CBSE CLASS 11 CHAPTER 2 NOTES

 

CHAPTER 2

CBSE BIOLOGY
CLASS 11

CHAPTER 2

BIOLOGICAL CLASSIFICATION

INTRODUCTION

·        Ancient times – attempts were made to classify living organisms

·        But earlier – classification was not based on scientific criteria

·        Classification was based on their use – food, shelter & clothing

 

FIRST SCIENTIFIC CLASSIFICATION

·        Aristotle – first attempt – for scientific basis of classification

·        He classified plants – based on simple morphological characters

o   (i) Trees

o   (ii) Shrubs &

o   (iii) Herbs

·        He divided animals – 2 groups

o   (i) with red blood

o   (ii) without red blood

 

2 KINGDOM CLASSIFICATION

·        Linnaeus – 2 Kingdom system

o   (i) Plantae

o   (ii) Animalia

·        This system – did not distinguish

o   (i) Prokaryotes & Eukaryotes

o   (ii) Unicellular & Multicellular

o   (iii) Photosynthetic & Non-Photosynthetic organisms

·        There were so many organisms – which did not fall into either category

·        Therefore, 2 Kingdom classification – inadequate

·        New system was needed – included – Morphology; Other characters – Cells structure, Nature of wall, mode nutrition, habitat, methods of reproduction, evolutionary relationships, etc.,

·        Classification of organisms – undergone several changes over time

 

FIVE KINGDOM CLASSIFICATION

·        R.H. Whittaker (1969) – proposed – 5 Kingdom classification

·        5 Kingdoms – Monera, Protista, Fungi, Plantae & Animalia

·        Main criteria for classification

o   Cell structure                       -

o   Thallus Organisation

o   Mode of Nutrition - Reproduction

o   Phylogenetic relationships

·  Five Kingdom classification- brought together organisms – earlier in different Kingdoms

·       Due to change in criteria used for classification

·  Such changes may happen in future too – based on improvement in our understanding of characters & evolutionary relationships

·  Over time – classification system has evolved – that reflects not only – Morphological, physiological & reproductive similarities – but also phylogentic (evolutionary relationships)

KINGDOM MONERA

·        Bacteria – members of Kingdom Monera

·        Most abundant micro-organisms – occurs almost everywhere

·        Hundreds of Bacteria – in a handful of soil

·        Live in extreme habitats – hot springs, deserts, snow & deep oceans

·        Many of them – live as parasites – in or on other organisms

 

BACTERIA

·        4 categories – based on shape

o   (i) Spherical – Coccus (pl. Cocci)

o   (ii) Rod-shaped – Bacillus (pl. Bacilli)

o   (iii) Comma-shaped – Vibrium (pl. Vibrio)

o   (iv) Spiral-shaped – Spirillum (pl. Spirilla)

·        Structure – simple; Behaviour – Complex

·        Bacteria – show metabolic diversity

·        Some bacteria – autotrophic – prepare their own food – from inorganic substances

·        May be – photosynthetic autotrophic / Chemosynthetic autotrophic

·        Majority of bacteria – Heterotrophs – do not prepare their own food – depend on other organisms / on dead organic matter – for food

·        Phyla of Kingdom Monera – Archaebacteria & Eubacteria

ARCHAEBACTERIA

·        Special bacteria – live in most harsh habitat

o   Extreme salty areas – Halophiles

o   Hot springs – Thermoacidophiles

o   Marshy areas – Methanogens

·        They differ from other bacteria – have different cell wall structure – helps them to survive in extreme conditions

·        Methanogens – present in gut of ruminant animals – Cows & buffaloes

·        Methanogens – responsible for methane gas (Bio gas) production – from dung of these animals

EUBACTERIA

·        Thousands of Eubacteria or ‘True Bacteria’ – present

 

CHARACTERISTICS

·        Presence of rigid cell wall

·        If motile – have flagellum

 

CYANOBACTERIA       

·        Cyanobacteria (BGA) – have chlorophyll a – similar to green plants – are photosynthetic autotrophs

·        Cyanobacteria – unicellular, colonial or filamentous, marine or terrestrial algae

·        Colonies – surrounded by gelatinous sheath

·        Form blooms – in polluted water bodies

·        Some of them – fix atmospheric Nitrogen – in special cells – Heterocysts

·        Example: Nostoc & Anabaena

 

CHEMOSYNTHETIC AUTOTROPHIC BACTERIA

·        They oxidise – inorganic substances – like nitrates, nitrites & ammonia – use the released energy for ATP production

·        Help in recycling nutrients – N, P, Fe & S

 

HETEROTROPHIC BACTERIA

·        Abundant in nature

·        Majority are decomposers

·        Helps in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc.,

·        Some are pathogens – cause disease – humans, crops, farm animals & pets

·        Cholera, Typhoid, Tetanus, Citrus Canker – diseases caused by Bacteria

 

