maintain the positions of the various parts of the body.
  • In general, muscles play an active role in all the movements of the body.
  • Muscles are of three types, skeletal, smooth, and cardiac.

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 Neural Tissue

  • Neural tissue consists of neuron and neuroglial cells.
  • Neural tissue exerts the greatest control over the body’s responsiveness to changing conditions.
  • Neuron, an excitable cell is the unit of neural system.
  • The neuroglial cells which constitute the rest of the neural system protect and support neurons.
  • Neuroglia make up more than one half the volume of neural tissue in our body.
  • When a neuron is suitably stimulated, an electrical disturbance is generated which swiftly travels along its plasma membrane.
  • Arrival of the disturbance at the neuron’s endings, or output zone, triggers events that may cause stimulation or inhibition of adjacent neurons and other cells

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 ORGAN AND ORGAN SYSTEM

  • Tissues organise to form organs which in turn associate to form organ systems in the multicellular organisms, this results in more efficient and coordinated system of cells.
  • Each organ is made of one or more type of tissues.
  • Complexity in organ and organ systems displays certain evolutionary trend.


EARTHWORM

Habits and habitat –

  • Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil.
  • During day time, they live in burrows made by boring and swallowing the soil. In the gardens, they can be traced by their faecal deposits known as worm castings.
  • The common Indian earthworms are Pheretima and

Morphology

  • Long cylindrical body.
  • Body is divided into many short segments which are similar (metameres about 100-120).
  • Body surfaces –

    • The dorsal surface of the body is marked by a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body.
    • The ventral surface is distinguished by the presence of genital openings (pores).
    • Anterior end consists of the mouth and the prostomium, a lobe which serves as a covering for the mouth and as a wedge to force open cracks in the soil into which the earthworm may crawl. The prostomium is sensory in function.
  • Segments and their related structures –

    • The first body segment is called the peristomium (buccal segment) which contains the mouth.
    • In a mature worm, 14th, 15th, 16th segments are covered by a prominent dark band of glandular tissue called clitellum. Thus the body is divisible into three prominent regions – preclitellar, clitellar and postclitellar segments.
    • Four pairs of spermathecal apertures are situated on the ventro-lateral sides of the intersegmental grooves, i.e., 5th -9th
    • A single female genital pore is present in the mid-ventral line of 14th
    • A pair of male genital pores are present on the ventro-lateral sides of the 18th
    • Numerous minute pores called nephridiopores open on the surface of the body.
    • In each body segment, except the first, last and clitellum, there are rows of S-shaped setae, embedded in the epidermal pits in the middle of each segment. Setae can be extended or retracted. Their principal role is in locomotion.

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 Anatomy

Body Wall

  • Layers are outermost thin non-cellular cuticle, epidermis, two muscle layers (circular and longitudinal) and an innermost coelomic epithelium
  • The epidermis is made up of a single layer of columnar epithelial cells which contain secretory gland cells.

Alimentary canal

  • It is a straight tube and runs between first to last segment of the body.
  • It consists of a terminal mouth, buccal cavity (1-3 segments), muscular pharynx, oesophagus (5-7 segments), muscular gizzard (8-9 segments), stomach (9-14 segments), intestine (15th to last segment), anus.
  • Gizzard helps in grinding the soil particles and decaying leaves.
  • Calciferous glands, present in the stomach, neutralise the humic acid present in humus.
  • A pair of short and conical intestinal caecae project from the intestine on the 26th segment.
  • In intestine between 26-35 segments, an internal median fold of dorsal wall called typhlosole is present. It increases the effective area of absorption in the intestine.

Circulatory system

  • Pheretima exhibits a closed type of blood vascular system, consisting of blood vessels, capillaries and heart.
  • Blood is confined to the heart and blood vessels. Contractions keep blood circulating in one direction. Smaller blood vessels supply the gut, nerve cord, and the body wall.
  • Blood glands are present on the 4th, 5th and 6th segments. They produce blood cells and haemoglobin which is dissolved in blood plasma.
  • Blood cells are phagocytic in nature.

Respiratory system

  • Earthworms lack specialised breathing devices.
  • Respiratory exchange occurs through moist body surface into their blood stream.

Excretory system

  • The excretory organs occur as segmentally arranged coiled tubules called nephridia.
  • They are of three types (similar in structure) :
    1. septal nephridia – Present on both the sides of intersegmental septa of segment 15 to the last that open into intestine.
    2. integumentary nephridia – attached to lining of the body wall of segment 3 to the last that open on the body surface
    3. pharyngeal nephridia – Present as three paired tufts in the 4th, 5th and 6th segments.
  • Nephridia regulate the volume and composition of the body fluids. (osmotic regulation).
  • A nephridium starts out as a funnel that collects excess fluid from coelomic chamber. The funnel connects with a tubular part of the nephridium which delivers the wastes through a pore to the surface in the body wall into the digestive tube.

Nervous system

  • It is basically represented by ganglia arranged segmentwise on the ventral paired nerve cord.
  • The nerve cord in the anterior region (3rd and 4th segments) bifurcates, laterally encircling the pharynx and joins the cerebral ganglia dorsally to form a nerve ring.
  • The cerebral ganglia alongwith other nerves in the ring integrate sensory input as well as command muscular responses of the body.

Sense organs

  • eyes are absent but does possess light and touch sensitive organs.
  • Worms have specialised chemoreceptors (taste receptors) which react to chemical stimuli.
  • These sense organs are located on the anterior part of the worm.

Reproductive system

  • Earthworm is hermaphrodite (bisexual), i.e., testes and ovaries are present in the same individual.
  • Male –
    • two pairs of testes (10th, 11th segments).
    • Their vasa deferentia run up to the 18th segment where they join the prostatic duct.
    • Two pairs of accessory glands are present (in the 17th, 19th segments).
    • The common prostrate and spermatic duct (vary differential) opens to the exterior by a pair of male genital pores on the ventro-lateral side of the 18th
  • Female –
    • Four pairs of spermathecae are located in 6th-9th segments (one pair in each segment). They receive and store spermatozoa during copulation.
    • One pair of ovaries is attached at the inter-segmental septum of the 12th and 13th
    • Ovarian funnels are present beneath the ovaries which continue into oviduct, join together and open on the ventral side as a single median female genital pore on the 14th segment.
  • Fertilization –
    • It is a protandrous animal with crossfertilisation.
    • A mutual exchange of sperm occurs between two worms during mating. One worm has to find another worm and they mate juxtaposing opposite gonadal openings exchanging packets of sperms called spermatophores.
    • Mature sperm and egg cells and nutritive fluid are deposited in cocoons produced by the gland cells of clitellum.
    • Fertilisation and development occur within the cocoons which are deposited in soil.
    • The ova (eggs) are fertilised by the sperm cells within the cocoon which then slips off the worm and is deposited in or on the soil.
    • The cocoon holds the worm embryos.
    • After about 3 weeks, each cocoon produces two to twenty baby worms with an average of four.
    • Earthworms development is direct, i.e., there is no larva formed.

