CBSE CLASS 11 CHAPTER 3 NOTES

CHAPTER 3

CBSE BIOLOGY
CLASS 11

CHAPTER 3

PLANT KINGDOM

INTRODUCTION

·          Plant kingdom – changed over time

·          Earlier classification – Fungi & members of Monera & Protista (with cell wall) – excluded from Plantae in Whittaker’s 5 Kingdom classification

·          Cyanobacteria (BGA) – not algae any more

·          Divisions of Kingdom Plantae – Algae, Bryophytes, Pteridophytes, Gymnosperms & Angiosperms 

EARLIER / ARTIFICIAL CLASSIFICATION

·          Earlier system of classification – based on morphological characters – habit, colour, number & shape of leaves, etc.,

·          Mainly based on – vegetative characters or androecium structure (Linnaeus Classification)

·          These earlier systems – artificial à they separated closely related species – as classification was based on few characters

·          Also artificial systems – gave equal weightage to – vegetative & sexual characters – not acceptable (vegetative characters easily affected by environment)

NATURAL CLASSIFICATION SYSTEMS

·          Natural Classification system – developed

·          Not only external features were considered 

·          Internal features – Ultra structure, anatomy, embryology & phytochemistry – were considered

·          Such a classification for flowering plants – given by George Bentham & Joseph Dalton Hooker (Bentham & Hooker Classification)

PHYLOGENETIC SYSTEM OF CLASSIFICATION

·          Present classification – based on evolutionary relationships – between various organisms – acceptable

·          Assumes – organisms of same taxa – have common ancestor

·          We use information from other sources – helps in classification

·          When there is no fossil evidence – these information helps

METHODS USED BY TAXONOMISTS

NUMERICAL TAXONOMY

·          Carried out using computers

·          Numbers & codes – assigned to all the characters – data is processed

·          Each & every character – given equal importance – 100s of characters considered

CYTO TAXONOMY

·          Based on cytological information – chromosome numbers, structure, behaviour

CHEMO TAXONOMY

·          Uses chemical constituents of the plants – to resolve confusion in classification

(A)    ALGAE

·          Chlorophyll-bearing, simple, thalloid (not differentiated into stem, leaves & roots), autotrophic

HABITAT

·          Largely aquatic (both fresh water & marine)

·          Found in other habitats too – moist stones, soils & wood

·          Some occur in association with fungi – Lichens

·          Association with animals (Eg: An Sloth Bear)

 

DIFFERENT FORMS OF ALGAE

·          Form & size – variable

·          Size – microscopic forms to filamentous

·          Microscopic Unicellular – Eg: Chlamydomonas

·          Colonial forms – Eg: Volvox

·          Filamentous – Eg: Ulothrix & Spirogyra

·          Few marine algae (Kelps) – form massive planting bodies

REPRODUCTION

·          Reproduction – vegetative, asexual & sexual methods

(i) VEGETATIVE REPRODUCTION

·          By fragmentation

·          Each fragment – develop into a thallus

(ii)ASEXUAL REPRODUCTION

·          By producing different kinds of spores – common spore – Zoospores – flagellated (motile) – germinate – give rise to new plants

(iii) SEXUAL REPRODUCTION

·          By fusion of 2 gametes

·          Gamete – flagellated & similar in size (Chlamydomonas) or non-flagellated & similar in size (Spirogyra)

·          Fusion of similar gametes – ‘Isogamous’

·          Fusion of 2 dissimilar gametes (dissimilar in size) – seen in some species of Chlamydomonas – ‘Anisogamous’

·          Fusion of 1 large static gamete (female) & a smaller motile gamete (male) – ‘Oogamous’ – Eg: Volvox, Fucus

IMPORTANCE OF ALGAE

·          Atleast half of the total CO₂ fixation on earth – carried out by Algae – through photosynthesis

·          They increase – level of dissolved O₂ – in their environment – as they are photosynthetic

·          They are primary producers of energy – rich components – serves as food for aquatic animals

·          Marine algae -  Porphyra, Laminaria, Sargassum, etc., - used as food

·          Marine brown algae (Eg: Algin) & red algae (Eg: Carragean) – produce large amount of – Hydrocolloids (water holding substances) – used commercially

·          Agar – commercial product – obtained from Gelidium & Gracilaria; Agar – used to grow microbes & in preparation of ice cream & jellies