REPRODUCTION IN BACTERIA

·        Reproduce mainly by – Fission

·        Under favourable conditions – may produce spores

·        Also reproduce by – sexual reproduction – by adopting a primitive type of DNA transfer – from one bacterium to another

 

MYCOPLASMA (BACTERIA)

·        Completely lack cell wall

·        Smallest living cells

·        Can survive without oxygen

·        Many Mycoplasma – pathogenic – animals & plants

KINGDOM PROTISTA

·        All single celled eukaryotes – Protista

·        Boundaries to this Kingdom – not well defined

·        A photosynthetic protistan to one biologist – may be a plant to another

·        Some important Phyla of Kingdom Protista

(i) Chrysophytes                      

(ii) Dianoflagellates

(iii) Euglenoids              

(iv) Slime moulds

(v) Protozoans

·        Members of Protista – primarily aquatic

·        Being eukaryotes – cell body have – well defined nucleus & membrane bound organelles

·        Some have – flagella or cilia

·        Reproduce – asexually & sexually (cell fusion & zygote formation)

 

(I) CHRYSOPHYTES

·        Group includes – diatoms & golden algae (desmids)

·        Found in – Fresh & marine water

·        Microscopic & float passively in water currents (plankton)

·        Most of them – photosynthetic

 

DIATOMS

·        Diatoms – cell-walls – form 2 thin overlapping shells – fit together as in soap box

·        Silica – embedded in walls – makes it indestructible

·        Diatoms – leave behind – large amount of cell wall deposits – in their habitat – this accumulates over billions of years – called ‘Diatomaceous earth’

·        Soil – gritty – used in polishing , filtration of oils & syrups

·        Diatoms – chief producers in the oceans

 

(II) DIANOFLAGELLATES

·        Mostly marine & photosynthetic

·        Appear – yellow, green, brown, blue or red – depending on the pigment in the cell

·        Outer surface of cell wall – has stiff cellulose plates 

·        Most of them have – 2 flagella – one lies longitudinally; Other – transversely in a furrow – between wall plates

·        Very often Red dianoflagellates (Eg: Gonyaulax) – rapidly multiply – make the sea appear red (red tides)

·        Toxins released by such large numbers – may kill other marine animals (Fishes)

 

(III) EUGLENOIDS

·        Majority – fresh water organisms – found in stagnant water

·        Instead of cell wall – have protein rich layer – Pellicle – makes their body flexible

EUGLENA

·        Have 2 flagella – 1 short & 1 long

·        In the presence of sunlight – Photosynthetic

·        In the absence of sunlight – Heterotrophs – feed on other smaller organisms

·        Their pigments – identical to those in higher plants

·        Eg: Euglena

 

(IV) SLIME MOULDS

·        Saprophytic protists

·        Moves along decaying twigs & leaves – engulf organic material

SLIME MOULD

·  Under suitable condition – form aggregation called Plasmodium – grow & spread over several feet

·     Unfavourable condition – Plasmodium – differentiates to form fruiting bodies – bears spores at their tips

·        Spores – have true walls

·        Spores – extremely resistant – survive for many years – even in adverse conditions

·        Spores – dispersed by air currents

 

(V) PROTOZOANS

·        Protozoans – heterotrophs – live as predator or parasites

·        Believed to be – primitive relatives of animals

·        4 major groups

o   (a) Amoeboid protozoans

o   (b) Flagellates Protozoans

o   (c) Ciliated Protozoans

o   (d) Sporozoans

 

 (a) AMOEBOID PROTOZOANS

·        Live in fresh water, sea water or moist soil

AMOEBA

·        Move & capture their prey – using pseudopodia (false feet) – Amoeba

·        Marine forms – have Silica shells on their surface

·        Some are parasites – Eg: Entamoeba

 

 (b) FLAGELLATED PROTOZOANS

·        Either free-living or parasitic

TRYPNOSOMA

·        Have flagella

·        Parasitic forms – cause diseases

·        Eg: Trypanosoma – Sleeping sickness

 

(c) CILIATED PROTOZOANS

·        Aquatic, actively moving organisms – because of the presence of thousands of cilia

·        Have a cavity (gullet) – opens outside of the cell surface

·        Coordinated movement of rows of cilia – causes the water laden with food – steer into gullet

·        Eg: Paramoecium

(d) SPOROZOANS

·        Organisms have – infectious spore like stage in their life cycle

·        Eg: Plasmodium (Malarial Parasite) – causes malaria – affects human population

KINGDOM FUNGI

·        Heterotrophic organisms

·        Shows diversity in – Morphology & habitat

 