Economical uses –

  • Earthworms are known as ‘friends of farmers’ because they make burrows in the soil and make it porous which helps in respiration and penetration of the developing plant roots. The process of increasing fertility of soil by the earthworms is called vermicomposting.
  • They are also used as bait in game fishing.

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 COCKROACH

  • Brown or black bodied animals.
  • Included in class Insecta of Phylum Arthropoda.
  • Bright yellow, red and green coloured cockroaches have also been reported in tropical regions.
  • Size ranges from ¼ inches to 3 inches (0.6-7.6 cm) and have long antenna, legs and flat extension of the upper body wall that conceals head.
  • Nocturnal, Omnivores that live in damp places throughout the world.
  • They have become residents of human homes and thus are serious pests and vectors of several diseases.

Morphology

  • Scientific name of the common species of cockroach, Periplaneta Americana.
  • They are about 34-53 mm long with wings that extend beyond the tip of the abdomen in males.
  • The body of the cockroach is segmented and divisible into three distinct regions – head, thorax and abdomen.
  • The entire body is covered by a hard chitinous exoskeleton (brown in colour).
  • In each segment, exoskeleton has hardened plates called sclerites (tergites dorsally and sternites ventrally) that are joined to each other by a thin and flexible articular membrane (arthrodial membrane).
  • Head –

    • Head is triangular in shape and lies anteriorly at right angles to the longitudinal body axis.
    • It is formed by the fusion of six segments and shows great mobility in all directions due to flexible neck.
    • The head capsule bears a pair of compound eyes, a pair of thread like antennae which arise from membranous sockets lying in front of eyes. Antennae have sensory receptors that help in monitoring the environment.
    • At anterior end of the head, appendages forming biting and chewing type of mouth parts are present. The mouthparts consisting of a labrum (upper lip), a pair of mandibles, a pair of maxillae and a labium (lower lip).
    • A median flexible lobe, acting as tongue (hypopharynx), lies within the cavity enclosed by the mouthparts
  • Thorax –

    • It consists of three parts – prothorax, mesothorax and metathorax.
    • The head is connected with thorax by a short extension of the prothorax known as the neck.
    • Each thoracic segment bears a pair of walking legs.
    • The first pair of wings arises from mesothorax and the second pair from metathorax. Forewings (mesothoracic) called tegmina are opaque dark and leathery and cover the hind wings when at rest. The hind wings are transparent, membranous and are used in flight.
  • Abdomen –

    • The abdomen in both males and females consists of 10 segments.
    • In females, the 7th sternum is boat shaped and together with the 8th and 9th sterna form a brood or genital pouch whose anterior part contains female gonopore, spermathecal pores and collateral glands.
    • In males, genital pouch or chamber lies at the hind end of abdomen bounded dorsally by 9th and 10th terga and ventrally by the 9th It contains dorsal anus, ventral male genital pore and gonapophysis.
    • Males bear a pair of short, threadlike anal styles which are absent in females.
    • In both sexes, the 10th segment bears a pair of jointed filamentous structures called anal cerci.

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 Anatomy

  • Digestive system –

    • The alimentary canal is divided into three regions: foregut, midgut and hindgut.
    • Fore gut –
      • Consist of mouth, pharynx, oesophagus, crop, gizzard (Proventriculus).
      • Crop is sac like structure for storing of food.
      • Gizzard has an outer layer of thick circular muscles and thick inner cuticle forming six highly chitinous plate called teeth. Gizzard helps in grinding the food particles.
      • The entire foregut is lined by cuticle.
    • Mid gut –
      • A ring of 6-8 blind tubules called hepatic or gastric caecae is present at the junction of foregut and midgut, which secrete digestive juice.
    • Hind gut –
      • At the junction of midgut and hindgut 100-150 yellow coloured thin filamentous Malphigian tubules are present. They help in removal of excretory products from haemolymph.
      • The hindgut is broader than midgut and is differentiated into ileum, colon and rectum.
      • The rectum opens out through anus.
  • Blood vascular system –
    • Open type circulatory system.
    • Blood vessels are poorly developed and open into space (haemocoel).
    • Visceral organs located in the haemocoel are bathed in blood (haemolymph).
    • The haemolymph is composed of colourless plasma and haemocytes.
    • Heart of cockroach consists of elongated muscular tube lying along mid dorsal line of thorax and abdomen.
    • It is differentiated into funnel shaped chambers with ostia on either side.
    • Blood from sinuses enter heart through ostia and is pumped anteriorly to sinuses again.
  • Respiratory system –
    • consists of a network of trachea, that open through 10 pairs of small holes called spiracles present on the lateral side of the body.
    • Thin branching tubes (tracheal tubes subdivided into tracheoles) carry oxygen from the air to all the parts.
    • The opening of the spiracles is regulated by the sphincters.
    • Exchange of gases take place at the tracheoles by diffusion.
  • Excretory system –
    • Excretion is performed by Malpighian tubules.
    • Each tubule is lined by glandular and ciliated cells.
    • They absorb nitrogenous waste products and convert them into uric acid which is excreted out through the hindgut. Therefore, this insect is called uricotelic.
    • In addition, the fat body, nephrocytes and urecose glands also help in excretion.
  • Nervous system –
    • It consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side. Three ganglia lie in the thorax, and six in the abdomen.
    • The nervous system of cockroach is spread throughout the body.
    • The head holds a bit of a nervous system while the rest is situated along the ventral (belly-side) part of its body. So, if the head of a cockroach is cut off, it will still live for as long as one week.
    • In the head region, the brain is represented by supra-oesophageal ganglion which supplies nerves to antennae and compound eyes.
  • Sense organs –
    • In cockroach, the sense organs are antennae, eyes, maxillary palps, labial palps, anal cerci, etc.
    • The compound eyes are situated at the dorsal surface of the head. Each eye consists of about 2000 hexagonal ommatidia. With the help of several ommatidia, a cockroach can receive several images of an object. This kind of vision is known as mosaic vision with more sensitivity but less resolution, being common during night (hence called nocturnal vision).
  • Reproductive system –
    • Cockroaches are dioecious and both sexes have well developed reproductive organs.
    • Male reproductive system –
      • It consists of a pair of testes (in the 4th -6th abdominal segments), vas deferens, ejaculatory duct, seminal vesicle.
      • The ejaculatory duct opens into male gonopore situated ventral to anus.
      • A characteristic mushroom shaped gland is present in the 6th-7th abdominal segments which functions as an accessory reproductive gland.
      • The external genitalia are represented by male gonapophysis or phallomere (chitinous asymmetrical structures, surrounding the male gonopore).
      • The sperms are stored in the seminal vesicles and are glued together in the form of bundles called spermatophores which are discharged during copulation.
    • Female reproductive system –
      • It consists of two large ovaries (2nd – 6th abdominal segments), oviducts, vagina, genital chamber, spermathecal.
      • Each ovary is formed of a group of eight ovarian tubules or ovarioles, containing a chain of developing ova.
      • A pair of spermatheca is present in the 6th segment which opens into the genital chamber.
      • Sperms are transferred through spermatophores.
    • Fertilization and development –
      • Fertilization internal.
      • Fertilized eggs are encased in capsules called oothecae. Ootheca is a dark reddish to blackish brown capsule, about 3/8″ (8 mm) long.
      • They are dropped or glued to a suitable surface, usually in a crack or crevice of high relative humidity near a food source.
      • On an average, females produce 9-10 oothecae, each containing 14-16 eggs.
      • The development of americana is paurometabolous, meaning there is development through nymphal stage. The nymphs look very much like adults. The nymph grows by moulting about 13 times to reach the adult form.
      • The next to last nymphal stage has wing pads but only adult cockroaches have wings.