·          Chlorella & Spirulina (Unicellular algae) – rich in protein – used as food supplements – even by space travellers

MAIN CLASSES OF ALGAE

·          Algae – divided into 3 main classes

o    (i) Chlorophyceae

o    (ii) Phaeophyceae

o    (iii) Rhodophyceae

(i) CHLOROPHYCEAE

·          Members – commonly called – Green Algae

·          Unicellular, colonial / filamentous

FEATURES

·          Colour – grass green – due to the dominance of pigments – Chlorophyll a & b

·          Pigments present in – Chloroplasts

·          Chloroplasts may be – discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped (in different species)

·          Most species – have one/more storage bodies – Pyrenoids in Chloroplasts

·          Pyrenoids – have protein & starch

·          Some algae – store food as – oil droplets

·          Green algae – rigid cell wall – inner layer made of cellulose; Outer layer – pectose

REPRODUCTION

·          Vegetative reproduction – by fragmentation or by formation of different spores

·          Asexual reproduction – by flagellated zoospores – produced in Zoosporangia

·          Sexual reproduction – shows variation in type & formation of sex cells

·          May be isogamous, anisogamous or oogamous

·          Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara

(ii) PHAEOPHYCEAE

·          Members – called brown algae

·          Found in – Marine habitat

FEATURES

·          Shows variation – in size & form

·          Ranges from – simple branched, filamentous forms (Eg: Ectocarpus) to profusely branched forms (Eg: Kelps) – may reach heights upto 100 metres

·          They have chlorophyll a, c, carotenoids & xanthophylls

·          Colour – varies from olive green to various shades of brown – depends on the amount of Xanthophyll pigment, Fucoxanthin present in them

·          Food – stored as complex carbohydrates – in the form of – Laminarin / Mannitol

·          Vegetative cells – cellulosic wall – covered outside by – gelatinous coating of algin

·          Protoplast – have plastids, centrally located vacuole & nucleus

·          Plant body – usually attached to substratum – by holdfast – has a stalk (stipe) – leaf-like photosynthetic organ (frond)

 

REPRODUCTION

·          Vegetative reproduction – by fragmentation

·          Asexual reproduction  - in most brown algae – by biflagellate zoospores – pear-shaped & have 2 unequal lateral flagella

·          Sexual reproduction – may be isogamous, anisogamous or oogamous

·          Union of gametes – takes place in water or within oogonium (Oogamous species)

·          Gametes – pyriform (pear-shaped) – bear 2 lateral flagella

·          Examples: Ectocarpus, Dictyota, Zaminaria, Sargassum & Fucus

(iii) RHODOPHYCEAE

·          Members – commonly called Red Algae

·          Red pigment – r-phycoerythrin – predominantly present

HABITAT

·          Majority of them – marine – mostly found in warmer areas

·          They occur both in – well-lighted regions – near water surface & also at great depths (oceans) – where less light penetrates

FEATURES

·          Most red algae – Thalli multicellular

·          Some of them – complex body organisation

·          Food – stored – floridean starch – similar to amylopectin & glycogen structure

REPRODUCTION

·          Usually by – vegetative reproduction – Fragmentation

·          Asexual reproduction – by non-motile spores

·          Sexual reproduction – by non-motile gametes

·          Oogamous (special type) – complex post fertilization developments take place

·          Eg: Polysiphonia, Porphyra, Gracilaria & Gelidium

(B)   BRYOPHYTES

·          Includes – Mosses & liverworts

HABITAT

·          Found in – moist shaded areas in the hills

·          Also called ‘Amphibians of the Plant Kingdom’ – they can live in soil but dependent on water (for sexual reproduction)

·          Plays an important role in – Plant succession – on bare rocks / soil

PLANT BODY OF BRYOPHYTES

·          Plant body – more differentiated – than algae

·          Thallus-like & prostrate or erect

·          Attached to substratum – by rhizoids (unicellular/multicellular)

·          Lack – true roots, stem or leaves

·          Posses – root-like, leaf-like or stem-like structures

·          Main plant body – haploid

·          Produce gametes – hence called gametophyte

SEX ORGANS

·          Male sex organ – Antheridium – produce biflagellate antherozoids

·          Female sex organ – Archegonium (flask shaped) – produce single egg

SEXUAL REPRODUCTION

·          Antherozoids – released into water – where they comes in contact with archegonium

