Kingdom - Plantae

 

XI  CH-3   Kingdom -   Plantae     

    

                         

1) Kingdom   Plantae=                                                             

It is further classified  

1)Phanerogams- These are commonly called seed producing plants. They produce special reproductive structures that are visible (Phaneros – visible) .

2)Cryptogams – These are spore producing plants and do not produce seeds and flowers. They reproduce sexually by gametes but sex organs are concealed (kryptos : hidden, gamos : marriage) 

A) Division : ThallophytaThese include the simplest plants which possess undifferentiated or thallus like forms,     reproductive organs single celled called gametangia. It includes only Algae. .Characteristic of  Thallophyta / Algae-   

i)Plant body is thallus, which may be unicellular, colonial, filamentous or parenchymatous.

 ii)Usually aquatic but a few are also found in moist terrestrial habitats like tree trunks, wet rocks, moist soil,   

iii)Vascular tissues and mechanical tissues are absent. 

iv) Plant body is thalloid i.e. undifferentiated into root, stem and leaves.

v)They may be small, unicellular, microscopic like Chlorella (non- motile), Chlamydomonas (motile). vi)They  can be multicellular, unbranched, filamentous like Spirogyra or branched, filamentous like Chara. Sargassum, a huge macroscopic sea weed which measures more than 60 meters in length is also an alga.

vii)Reproduction is vegetative by fragmentation, asexual by spore formation (zoospores) and sexual reproduction by fusion of two gametes which may be Isogamous (Spirogyra), Anisogamous (Chlamydomonous) or Oogamous (Volvox) Viii)Life cycle is various- haplontic, diplontic or diplohaplontic

Algae are classified as per its pigments like chlorophyll, xanthophylls and phycobilin.

a) Chlorophyceae (green algae)                                        

i)These are mostly fresh water (few brackish water and marine).

ii)Plant body is unicellular, colonial, filamentous. Cell wall contains cellulose.

iii)Chloroplasts are  of  various  shapes like discoid, plate-like, reticulate, cup-shaped, ribbon-shaped or spiral. .

iv) Photosynthetic pigments is chlorophyll a and b

v)The stored food is in the form of starch. .

vi)It is  rich in protein, so used as food;  space travellers.

vii)E.g. Chlorella. Chlamydomonas, Spirogyra, Chara, Volvox, Ulothrix etc.

b) Phaeophyceae (Brown algae) :

i)Mostly marine, rarely fresh water.

ii)Simple branched / filamentous (e.g. Ectocarpus) / profusely branched (Petalonia).

iii)Cell  wall   has   cellulose,   fucans   and algin.

iv) Photosynthetic pigments like chlorophyll-a, and c , fucoxanthin are present.

v)Mannitol, laminarin and starch are  stored  food materials.

vi)Body is usually differentiated into holdfast, stalk called stipe and leaf-like photosynthetic organ called frond.

vii)Many species of marine algae are used as food.

viii)e.g. Porphyra, Laminaria, Sargassum. Some species are used for production of hydrocolloids. e.g. Ectocarpus,F ucus, etc.

c) Rhodophyceae (Red algae) :

i) These are found in marine as well as fresh water on the surface, deep sea and brakish water.

ii)Plant body is thalloid.

iii) Photosynthetic pigments like chlorophyll  a and d ,phycoerythrin.

iv)Cell wall is made up of cellulose and pectin glued with other carbohydrates.

v)Stored food is in the form of Floridean starch.

vi)Commercially important agar-agar which is used as solidifying agent in tissue culture medium is obtained from red algae.

vii) E.g. Chondrus, Batrachospermum Porphyra, Gelidium , Gracillaria, Polysiphonia, etc.  

   

Economic importance-

i)A number of brown algae ( Laminaria, Sargassum) are used as food in some countries.

ii)Fucus and Laminaria are rich source of Iodine.

iii)Laminaria and Ascophyllum have antibiotic properties.

iv)Alginic acid is obtained from Fucus and Sargassum, which is used as emulsions.