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FROGS

Habits and habitat

  • Frogs can live both on land and in freshwater and belong to class Amphibia of phylum Chordata.
  • Most common species of frog found in India is Rana tigrina.
  • They do not have constant body temperature i.e.; their body temperature varies with the temperature of the environment. Such animals are called cold blooded or poikilotherms.
  • They have the ability to change the colour to hide them from their enemies (camouflage). This protective coloration is called mimicry.
  • They take shelter in deep burrows to protect them from extreme heat and cold. This is called as summer sleep (aestivation) and winter sleep (hibernation).

Morphology

  • The skin is smooth and slippery due to the presence of mucus. The skin is always maintained in a moist condition.
  • The colour of dorsal side of body is generally olive green with dark irregular spots. On the ventral side the skin is uniformly pale yellow.
  • The frog never drinks water but absorb it through the skin.
  • Body of a frog is divisible into head and trunk. A neck and tail are absent.
  • Above the mouth, a pair of nostrils is present.
  • Eyes are bulged and covered by a nictitating membrane that protects them while in water.
  • On either side of eyes, a membranous tympanum (ear) receives sound signals.
  • The forelimbs and hind limbs help in swimming, walking, leaping and burrowing. The hind limbs end in five digits and they are larger and muscular than fore limbs that end in four digits.
  • Feet have webbed digits that help in swimming.
  • Frogs exhibit sexual dimorphism. Male frogs can be distinguished by the presence of sound producing vocal sacs and also a copulatory pad on the first digit of the fore limbs which are absent in female frogs.

Anatomy

  • Digestive System –

    • It consists of alimentary canal and digestive glands.
    • The alimentary canal is short because frogs are carnivores and hence the length of intestine is reduced.
    • Alimentary canal consists of mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum and cloaca.
    • Food is captured by the bilobed tongue.
    • Digestion of food takes place by the action of HCl and gastric juices secreted from the walls of the stomach.
    • Partially digested food called chyme is passed from stomach to the first part of the intestine, the duodenum.
    • Liver secretes bile that is stored in the gall bladder.
    • Pancreas produces pancreatic juice containing digestive enzymes.
    • The duodenum receives bile from gall bladder and pancreatic juices from the pancreas through a common bile duct.
    • Bile emulsifies fat and pancreatic juices digest carbohydrates and proteins.
    • Final digestion takes place in the intestine.
    • Digested food is absorbed by the numerous finger-like folds in the inner wall of intestine called villi and microvilli.
    • The undigested solid waste moves into the rectum and passes out through cloaca.
  • Respiratory system –

    • Frogs respire on land and in the water by two different methods.
    • In water, skin acts as aquatic respiratory organ (cutaneous respiration). Dissolved oxygen in the water is exchanged through the skin by diffusion.
    • On land, the buccal cavity, skin and lungs act as the respiratory organs.
    • The respiration by lungs is called pulmonary respiration. The lungs are a pair of elongated, pink coloured sac-like structures present in the upper part of the trunk region (thorax). Air enters through the nostrils into the buccal cavity and then to lungs.
    • During aestivation and hibernation gaseous exchange takes place through skin.
  • Circulatory system –

    • The vascular system of frog is well-developed closed type.
    • Frogs have a lymphatic system also.
    • The blood vascular system involves heart, blood vessels and blood.
    • The lymphatic system consists of lymph, lymph channels and lymph nodes.
    • Heart is a muscular structure situated in the upper part of the body cavity.
    • It has three chambers, two atria and one ventricle and is covered by a membrane called pericardium.
    • A triangular structure called sinus venosus joins the right atrium. It receives blood through the major veins called vena cava.
    • The ventricle opens into a saclike conus arteriosus on the ventral side of the heart.
    • The blood from the heart is carried to all parts of the body by the arteries (arterial system).
    • The veins collect blood from different parts of body to the heart and form the venous system.
    • Special venous connection between liver and intestine as well as the kidney and lower parts of the body are present in frogs. The former is called hepatic portal system and the latter is called renal portal system.
    • The blood is composed of plasma and cells.
    • The blood cells are RBC (red blood cells) or erythrocytes, WBC (white blood cells) or leucocytes and platelets.
    • RBC’s are nucleated and contain red coloured pigment namely haemoglobin.
    • The lymph is different from blood.
    • It lacks few proteins and RBCs.
    • The blood carries nutrients, gases and water to the respective sites during the circulation.
    • The circulation of blood is achieved by the pumping action of the muscular heart.
  • Excretory system –

    • The elimination of nitrogenous wastes is carried out by a well-developed excretory system.
    • The excretory system consists of a pair of kidneys, ureters, cloaca and urinary bladder.
    • Kidneys are compact, dark red and bean like structures situated a little posteriorly in the body cavity on both sides of vertebral column.
    • Each kidney is composed of several structural and functional units called uriniferous tubules or nephrons.
    • Two ureters emerge from the kidneys in the male frogs. The ureters act as urinogenital duct which opens into the cloaca.
    • In females the ureters and oviduct open seperately in the cloaca.
    • The thin-walled urinary bladder is present ventral to the rectum which also opens in the cloaca.
    • The frog excretes urea and thus is a ureotelic
    • Excretory wastes are carried by blood into the kidney where it is separated and excreted.
  • Endocrine system-

    • The chemical coordination of various organs of the body is achieved by hormones which are secreted by the endocrine glands.
    • The prominent endocrine glands found in frog are pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals and gonads.
  • Nervous system –

    • The nervous system is organised into a central nervous system (brain and spinal cord), a peripheral nervous system (cranial and spinal nerves) and an autonomic nervous system (sympathetic and parasympathetic).
    • There are ten pairs of cranial nerves arising from the brain.
    • Brain is enclosed in a bony structure called brain box (cranium).
    • The brain is divided into fore-brain, mid-brain and hind-brain.
    • Forebrain includes olfactory lobes, paired cerebral hemispheres and unpaired diencephalon.
    • The midbrain is characterised by a pair of optic lobes.
    • Hind-brain consists of cerebellum and medulla oblongata.
    • The medulla oblongata passes out through the foramen magnum and continues into spinal cord, which is enclosed in the vertebral column.
  • Sense organs –