·          Antherozoids – fuse with egg – produce zygote

·          Zygote – donot undergo reduction division immediately

·          Zygote – produce multicellular body – Sporophyte

·          Sporophyte – not free-living – attached to photosynthetic gametophyte & derives nutrition from it

·          Some cells in Sporophyte – undergo meiosis (reduction division) – produce haploid spores

·          Spores – germinate – produce gametophyte

IMPORTANCE OF BRYOPHYTES

·          Some mosses – provide food for – herbaceous mammals, birds & other animals

·          Sphagnum (Moss) – provide peat – used as fuel & also as packing material for transporting living material – as they have water holding capacity

·          Mosses along with lichens – colonise rocks – decompose rocks – makes substrate for growth of higher plants

·          Mosses – forms dense mat on soil – prevents soil erosion

·          Bryophytes – divided into

o    (i) Liverworts &

o    (ii) Mosses

(i) LIVERWORTS

HABITAT

·          Usually grow in – moist, shady habitat – like banks of streams, marshy grounds, damp soil, bark of trees, deep in the woods

PLANT BODY

·          Plant body – thalloid (Eg: Marchantia)

·          Thallus – dorsiventral, closely appressed to substrate

·          Leafy members – tiny leaf-like appendages present – in 2 rows – on stem-like structure

REPRODUCTION

·          Asexual reproduction – by fragmentation of thalli or by forming special structures – gemmae (sing. gemma)

·          Gemmae – green, multicellular, asexual buds – develop in gemma cups – present in thalli

·          Gemmae – detach from plant body – germinate into new individuals

SEXUAL REPRODUCTION

·          Male & female sex organs – produced either on same or different thalli

·          Sporophyte – differentiated into – foot, seta & capsule

·          After meiosis – spores produced within capsule

·          Spores – germinate – form free-living gametophytes

LIFE CYCLE OF LIVERWORT

 

(ii) MOSSES

·          Life cycle of Moss – gametophyte – predominant stage

·          Gametophyte – 2 stage

·          Protonema Stage

o    Develops directly from spore

o    Creeping, green, branched & frequently filamentous

·          Leafy Stage

o    Develops from – secondary protonema – as lateral bud

o    Have upright, slender axes – bears spirally arranged leaves

·          Attached to soil through – rhizoids – multicellular & branched

·          Sex organs – present

REPRODUCTION

·          Vegetative reproduction – by fragmentation (Mosses) & budding (Secondary protonema)

·          Sexual reproduction

·          Sex organs – antheridia & archegonia – produced at the apex of – leafy shoots

·          After fertilisation – zygote develops into sporophyte – have foot, seta & capsule

·          Sporophyte stage – elaborate than liverworts

·          Capsule – have spores – formed after meiosis

·          Have elaborate spore dispersal mechanism

·          Eg: Funaria Polythrichum & Sphagnum

(C)    PTERIDOPHYTES

·          Includes – horsetails & ferns

·          Pteridophytes – used for – medicinal purposes & as soil binders

·          Also grown as ornamentals

·          Evolutionarily – first terrestrial plants – with vascular tissues – xylem & phloem

HABITAT

·          Found in – cool, damp, shady places – some may grow well in sandy soil

PLANT BODY

·          In Bryophytes – gametophyte – dominant phase in life cycle

·          In Pteridophytes – Sporophyte – main plant body

·          Sporophyte – has true, root, stem & leaves

·          Organs – have well differentiated vascular tissues

·          Leaves – small (microphylls) – Eg: Selaginella or Large (macrophylls) – Eg: Ferns

·          Sporophytes – bear sporangia – found under leaf-like appendages – called Sporophylls

·          Some cases – Sporophylls – form compact structures – called Strobili or cones (Selaginella, Equisetum)

·          Sporangia – produce spores by meiosis – in spore mother cells

·          Spores germinate – give rise to – prothallus – inconspicuous, small but multicellular free-living, mostly photosynthetic thalloid gametophyte

·          Gametophytes grow in – cool, damp, shady place

·          Gametophyte – also require water for fertilization – therefore Pteridophytes – found in specific geographical areas