2) Division- Bryophytes –                                                                                      

They are non-vascular mosses and liverworts that grow in moist shady region.

They are called amphibians of plants kingdom because these plants live on soil but dependent on water for sexual reproduction.

Characteristic features-

i)Live in damp and shady habitats, found to grow during rainy season on damp soil, rocks, walls, etc.

ii)Life cycle of Bryophytes shows sporophytic and gametophytic stages.

iii)The dominant phase or plant body is free living gametophyte.

iv)Roots are absent but contain rhizoids.

v)Rhizoids absorb water and minerals and also help in fixation of thallus on the substratum.

vi)Vegetative reproduction is by fragmentation, tubers, gemmae, buds etc. sex organs are multicellular and jacketed.

vii)The male sex organ is called antheridium They produce biflagellate antherozoids.

viii)The female sex organ called archegonium is flask-shaped and produces a single egg. Bryophytes are divided into two groups : liverworts and mosses.

a) Liverworts (Hepaticeae) :

i)These are lower members of Bryophyta.

ii)These are primitive group of Bryophytes.

iii)Gametophyte possesses flat plant body called thallus.

iv)The thallus is green, dorsiventral, prostrate with unicellular rhizoids. e.g. Riccia, Marchantia.

Hornworts (Anthocerotae) -                                         

i)These member possess flattened thallus.

ii)The thallus produces horny structures which are called sporophytes hence the name hornworts. e.g. Anthoceros.

b) Mosses (Musci) :

i)These are advanced members of Bryophyta which possess erect plant body.

ii)Gametophytic  phase of the life cycle includes two stages namely; protonema stage and leafy stage.

iii)The protonema is prostrate green, branched and filamentous (it is also called juvenile gametophyte).

iv)It bears many buds. Leafy stage is  produced  from  each  bud. .

v)Thus protonema helps in the vegetative propagation.

vi)The leafy stage has erect, slender stem like (Cauloid) main axis bearing spiral leaf like structures (Phylloid) .

vii)It is fixed in soil by multicellular branched rhizoids.

viii)This stage bears sex organs.

ix)Vegetative  reproduction takes place by fragmentation and budding in secondary protonema.

x)e.g. Funaria,P olytrichum,Sphagnum , etc.

Economic importance -

i)Some mosses provide food for herbivorous mammals, birds, etc.

ii) Species of Sphagnum, a moss; provides peat used as fuel.

iii)Mosses are also used as packing material for transport of living materials because  they  have significant water holding capacity.

iv)Just like lichens, mosses are the first living beings to grow on rocks.

v)They decompose rocks to form soil and make them suitable for growth  of higher plants.

vi)Dense layers of mosses help in prevention of soil erosion, thus act as soil binders.

C) Pteridophyta

(Pteron : feather, phyton : plant)

i)Evolutionarily, Pteridophytes are the first vascular and true land plants.

ii)Hence considered as the first successful terrestrial plants with true roots, stem and leaves.

iii)These plants have a primitive conducting system and they are the only Cryptogams with vascular tissues.

iv)The late Paleozoic era is regarded as the age of Pteridophytes.

vi)The group has about 400 genera and 11,000 species.

vii)The plants consist of pinnate (feather like) leaves.

viii)Leaves may   be small called microphylls (e.g. Selaginella) or large called macrophylls (e.g. Nephrolepis / fern).

ix)Pteridophytes grow in moist and shady places.

x)Pteridophytes show sporophytic and gametophytic stages in life cycle. .

xi)e.g. Ferns, Horsetail. Some are aquatic  

 (Az olla, Marsilea), xerophytic  (Equisetum) and epiphytic (Lycopodium). .

xii)Pteriodphytes show heteromorphic alternation of generations in which the sporophyte is diploid, dominant, autotrophic and independent. .

xiii)It is differentiated into root, stem and leaves. .