    • Frog has different types of sense organs, namely organs of touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (eyes) and hearing (tympanum with internal ears).
    • Eyes and internal ears are well-organised structures and the rest are cellular aggregations around nerve endings.
    • Eyes in a frog are a pair of spherical structures situated in the orbit in skull. These are simple eyes (possessing only one unit).
    • External ear is absent in frogs and only tympanum can be seen externally. The ear is an organ of hearing as well as balancing (equilibrium).
  • Reproductive system –

    • Frogs have well organised male and female reproductive systems.
    • Male reproductive system –
      • It consists of a pair of yellowish ovoid testes, which are found adhered to the upper part of kidneys by a double fold of peritoneum called mesorchium.
      • Vasa efferentia are 10-12 in number that arise from testes.
      • They enter the kidneys on their side and open into Bidder’s canal.
      • Finally, it communicates with the urinogenital duct that comes out of the kidneys and opens into the cloaca.
      • The cloaca is a small, median chamber that is used to pass faecal matter, urine and sperms to the exterior.
    • Female reproductive system –
      • It includes a pair of ovaries. The ovaries are situated near kidneys and there is no functional connection with kidneys.
      • A pair of oviduct arising from the ovaries opens into the cloaca separately.
      • A mature female can lay 2500 to 3000 ova at a time.
    • Fertilisation and development –
      • Fertilization is external and takes place in water.
      • Development involves a larval stage called tadpole.
      • Tadpole undergoes metamorphosis to form the adult.

Economic importance –

  • Frogs are beneficial for mankind because they eat insects and protect the crop.
  • Frogs maintain ecological balance because these serve as an important link of food chain and food web in the ecosystem.
  • In some countries the muscular legs of frog are used as food by man.

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CHAPTER 7

CHAPTER 6 – ANATOMY OF FLOWERING PLANTS

CHAPTER 6

ANATOMY OF FLOWERING PLANTS

  • Study of internal structure of plants is called anatomy.
  • Plants have cells as the basic unit, cells are organised into tissues and in turn the tissues are organised into organs. Different organs in a plant show differences in their internal structure.
  • Internal structures also show adaptations to diverse environments.

THE TISSUES

A tissue is a group of cells having a common origin and usually performing a common function.

Classification of tissues –

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Meristematic Tissues

  • This tissue is responsible for active cell division which results in Growth in plants.
  • Based on location and origin, Plants have different kinds of meristems.
  • Apical meristem –

The meristems which occur at the tips of roots and shoots and produce primary tissues.e.g., root and shoot apical meristem.

During the formation of leaves and elongation of stem, some cells ‘left behind’ from shoot apical meristem, constitute the axillary bud. Such buds are present in the axils of leaves and are capable of forming a branch or a flower.

  • Intercalary meristem –

The meristem which occurs between mature tissues is known as intercalary meristem.

They occur in grasses and regenerate parts removed by the grazing herbivores.

Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and contribute to the formation of the primary plant body.

  • Lateral meristem –

The meristem that occurs in the mature regions of roots and shoots of many plants, particularly those that produce woody axis and appear later than primary meristem is called the secondary or lateral meristem.

Fascicular vascular cambium, interfascicular cambium and cork-cambium are examples of lateral meristems. These are responsible for producing the secondary tissues.

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Permanent Tissues

  • The cells of the permanent tissues do not generallydivide further.
  • Permanent tissues having all cellssimilar in structure and function are called simpletissues. Permanent tissues having many differenttypes of cells are called complex tissues.

 Simple Tissues

Parenchyma –

  • It forms the majorcomponent within organs.
  • The cells of theparenchyma are generally isodiametric.
  • Their walls are thin and madeup of cellulose.
  • They may either be closely packedor have small intercellular spaces.
  • Theparenchyma performs various functions likephotosynthesis, storage, secretion.

Collenchyma –

  • It is present in layers below theepidermis (hypodermis) in dicotyledonous plants.
  • It is foundeither as a homogeneous layer or in patches.
  • Itconsists of cells which are much thickened at thecorners due to a deposition of cellulose,hemicellulose and pectin.
  • Collenchymatous cellsmay be oval, spherical or polygonal and oftencontain chloroplasts.
  • Intercellularspaces are absent.
  • They provide mechanicalsupport to the growing parts of the plant such asyoung stem and petiole of a leaf.

Sclerenchyma –

  • It consists of long, narrow cellswith thick and lignified cell walls having a few ornumerous pits.
  • They are usually dead and withoutprotoplasts.
  • It provides mechanical support to organs.
  • On the basis of variation in form,structure, origin and development, sclerenchymamay be either fibres or sclereids.
  • Fibers– these arethick-walled, elongated and pointed cells,generally occuring in groups, in various parts ofthe plant.
  • Sclereids – theseare spherical, oval orcylindrical, highly thickened dead cells with very narrow cavities (lumen). These are commonly found in the fruit walls of nuts; pulp of fruits like guava, pear and sapota; seed coats of legumes and leaves of tea.

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 Complex Tissues

Xylem –

  • Xylem functions as a conducting tissue for water and minerals from roots to the stem and leaves.
  • It also provides mechanical strength to the plant parts.
  • It is composed of four different kinds of elements, namely, tracheids, vessels, xylem fibres and xylem parenchyma.
  • Tracheids –
    • Tracheids are elongated or tube like cells with thick and lignified walls and tapering ends.
    • These are dead and are without protoplasm.
    • The inner layers of the cell walls have thickenings which vary in form.
    • In flowering plants, tracheids and vessels are the main water transporting elements.
  • Vessels –
    • Vessel is a long cylindrical tube-like structure made up of many cells called vessel members, each with lignified walls and a large central cavity.
    • The vessel cells are also devoid of protoplasm.
    • Vessel members are interconnected through perforations in their common walls.
    • Gymnosperms lack vessels intheir xylem. The presence of vessels is a characteristic featureof angiosperms.
  • Xylem fibres –
    • They have highly thickened walls and obliterated central lumens.
    • These may either be septate or aseptate.
  • Xylem parenchyma –
    • Cells are living and thin-walled,and their cell walls are made up of cellulose.
    • They store food materials in the form of starch or fat, and other substances like tannins.
    • The radial conduction of water takes place by the ray parenchymatous cells.

 

  • Primary xylem is of two types – protoxylem and metaxylem. The first formed primary xylem elements are called protoxylem and the later formed primary xylem is called metaxylem.
  1. Endarch –Instems, the protoxylem lies towards the centre (pith) and themetaxylem lies towards the periphery of the organ. This typeof primary xylem is called endarch.
  2. Exarch –In roots, the protoxylemlies towards periphery and metaxylem lies towards the centre.Such arrangement of primary xylem is called exarch.