SOME COMMON FUNGI

·        Fungi – causes bread mould or fruits to rot

·        Common mushroom & toadstools – Fungi

·        White spots – mustard leaves – due to parasitic fungus

·        Some unicellular fungi – Eg: Yeast – used to make bread & beer

·        Fungi – causes diseases in plants & animals – Eg: Wheat rust – Puccinia

·        Source of antibiotics – Eg: Penicillium

 

HABITAT

·        Cosmopolitan – found in – air, water, soil, on plants & animals

·        Prefer to grow in – warm, humid places

·        That’s the reason we refrigerate the food – to prevent from fungal & bacterial infection

 

BODY STRUCTURE

·        Except yeast (unicellular) – fungi are filamentous

·        Body – long, slender, thread like structure – called Hyphae

·        Network of Hyphae – Mycellium

·        Some hyphae – continuous tube – filled with multinucleated cytoplasm – called Coenocytic hyphae

·        Others – have septae / cross walls – in hyphae

·        Cell walls – made of Chitin & polysaccharides

 

MYCELIUM

   

NUTRITION

·        Most Fungi – heterotrophic; absorb – soluble organic matter – from dead substances – called Saprophytes

·        Some depend on plants & animals – Parasites

·        Also live as symbionts – in association with algae – called Lichens

·        Live in association with roots of higher plants – Mycorrhiza

 

REPRODUCTION

·        Vegetative reproduction – Fragmentation, fusion & budding

·        Asexual reproduction – spores – called Conidia or Sporangiospores or Zoospores

·        Sexual reproduction – by oospores, ascospores & basidiospores

·        Various spores – produced in distinct structures – fruiting bodies

 

SEXUAL CYCLE IN FUNGI

·        3 steps

o   (i) PLASMOGAMY – fusion of protoplasms between two motile / non-motile gametes

o   (ii) KARYOGAMY – fusion of 2 nuclei

o   (iii) MEIOSIS – in zygote forms haploid spores

·  When fungus reproduces sexually – 2 haploid hyphae (compatible) – come together & fuse

·       In some fungi – this fusion immediately results in – diploid cells (2n)

·   Other fungi (ascomycetes & basidiomycetes) – intermediate stage – Dikaryotic stage (n + n – 2 nuclei per cell) – condition called Dikaryon – phase called Dikaryophase

·       Later – 2 nuclei fuse – forms diploid cells

·       Fungi – fruiting bodies – where reduction division occurs – forms haploid spores

·    On the basis of – Morphology of mycelium, mode of spore formation & fruiting body – Kingdom Fungi – divided into various classes

 

(I) PHYCOMYCETES

·        Members – found in aquatic habitat & on decaying wood in moist & damp places or as parasites on plants

MUCOR

·        Mycelium – aseptate (no septa between cells) & Coenocytic (contains many nuclei in single cytoplasm)

·        Asexual reproduction – through Zoospores (motile) or by Aplanospores (non-motile)

·        Spores – produced endogeneously in Sporangium

·        Sexual reproduction – fusion of 2 gametes – forms Zygospores

·        Gametes – similar in morphology – isogamous; or dissimilar – anisogamous / oogamous

·        Eg: Mucor, Rhizophus (bread mould), Albugo (Parasitic fungi on mustard)

 

(II) ASCOMYCETES

·        Commonly called – Sac-fungi

·        Unicellular – Eg: Yeast (Saccharomyces) or Multicellular – Eg: Penicillium

·        Saprophytic, decomposers, parasitic or coprophilous (growing on dung)

·        Mycelium – branched & septate

ASPERGILLUS

·        Asexual reproduction – through spores – Conidia – produced exogeneously on conidiospores (special mycelium)

·        Sexual reproduction – through sexual spores – ascospores – produced endogeneously in sac like structure – Asci (Singular. Ascus)

·        Asci – arranged on different fruiting bodies – Ascocarps

·        Eg: Aspergillus, Claviceps & Neurospora

·        Neurospora – used in biochemical & genetic work

·        Morels & buffels – are edible delicacies

 

                          

(III) BASIDIOMYCETES

·        Common basidiomycetes – Mushrooms, bracket fungi or puffballs

·        Grows – in soil, on logs & tree stumps & in living plants (parasites)

·        Eg: Rusts & Smuts

AGARICUS

·        Mycelium – branched & septate

·        Asexual spores – not found

·        Vegetative reproduction – by fragmentation

·        Sex organs – absent

·        Plasmogamy occurs – fusion of 2 vegetative / somative cells of different strains or genotypes – results in – dikaryotic – gives rise to basidium

·        Karyogamy & meiosis – takes place in basidium – produce 4 basidiospores

·        Basidiospores – exogeneously produced on basidium (pl. Basidia)

·        Basidia – arranged in fruiting body – Basidiocarp

·        Eg: Agaricus (Mushroom), Ustilago (Smut) & Puccinia (Rust fungus)