REPRODUCTION

·          Gametophyte bears – male & female sex organs

·          Male sex organ – antheridia; Female sex organ – archegonia

·          Water – required for – transfer of antherozoids (male gametes)

·          Antherozoids – released from antheridia – to the mouth of archegonium – contains egg         

·          Male gamete – fuses with egg – zygote is formed

·          Zygote – produce multicellular, well-defined sporophyte (dominant phase)

·          Majority of Pteridophytes – all spores – similar – such plants called – Homosporous

·          Some Pteridophytes (Eg: Selaginella & Salvinia) – 2 kinds of spores – macro (large) & micro (small) – Heterosporous

·          Megaspores – germinate – give rise to – female gametophyte

·          Microspores – germinate – give rise to – male gametophyte

·          Female gametophyte – retained on parent sporophyte – for variable periods

·          Development of zygote – into young embryos – occurs within female gametophyte

·          This event – precursor to – seed habit – important step in evolution

CLASSIFICATION

·          Pteridophytes – classified into 4 classes

·          Psilopsida (Psilotum)

·          Lycopsida (Selaginella, Lycopodium)

·          (iii)Sphenopsida (Equisetum)

·          Pteropsida (Dryopteris, Pteris, Adiantum)

(D)    GYMNOSPERMS

·          Gymnos – naked; Sperma – seeds

·          Plants – in which ovules – not enclosed by ovary wall – remains exposed – before & after fertilisation

·          Seeds – developed post fertilisation – not covered – i.e., naked

PLANT BODY

·          Gymnosperms – medium sized trees or tall trees & shrubs

·          Gymnosperm – giant redwood tree (Sequoia) – one of the tallest tree species

·          Roots – tap roots; in some genera – root have fungal association as Mycorrhiza (Pinus)

·          Some plants (Cycas) – special roots – Coralloid roots – associated with cyanoobacteria (N₂ fixing bacteria)

·          Stems – unbranched (Cycas) or branched (Pinus cedrus)

·          Leaves – simple or compound

·          Cycas – leaves pinnate – persist for few years

·          Gymnosperm – leaves well adapted – withstand extremes of temperature, humidity & wind

·          Conifers – needle like leaves – reduce surface area

·          Thick cuticle & sunken stomata – reduce water loss

·          Gymnosperms – heterosporous – produce haploid microspores & megaspores

·          2 kinds of spores – produced within sporangia – borne on sporophylls – arranged spirally on an axis – form lax or compact Strobili / cone

·          Strobili – bearing microsporophylls & microsporangia – called Microsporangiate / Male strobili

·          Microspores – develop into male gametophyte – highly reduced & confined to limited number of cells

·          Reduced gametophyte – pollen grain

·          Pollen grains – develop within microsporangia

·          Cones – bearing megasporophylls with ovules or megasporangia – called megasporangiate / female strobili

 

·          Male or female cones or strobili – borne on same tree (Pinus) or different tree (Cycas)

·          Megaspore mother cell – differentiated from one of the cells – of nucellus

·          Nucellus – protected by envelopes – composite structure – called ovule

·          Ovules – borne on – megasporophylls – clustered to form – female cones

·          Megaspore mother cell – undergo meiosis – form 4 megaspores

·          One megaspore – enclosed within megasporangium (Nucellus) – develops into – multicellular female gametophyte – bears 2 or more archegonia / female sex organs

·          Multicellular female gametophyte – retained with megasporangium

REPRODUCTION

·          Unlike Bryophytes & Pteridophytes – in Gymnosperms – male & female gametophyte – are not free-living

·          Male & female gametophyte – remain within sporangia – retained on sporophytes

·          Pollen grain – released from – microsporangium – carried in air current – comes in contact with – opening of ovules (on megasporophylls)

·          Pollen tube – carry male gametes – grow towards archegonia (in ovule) – release its contents – near the mouth of archegonia

·          After fertilisation à  intozygote develops into embryo; Ovules  seeds (not covered)

(E)    ANGIOSPERMS

·          Angiosperms – flowering plants

·          Pollen grains & ovules – developed in special structures – flowers

·          Unlike Gymnosperms, in angiosperms – seeds enclosed in fruits

·          Large group of plants – with wide range of habitats

·          Size – varies from tiny, almost microscopic (Wolfia) to tall trees (Eucalyptus) over 100 metres