Phloem –

  • It transports food materials, usually from leaves toother parts of the plant.
  • Phloem in angiosperms is composedof sieve tube elements, companion cells, phloem parenchyma and phloem fibres.
  • Gymnosperms have albuminous cells and sieve cells. They lack sieve tubes and companion cells.
  • Sieve tube elements –
    • They are also long, tube-like structures, arranged longitudinally and are associated with the companion cells.
    • Their end walls are perforated in a sieve-like manner to form the sieve plates.
    • A mature sieve element possesses a peripheral cytoplasm and a large vacuole but lacks a nucleus.
  • Companion cells –
    • The functions of sieve tubes are controlled by the nucleus of companion cells.
    • The companion cells are specialised parenchymatous cells, which are closely associated with sieve tube elements.
    • The sieve tube elements and companion cells are connected by pit fields present between their common longitudinal walls.
    • The companion cells help in maintaining the pressure gradient in the sieve tubes.
  • Phloem parenchyma –
    • Itis made up of elongated, tapering cylindrical cells which have dense cytoplasm and nucleus.
    • The cell wall is composed of cellulose and has pits through which plasmodesmatal connections exist between the cells.
    • The phloem parenchyma stores food material and other substances like resins, latex and mucilage.
    • Phloem parenchyma is absent in most of the monocotyledons.
  • Phloem fibres (bast fibres)
    • They are made up of sclerenchymatous cells.
    • These are generally absent in the primary phloem but are found in the secondary phloem.
    • These are much elongated, unbranched and have pointed, needle like apices.
    • The cell wall of phloem fibres is quite thick.
    • At maturity, these fibres lose their protoplasm and become dead.
    • Phloem fibres of jute, flax and hemp are used commercially.

 

  • The first formed primary phloem consists of narrow sieve tubes and is referred to as protophloem and the later formed phloem has bigger sieve tubes and is referred to as metaphloem.

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THE TISSUE SYSTEM

On the basis of their structure and location, there are three types of tissue systems.

These are the epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system.

Epidermal Tissue System

  • The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages – the trichomes and hairs.
  • Epidermis –
    • It is the outer most layer of the primary plant body.
    • It is made up of elongated, compactly arranged cells, which form a continuous layer.
    • Epidermis is usually single layered.
    • Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole.
  • Cuticle –
    • It covers the outside of the epidermis.
    • It is a waxy thick layer.
    • It prevents the loss of water.
    • Cuticle is absent in roots.
  • Stomata –
    • They are present in the epidermis of leaves.
    • Stomata regulate the process of transpiration and gaseous exchange.
    • Each stoma is composed of two bean shaped cells known as guard cells.
    • In grasses, the guard cells are dumbbell shaped.
    • The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened.
    • The guard cells possess chloroplasts and regulate the opening and closing of stomata.
    • Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells.
    • The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.
  • Epidermal appendages –
    • Roothairs – these areunicellular elongations of the epidermal cells and help absorb water andminerals from the soil.
    • Trichomes –these are present on stem. The trichomes in the shoot system are usually multicellular.They may be branched or unbranched and soft or stiff. They may evenbe secretory. The trichomes help in preventing water loss due totranspiration.

Ground Tissue System

  • All tissues except epidermis and vascular bundles constitute the ground tissue.
  • It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
  • Parenchymatous cells are usually present in cortex,pericycle, pith and medullary rays, in the primary stems and roots.
  • Inleaves, the ground tissue consists of thin-walled chloroplast containingcells and is called mesophyll.

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Vascular Tissue System

  • The vascular system consists of complex tissues,the phloem and the xylem.
  • The xylem and phloem together constitute vascular bundles.
  • In dicotyledonous stems, cambium is present between phloem and xylem. Such vascular bundles because of the presence of cambium possess the ability to form secondary xylem and phloem tissues, and hence are called open vascular bundles.
  • In the monocotyledons,the vascular bundles have no cambium present in them. Hence, since they do not form secondary tissues they are referred to as closed.
  • When xylem and phloem within a vascular bundle are arranged in an alternate manner on different radii, the arrangement is called radial such as in roots.
  • In conjoint type of vascular bundles,the xylem and phloem are situated at the same radius of vascular bundles. Such vascular bundles are common in stems and leaves. The conjoint vascular bundles usually have the phloem located only on the outer side of xylem.

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ANATOMY OF DICOTYLEDONOUS AND MONOCOTYLEDONOUS PLANTS

Dicotyledonous Root (Sunflower Root)

Epidermis –             outermost layer,many cells protrude in the form of unicellular root                                               hairs.

Cortex –                     consists of several layers of thin-walled parenchyma cells with                                                       intercellular spaces.

Endodermis –          innermost layer of the cortex. It comprises a single layer of barrel-                                               shaped cells without any intercellular spaces. The tangential as well as                                       radial walls of the endodermal cells have a deposition of water                                                         impermeable,waxy material-suberin in the form of casparian strips.

Pericycle –                 few layers of thick-walled parenchyomatous cells, Next to                                                                endodermis. Initiation of lateral roots and vascular cambium during                                            the secondary growth takes place in these cells.

Pith –                           The pith is small or inconspicuous.

Conjuctive tissue – The parenchymatous cells which lie between the xylem and                                                               the phloem are called conjuctive tissue.

Vascular bundles – Radial/alternate type. Exarch xylem. There are usually two to four                                                xylem and phloem patches. Later, a cambium ring develops between                                            the xylem and phloem.

Stele –                         All tissues on the innerside of the endodermis such as pericycle,                                                    vascular bundles and pithconstitute the stele.

 

Monocotyledonous Root

The anatomy of the monocot root is similar to the dicot root in many respects.

It has epidermis, cortex, endodermis, pericycle, vascular bundles and pith.

As compared to the dicot root, monocots have more xylem bundles (usually more than six – polyarch).

Pith is large and well developed.

Monocotyledonous roots do not undergo any secondary growth.

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Dicotyledonous Stem

Epidermis –             outermost protective layer of the stem Covered with a thin layer of                                              cuticle, it may bear trichomes and a few stomata.

Hypodermis –         consists of a few layers of collenchymatous cells just below the                                                       epidermis, which provide mechanical strength to the young stem.

Cortex –                    consist of rounded thin walled parenchymatous cells with conspicuous                                         intercellular spaces.

Endodermis –         The innermost layer of the cortex is called the endodermis. The cells of                                       the endodermis are rich in starch grains and the layer is also referred                                           to as the starch sheath.

Pericycle –                present on the inner side of the endodermis and above the phloem in                                           the form of semi-lunar patches of sclerenchyma.

VascuIr bundles – Conjoint, collateral, open type; endarch xylem; arranged in a ring.

Pith –                         A large number of rounded, parenchymatous cells with large                                                            intercellular spaces which occupy the central portion of the stem                                                  constitute the pith.