RUSTS

SMUTS

(IV) DEUTROMYCETES

·        Commonly called – Imperfect fungi – because only asexual / vegetative phases of this fungi are known

·        When sexual forms of these fungi were discovered – they were moved into the right classes they belong to – till then they are kept under Deutromycetes

·        When the linkages were established – fungi correctly identified – moved out of Deutromycetes

·        Once their sexual stage identified – often moved to Ascomycetes and Basidiomycetes

·        Deutromycetes – reproduce by – asexual spores – Conidia

·        Mycelium – septate & branched

·        Some are – Saprophytes or parasites

·        Many are – decomposers of litter, help in mineral cycling

·        Eg: Alternaria, Colleototrichum & Trichoderma

 

KINGDOM PLANTAE

·        Includes – all eukaryotic, chlorophyll – containing organisms – commonly called plants

·        Few members – partially heterotrophic –  Insectivorous plants or parasites

·        Insectivorous plant – Eg: Bladderwort & Venus fly trap

·        Parasite – Eg: Cuscuta

BLADDERWORT                             VENUS FLY TRAP

                        CUSCUTA

·        Plant cells – eukaryotic structure (prominant nucleus, chloroplast & membrane bound organelles), cell wall present – made of cellulose

·        Plantae includes – Algae, Bryophytes, Pteridophytes, Gymnosperms & Angiosperms

·        Life cycle of plants – 2 phases

o   (i) Diploid Sporophytic

o   (ii) Haploid Gametophytic

·        The 2 phases alternate with each other

·        Length of the phases, whether these phases – free living or dependent on others – vary according to plant groups

·        This phenomenon – Alternation of generation

 

KINGDOM ANIMALIA

·        Heterotrophic eukaryotic organisms, multicellular, cells lack cell wall

·        Directly or indirectly – depends on plants for food

·        Digests food – in internal cavity

·        Stores food reserves – as glycogen or fat

·        Mode of nutrition – holozoic – ingestion of food

·        Follow definite growth pattern – grow into adults – have a definite shape & size

·        Higher animals – show sensory & neuromotor mechanism

·        Most of them – capable of locomotion

·        Sexual reproduction – by copulation of male & female – embryological development follows

 

VIRUSES, VIROIDS & LICHENS

·        In Whittaker’s 5 kingdom classification – some acellular organisms not mentioned – Viruses & Viroids & dual organism – Lichens

 

VIRUSES

·        Viruses – no place in classification – as they are not truly ‘living’

·        Living organisms – have cell structure

·        But Virus – non-cellular organisms – have an inert crystalline structure outside the living cell

·        Once they infect a cell – take over the machinery of host cell – replicate – kill the host

 

DISCOVERIES

·        Virus – means Venom or poisonous fluid – given by – Pasteur D.J. Ivanowsky (1892) – recognised microbial organisms – of mosaic disease of tobacco

·        They were smaller than bacteria – pass through bacteria proof filters

·        M.W. Beijerinek (1898) – demonstrated – extracts from infected Tobacco plant – caused disease in healthy plants

·        Called the fluid – Contagium Vivum fluidum (infectious living fluid)

·        W.M. Stanley (1935) – viruses can be crystallised – crystals contains large amount of protein

 

GENERAL FEATURES

·        Viruses – inert outside the specific host cell

·        They are obligate parasites (cannot complete life cycle without exploiting a specific host)

·        Along with protein – they also contain genetic material – either RNA or DNA – never both

·        Virus – nucleoprotein & genetic material is infectious

·        Virus (infects plants) – single stranded RNA

·        Virus (infects animals) – Single or double stranded RNA or double stranded DNA

·        Bacterial viruses / Bacteriophages – infect bacteria – double stranded DNA viruses

·        Virus – protein coat – called Capsid – made of small subunits – Capsomeres

·        Capsid (Protein coat) – protects nucleic acid

·        Capsomeres – arranged in helical / polyhedral geometric forms

·        Viruses – causes diseases – small pox, mumps, herpes, influenza, AIDS (Humans)

·        Plant diseases – symptoms – Mosaic formation, leaf rolling & curling, yellowing, vein clearing, dwarfing & stunted growth

 

VIROIDS

·        T.O. Diener (1971) – discovered viroids – smaller than virus – causes Potato Spindle tuber disease

·        It is a free RNA, lack protein coat

·        RNA of Viroid – low molecular weight

     

LICHENS

·        Symbiotic association – i.e. mutually useful associations – between algae & fungi

·        Algal component – Phycobiont – Autotrophic

·        Fungal component – Mycobiont – Heterotrophic

·        Algae – provide food for fungi

·        Fungi – provide shelter & absorb mineral nutrients & water for algae

·        This association – very close – cannot distinguish the 2 organisms

·        Lichens – very good pollution indicators – do not grow in polluted areas

 

LICHEN