·          They provide – food, fodder, fuel, medicines & commercial products

·          Angiosperms à 2 classes

o    Dicotyledons

o    Monocotyledons

·          DICOTYLEDONS

o    2 cotyledons in seeds

·          MONOCOTYLEDONS

o    Only 1 cotyledon in seed

SEX ORGANS

·          Male sex organ – in flower – Stamen

·          Each stamen have – slender filament with an anther at the tip

·          Anthers – undergo meiosis – produce pollen grains

·          Female sex organ – in flower – Pistil / Carpel

·          Pistil – have an ovary – with one to many ovules

·          Within ovules – embryo sacs present

·          Embryo sac à highly reduced female gametophyte

·          Embryo sac – formed by meiosis – so their cells are haploid

·          Each embryo sac – has

o    3 celled egg apparatus (1 egg & 2 synergids)

o    3 antipodal cells

o    2 polar nuclei

·          Polar nuclei – fuses to produce – secondary nucleus

REPRODUCTION

·          Pollen grains – dispersed from anthers – carried by wind or other agencies – to stigma (in pistil) – pollination

·          Pollen grains – germinate on stigma – pollen tube grows – through stigma & style – reach ovule

·          Pollen tube – enters embryo sac – 2 male gametes released

·          One male gamete – fuse with egg cell – form zygote (syngamy)

·          Other male gamete – fuse with diploid secondary nucleus – produce triploid primary endosperm nucleus (PEN) – because of 2 fusion à this event called – Double fertilisation (fusion of 2 male gametes) – unique to angiosperms

·          Zygote – develops into embryo (with 1 or 2 cotyledons)

·          PEN – develops into endosperm – provide nourishment to – developing embryo

·          Synergids & antipodals – degenerate after fertilisation

·          Post fertilisation à ovules – develop into seeds; ovaries – into fruits

PLANT LIFE CYCLE & ALTERNATION OF GENERATIONS

·          In plants – both haploid & diploid cells – divide by mitosis

·          This forms – different plant bodies – haploid & diploid

·          Haploid plant body – produce gametes – by mitosis – this plant body – called Gametophyte

·          After fertilisation – zygotes also divides by mitosis – produce diploid sporophyte plant body

·          Sporophytic plant body – produce – haploid spores – by meiosis

·           divide bySpores  mitosis – form haploid plant body once again

·          Thus, during life cycle of any sexually reproducing plant – there is alternation in generation – between – gamete producing haploid gametophyte – & spore producing diploid sporophyte

DIFFERENT PATTERNS OF ALTERNATION IN GENERATION

·          The pattern of alternation in generation differs according to plant groups

HAPLONTIC LIFE CYCLE

·          Sporophytic generation – one-celled zygote

·          Sporophytes – not free living

·          Zygote – undergo meiosis – form haploid spores

·          Haploid spores – divide by mitosis – form gametophyte

·          Gametophyte – free living – dominant photosynthetic phase

·          This kind of life cycle – Haplontic

·          Eg: Algae (Volvox & Spirogyra) some Chlamydomonas species

 

DIPLONTIC LIFE CELL

·          Diploid sporophyte – dominant, photosynthetic & independent phase

·          Gametophyte phase – single to few-celled haploid gametophyte (gametes)

·          This life cycle – Diplontic

·          Gametes – fertilise à  diploid sporophyte

·          Eg: All seed bearing plants – Gymnosperms & Angiosperms

HAPLO-DIPLONTIC LIFE CELL

·          Bryophytes & Pteridophytes – exhibit intermediate condition – Haplo-diplontic

·          Both phases – multicellular & often free living – differ in dominant phases

·          (a) Haploid gametophyte (thalloid /erect) – dominant, independent, photosynthetic

·          Alternates with – diploid sporophyte – short-lived, multicellular

·          Sporophyte – totally / partially dependent on – gametophyte – for anchorage & nutrition

·          Eg: All Bryophytes

·           (b) Diploid sporophyte – dominant, independent, photosynthetic, vascular plant body

·          Alternates with – Haploid gametophyte – multicellular, saprophytic/autotrophic, independent, but short lived

·          Eg: All Pteridophytes

 

·          Most algae – Haplontic; some of them (Eg: Ectocarpus, Polysiphonia, Kelps) – Haplo-diplontic

·          Fucus (Alga) - Diplontic