 

Monocotyledonous Stem

  • sclerenchymatous hypodermis,
  • large, undifferentiated, conspicuous parenchymatous ground tissue large number of scattered vascular bundles, each surrounded by a sclerenchymatous bundle sheath,
  • Vascular bundles are conjoint and closed. Peripheral vascular bundles are generally smaller than the centrally located ones.
  • The phloem parenchyma is absent, and water-containing cavities are present within the vascular bundles.

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Dorsiventral (Dicotyledonous) Leaf

Epidermis –                   it covers both the upper surface (adaxial epidermis) and lower                                                         surface (abaxial epidermis) of the leaf and has a conspicuous cuticle.

                                          The lower (abaxial) epidermis generally bears more stomata than                                                   the upper (adaxial) epidermis. The latter may even lack stomata.

Mesophyll –                  parenchymatous cells present between the upperand the lower                                                      epidermis. it possesses chloroplasts and carry out photosynthesis.

It has two types of cells – the palisade parenchyma andthe spongy                                              parenchyma.

Palisade parenchyma is placed adaxially and made up of elongated                                                 cells, which are arranged vertically and parallel to each other.

Spongy parenchyma made up of oval or round and loosely arranged                                               spongy parenchymatous cells. There are numerous large spaces and                                             air cavities between these cells.

Vascular system –       vascular bundles are seen in the veins and the midrib.

                                      The size of the vascular bundles are dependent onthe size of the veins.

The veins vary in thickness in the reticulate venation of the dicot leaves.

The vascular bundles are surrounded by a layer of thick walled bundle                                          sheath cells.

 

Isobilateral (Monocotyledonous) Leaf

The anatomy of isobilateral leaf is similar to that of the dorsiventral leaf in many ways.

It shows the following characteristic differences –

  • In an isobilateral leaf, the stomata are present on both the surfaces of the epidermis.
  • mesophyll is not differentiated into palisade and spongy parenchyma.
  • In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells. These are called bulliform cells. When the bulliform cells in the leaves have absorbed water and are turgid, the leaf surface is exposed. When they are flaccid due to water stress, they make the leaves curl inwards to minimise water loss.
  • The parallel venation in monocot leaves is reflected in the near similar sizes of vascular bundles (except in main veins).

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SECONDARY GROWTH

  • The growth of the roots and stems in length with the help of apical meristem is called the primary growth.
  • Apart from primary growth most dicotyledonous plants exhibit an increase in girth. This increase is called the secondary growth.
  • Secondary growth also occurs in stems and roots of gymnosperms. However, secondary growth does not occur in monocotyledons.
  • The tissues involved in secondary growth are the two lateral meristems: vascular cambium and cork cambium.
  • Secondary growth due to Vascular Cambium
  • The meristematic layer that is responsible for cutting off vascular tissues – xylem and pholem – is called vascular cambium.
  • In the young stem it is present in patches as a single layer between the xylem and phloem. Later it forms a complete ring.

Formation of cambial ring

In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafascicular cambium. The cells of medullary cells, adjoining these intra fascicular cambium become meristematic and form the inter fascicular cambium. Thus, a continuous ring of cambium is formed.

Cambium ring = inter + intrafascicular cambium

Activity of the cambial ring

  • The cambial ring becomes active and begins to cut off new cells, both towards the inner and the outer sides.
  • The cells cut off towards pith,mature into secondary xylem and the cells cut off towards periphery mature into secondary phloem.
  • The cambium is generally more active on the inner side than on the outer. As a result, the amount of secondary xylem produced is more than secondary phloem and soon forms a compact mass.
  • The primary and secondary phloems get gradually crushed due to the continued formation and accumulation of secondary xylem.
  • The primary xylem however remains more or less intact, in or around the centre.
  • At some places, the cambium forms a narrow band of parenchyma, which passes through the secondary xylem and the secondary phloem in the radial directions. These are the secondary medullary rays.

Spring wood and autumn wood

  • The activity of cambium is different in different conditions.
  • As in temperate regions, where the climatic conditions are not uniform through the year, In the spring season, cambium is very active and produces a large number of xylary elements having vessels with wider cavities. The wood formed during this season is called spring wood or early wood.
  • In winter, the cambium is less active and forms fewer xylary elements that have narrow vessels, and this wood is called autumn wood or late wood.
  • The spring wood is lighter in colour and has a lower density whereas the autumn wood is darker and has a higher density.
  • The two kinds of woods that appear as alternate concentric rings, constitute an annual ring. Annual rings seen in a cut stem give an estimate of the age of the tree.
  • Dendrochronology – study/finding age of plant with the help of annual ring.

 

Spring wood

Autumn wood

Cambium is very active. Cambium is less active.
Large no of xylary vessels are produced. Fewer xylary elements.
Vessels with wider cavities. Vessels with narrow cavities.
Lighter in color Darker in color.
Lower density Higher density.

Heartwood and sapwood

  • In old trees, the greater part of secondary xylem is dark brown due to deposition of organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils in the central or innermost layers of the stem. These substances make it hard, durable and resistant to the attacks of micro-organisms and insects. This region comprises dead elements with highly lignified walls and is called

The heartwood does not conduct water but it gives mechanical support to the stem.

  • The peripheral region of the secondary xylem, is lighter in colour and is known as the It is involved in the conduction of water and minerals from root to leaf.

Heartwood (Duramen)

Sapwood (alburnum)

Central part of secondary xylem Peripheral part of secondary xylem
Dark brown in colour Lighter in colour
deposition of organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils No deposition of organic matter.
Resistant to the attacks of micro-organisms and insect. Not Resistant to the attacks of micro-organisms and insect.
Comprises dead elements with highly lignified wall. Walls are not highly lignified.
Provide mechanical support to stem Conduction of water and minerals from roots to leaf.

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 Secondary growth due to Cork Cambium

  • As the stem continues to increase in girth due to the activity of vascular cambium, the outer cortical and epidermis layers get broken and need to be replaced to provide new protective cell layers.
  • Hence, another meristematic tissue called cork cambium or phellogen develops, usually in the cortex region.
  • Phellogen is a couple of layers thick. It is made of narrow, thin-walled and nearly rectangular cells.
  • Phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem while the inner cells differentiate into secondary cortex or
  • The cork is impervious to water due to suberin deposition in the cell wall. The cells of secondary cortex are parenchymatous.
  • Phellogen + phellem + phelloderm =
  • Due to activity of the cork cambium, pressure builds up on the remaining layers peripheral to phellogen and ultimately these layers die and slough off.
  • Bark refers to all tissues exterior to the vascular cambium (includes secondary phloem).
  • Bark that is formed early in the season is called early or soft Towards the end of the season late or hard bark is formed.
  • At certain regions, the phellogen cuts off closely arranged parenchymatous cells on the outer side instead of cork cells. These parenchymatous cells soon rupture the epidermis, forming a lens shaped openings called lenticels. Lenticels permit the exchange of gases between the outer atmosphere and the internal tissue of the stem. These occur in most woody trees.

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Secondary Growth in Roots

  • In the dicot root, the vascular cambium is completely secondary in origin.
  • It originates from the tissue located just below the phloem bundles, a portion of pericycle tissue, above the protoxylem forming a complete and continuous wavy ring, which later becomes circular.
  • Further events are similar to those already described above for a dicotyledon stem.

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CHAPTER 6 – Copy

Chapter 2- BIOLOGICAL CLASSIFICATION

CLASS 11th BIOLOGY NCERT NOTES

CHAPTER 2

BIOLOGICAL CLASSIFICATION

Earlier attempts for classification –

  • Aristotle was the earliest to attempt a more scientific basis for classification. He used simple morphological characters to classify plants into trees, shrubs and herbs. He divided animals into two groups, those which had red blood and those that did not.
  • Linnaeus gave a Two Kingdom system of classification with Plantae and Animalia

Five kingdom classification –

  • Proposed by R.H. Whittaker (1969).
  • The kingdoms defined by him were named Monera, Protista, Fungi, Plantae and
  • The main criteria for classification used by him include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

 

Table – Characteristics of the Five Kingdoms

Characters

Five Kingdoms

Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Cell wall Noncellular (Polysaccharide+ amino acid) Present in some Present (without cellulose) Present (cellulose) Absent
Nuclear membrane Absent Present Present Present Present
Body organisation Cellular Cellular Multiceullar/ loose tissue Tissue/ organ Tissue/organ/ organ system
Mode of nutrition Autotrophic (chemosynthetic and photosynthetic)  and Heterotrophic (saprophyte/ parasite) Autotrophic  (Photosynthetic) and Heterotrophic Heterotrophic (Saprophytic/ Parasitic) Autotrophic  (Photosynthetic) Heterotrophic (Holozoic/ Saprophytic etc.)

 

 

Now a classification system has evolved which reflects not only the morphological, physiological and reproductive similarities, but is also phylogenetic (based on evolutionary relationships.)

KINGDOM MONERA

  • It consists of only Bacteria.
  • Bacteria live in all types of habitat, even in extreme habitats such as hot springs, deserts, snow and deep oceans or as parasite in or on organisms.
  • Though the bacterial structure is very simple, they are very complex in behaviour.
  • Some of the bacteria are autotrophic (they synthesise their own food from inorganic substrates).
  • They may be photosynthetic autotrophic or chemosynthetic autotrophic.
  • The majority of bacteria are heterotrophs. (They do not synthesise their own food but depend on other organisms or on dead organic matter for food.)
  • Classification of bacteria according to their shape –
  1. Spherical – Coccus
  2. rod-shaped – Bacillus
  3. comma-shaped – Vibrium
  4. spiral – Spirillum

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Bacteria are also classified into – archaebacteria and eubacteria.

 Archaebacteria: (Primitive Bacteria)

  • These bacteria live in some of the most harsh habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).
  • Archaebacteria have a different cell wall structure and this feature is responsible for their survival in extreme conditions.
  • Methanogens are present in the guts of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.

Eubacteria: (True Bacteria)

  • These are characterised by the presence of a rigid cell wall, and if motile, a flagellum.

    Cynobacteria

  • Cyanobacteria (blue-green algae) have chlorophyll–a similar to green plants and are photosynthetic autotrophs.
  • The cyanobacteria are unicellular, colonial or filamentous, marine or terrestrial algae.
  • The colonies are generally surrounded by gelatinous sheath.
  • They often form blooms in polluted water bodies.

    Nitrogen fixing bacteria –

  • They fix atmospheric nitrogen in specialised cells called heterocysts, g., Nostoc and Anabaena. (heterocyst provide anaerobic condition required for N2 fixatiom)

    Chemosynthetic autotrophic bacteria –

  • They oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production.
  • They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur.

    Heterotrophic bacteria –

  • They are the mostly important decomposers.
  • Some help in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc.
  • Some are pathogens causing damage to human beings, crops, farm animals and pets.
  • Cholera, typhoid, tetanus, citrus canker are well known diseases caused by different bacteria.

    Reproduction in bacteria –

  • Bacteria reproduce mainly by fission.
  • Sometimes, under unfavourable conditions, they produce spores.
  • They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other. (Conjugation)

    Mycoplasmas –

  • These organisms completely lack a cell wall.
  • They are the smallest living cells known and can survive without oxygen.

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KINGDOM PROTISTA
 

  • All single-celled eukaryotes are placed under
  • Being eukaryotes, the protistan cell body contains a well defined nucleus and other membrane-bound organelles. Some have flagella or cilia.
  • Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.

Chrysophytes: (diatoms / golden algae /desmids).

  • Found in fresh water as well as in marine environments.
  • float passively in water currents (plankton). [plankton – passive flow, nekton – active flow]
  • Most of them are photosynthetic.
  • In diatoms the cell walls form two thin overlapping shells, which fit together as in a soap box.
  • The walls are embedded with silica and thus the walls are indestructible. Thus, diatoms have left behind large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’.
  • Being gritty this soil is used in polishing, filtration of oils and syrups.
  • Diatoms are the chief ‘producers’ in the oceans.

Dianoflagellates:

  • They are mostly marine and photosynthetic.
  • They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.
  • The cell wall has stiff cellulose plates on the outer surface.
  • Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.
  • Red dianoflagellates (Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides).
  • Toxins released by such large numbers may even kill other marine animals such as fishes.

Euglenoids:

  • Most of them are fresh water organisms found in stagnant water.
  • Instead of a cell wall, they have a protein rich layer called pellicle which makes their body flexible.
  • They have two flagella, a short and a long one.
  • Though they are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. Therefore, they are known as connecting link between plant and animal.
  • The pigments of euglenoids are identical to those present in higher plants. Example: Euglena

Slime Moulds:

  • Slime moulds are saprophytic protists.
  • The body moves along decaying twigs and leaves engulfing organic material.
  • Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet.
  • During unfavourable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their tips. The spores possess true walls. They are extremely resistant and survive for many years, even under adverse conditions. The spores are dispersed by air currents.

Protozoans

  • All protozoans are heterotrophs and live as predators or parasites.
  • There are four major groups of protozoans –

    (a) Amoeboid protozoans:

  • They move and capture their prey by pseudopodia (false feet).
  • Marine forms have silica shells on their surface.

e.g., Amoeba, Entamoeba (Parasite)

(b) Flagellated protozoans:

  • either free-living or parasitic.
  • They have flagella.
  • The parasitic forms cause diaseases such as sleeping sickness.

e.g., Trypanosoma.

(c) Ciliated protozoans:

  • Aquatic, actively moving organisms.
  • Have thousands of cilia.
  • They have a cavity (gullet) that opens to the outside of the cell surface.
  • The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet.

e.g., Paramoecium.

(d) Sporozoans:

  • These organisms have an infectious spore-like stage in their life cycle.

e.g., Plasmodium (malaria parasite).

 

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 KINGDOM FUNGI

  • organisms are heterotrophic.
  • Fungi are cosmopolitan and occur in air, water, soil and on animals and plants.
  • Structure –

    • fungi are filamentous (except yeast which is unicellular)
    • Their bodies consist of long, slender thread-like structures called hyphae. The network of hyphae is known as
    • Some hyphae are continuous tubes filled with multinucleated cytoplasm – these are called coenocytic hyphae. Others have septae or cross walls in their hyphae.
    • The cell walls of fungi are composed of chitin and polysaccharides.
  • Nutrition

    • Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes.
    • Those that depend on living plants and animals are called parasites.
    • They can also live as symbionts – in association with algae as lichens and with roots of higher plants as mycorrhiza.

 

  • Reproduction –

    • vegetative – fragmentation, fission and budding.
    • Asexual reproduction by spores called conidia or sporangiospores or zoospores.
    • sexual reproduction by oospores, ascospores and basidiospores.

The various spores are produced in distinct structures called fruiting bodies.

The sexual cycle involves the following three steps –

  1. Plasmogamy – Fusion of protoplasm between two motile or non-motile gametes.
  2. Karyogamy – Fusion of two nuclei.
  3. Meiosis – in zygote resulting in haploid spores.

When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse.

  • In some fungi the fusion of two haploid cells immediately results in diploid cells (2n). However, in other fungi (ascomycetes and basidiomycetes), an intervening dikaryophase (2 nuclei per cell) occur. Later, the parental nuclei fuse and the cells become diploid. The fungi form fruiting bodies in which reduction division occurs, leading to formation of haploid spores.

Haploid spores →fusion begin →dikaryophase →nuclei fuse →diploid body →meiosis →haploid spores.

The morphology of the mycelium, mode of spore formation and fruiting bodies form the basis for the division of the kingdom into various classes.

Phycomycetes

  • Found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants.
  • The mycelium is aseptate and coenocytic.
  • Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These spores are endogeneously produced in sporangium.
  • Zygospores are formed by fusion of two gametes. These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).

e.g., Mucor,Rhizopus (the bread mould) and Albugo (the parasitic fungi on mustard).

Ascomycetes (Sac fungi)

  • multicellular (except Yest)
  • Mycelium is branched and septate.
  • The asexual spores are conidia produced exogenously on the special mycelium called conidiophores.
  • Sexual spores are called ascospores which are produced endogenously in sac like asci. These asci are arranged in different types of fruiting bodies called ascocarps.
  • Neurospora is used extensively in biochemical and genetic work.
  • Many members like morels and buffles are edible and are considered delicacies.

e.g., yeast, Aspergillus,Penicillium,Claviceps and Neurospora.

Basidiomycetes (mushrooms, bracket fungi, puff balls)

  • They grow in soil, on logs and tree stumps and in living plant bodies as parasites, e.g., rusts and smuts.
  • The mycelium is branched and septate.
  • The asexual spores are generally not found.
  • vegetative reproduction commonly by fragmentation.
  • The sex organs are absent,
    • Plasmogamy is brought about by fusion of two vegetative or somatic cells of different strains or genotypes.
    • The resultant structure is dikaryotic which ultimately gives rise to basidium.
    • Karyogamy and meiosis take place in the basidium producing four basidiospores. The basidiospores are exogenously produced on the basidium. The basidia are arranged in fruiting bodies called basidiocarps.

e.g., Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus).

Deuteromycetes (imperect fungi)

  • Commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.
  • When the sexual forms of these fungi were discovered they were moved into classes they rightly belong to.
  • The deuteromycetes reproduce only by asexual spores known as conidia.
  • The mycelium is septate and branched.
  • Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in mineral cycling.

e.g., Alternaria, Colletotrichum and Trichoderma.

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 KINGDOM PLANTAE

  • Includes all eukaryotic chlorophyll containing organisms.
  • Few members are partially heterotrophic such as the insectivorous plants or parasites.

e.g., Insectivorous plants – Bladderwort and Venus fly trap.

          Parasitic Plants – Cuscuta.

  • cell wall mainly made of cellulose.
  • Plantae includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms.
  • Life cycle of plants has two distinct phases – the diploid sporophytic and the haploid gametophytic – that alternate with each other. This phenomenon is called alternation of generation.

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KINGDOM ANIMALIA

  • They directly (herbivore) or indirectly (carnivore) depend on plants for food.
  • They digest their food in an internal cavity and store food reserves as glycogen or fat.
  • Their mode of nutrition is holozoic – by ingestion of food.
  • They follow a definite growth pattern and grow into adults with definite shape and size.
  • Higher forms show elaborate sensory and neuromotor mechanism.
  • Most of them are capable of locomotion.
  • The sexual reproduction is by copulation of male and female followed by embryological development.

 

VIRUSES, VIROIDS AND LICHENS

  • Some acellular organisms like viruses, viroids and lichens are not included in the five kingdom classification of Whittaker.

Viruses

  • Viruses did not find a place in classification since they are not truly ‘living’.
  • The viruses are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.
  • Once they infect a cell they take over the machinery of the host cell to replicate themselves, killing the host.
  • The name virus that means venom or poisonous fluid was given by Pasteur.
  • D.J. Ivanowsky (1892) recognised certain microbes as causal organism of the mosaic disease of tobacco. These were found to be smaller than bacteria because they passed through bacteria-proof filters.
  • M.W. Beijerinek (1898) demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as Contagium vivum fluidum (infectious living fluid).
  • W.M. Stanley (1935) showed that viruses could be crystallised and crystals consist largely of proteins. They are inert outside their specific host cell.
  • Viruses are obligate parasites.
  • In addition to proteins viruses also contain genetic material that could be either RNA or DNA. No virus contains both RNA and DNA.
  • A virus is a nucleoprotein and the genetic material is infectious.
  • In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA.
  • Bacterial viruses or bacteriophages (viruses that infect the bacteria) are usually double stranded DNA viruses.
  • The protein coat called capsid made of small subunits called capsomeres, protects the nucleic acid.
  • These capsomeres are arranged in helical or polyhedral geometric forms.
  • Viruses cause diseases like mumps, small pox, herpes, influenza, AIDS.
  • In plants, the symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.

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Viroids

  • Dicovered by T.O. Diener in 1971.
  • It was smaller than viruses and caused potato spindle tuber disease.
  • It was found to be a free RNA; it lacked the protein coat that is found in viruses, hence the name viroid.
  • The RNA of the viroid was of low molecular weight.

 Lichens

  • Lichens are symbiotic associations (mutually useful) between algae and fungi.
  • The algal component is known as phycobiont and fungal component as mycobiont, which are autotrophic and heterotrophic, respectively.
  • Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner.
  • So close is their association that if one saw a lichen in nature one would never imagine that they had two different organisms within them.
  • Lichens are very good pollution indicators – they do not grow in polluted areas.(Sulphur indicator).

 

Full file in Pdf form is below –

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