xiv)The primary root is short lived and soon replaced by adventitious roots while the stem may be aerial or underground. .

xv)Leaves may be scaly (Equisetum) simple and sessile (Lycopodium) or large and pinnately compound (Nephrolepis / Ferns).

xvi) In these members Xylem consists of only tracheids and Phloem consists of only sieve cells.

xvii)Secondary growth is not seen in Pteridophytes due to absence of cambium.

xviii)Pteridophytes are classified as - Psilopsida- (Psilotum), Lycopsida - (Selaginella and Lycopodium), Sphenopsida - (Equiesetum) and Pteropsida - (Dryopteris, Pteris and Adiantum)

Economic importance                                                    

Pteridophytes areUsed for medicinal purpose and as soil bindersMany varieties are grown as ornamental plants

Salient features of major plant groups under Phanerogams                                                      

A) Gymnospermae

(Gymnos : naked, sperma : seed) :-

There are about 70 genera and 1000 living species of Gymnosperms in world. In India it is represented by 16 genera and 53 species.

Characteristic features-

i)Most of the Gymnosperms are evergreen, shrubs or woody trees. .

ii)These are primitive group of flowering plants producing naked seeds.

iii)Seeds are not covered by fruit i.e. ovary.

iv)They are vascular plants having Xylem with tracheids and Phloem with sieve cells.

v)The plant body is sporophyte. It is differentiated into root, stem and leaves.

vi)The root system is tap root type. In some, roots form symbiotic association with other life forms. .

vii) Coralloid roots of Cycas show association  with blue green algae and roots  of  Pinus  show association with endophytic fungi called mycorrhizae.

viii)In Gymnosperms, stem is mostly erect, aerial, solid and cylindrical. Secondary growth is seen in Gymnosperms due to presence of cambium.

ix)In Cycas it is usually unbranched, while in conifers it is branched.  

x)The  leaves are diamorphic. The foliage leaves are green, simple needle like or pinnately compound, where as scale leaves  are small, membranous and brown.

x)Spores are produced by microsporophyll (Male) and  megasporophyll  (Female).

Economic importance - Cycas is grown as ornamental plant. Pinus is used as source of pine wood, turpentine oil and pine resin.

B)  Angiospermae (Angios : enclosed : vessel, Sperma : seed)  

1.  Angiosperms are the most advanced group of flowering plants.
2.  In these plants the seeds are enclosed within the fruit i.e. ovary. 
3. Angiosperms is a group of highly evolved plants, primarily adapted to terrestrial habitat. 
4. They vary in size. Angiosperms show heteromorphic alternation of generation in which the sporophyte is diploid, dominant, autotrophic and independent. 
5.  The gametophytes (male or female) are recessive, haploid and dependent on the sporophyte.Angiosperms are heterosporous.  
6. Microspores(commonly called pollens) are formed in microsporangia (or anthers). 
7. They develop in highly specialized microsporophyll or stamens while megaspores are formed in megasporangia (or ovules) borne on highly specialized megasporophyll called carpel. 
8.  Besides the essential whorls of microsporophylls (Androecium) and megasporophylls (Gynoecium) there are accessory whorls namely calyx (sepals) and corolla (petals) arranged together to form flowers.

Angiosperms are subdivided into two classes:

1. Embryo.They have a tap root system and the stem is branched.  
2. Leaves show reticulate venation while the flowers show tetra or pentamerous symmetry.Vascular bundles are conjoint, collateral and open type. 
3. Cambium is present between Xylem and Phloem for secondary growth.  In Dicots secondary growth is commonly found.e.g. Helianthus annus (sunflower), Hibiscusrosa-sinensis (China rose). 

B)Monocotyledonae : 

1. These plants have single cotyledon in their embryo.  
2. They have adventitious root system and stem is rarely branched.
3.  Leaves generally have sheathing leaf base and parallel venation while the flowers are generally trimerous. The vascular bundles are conjoint, collateral and closed type.
4.  In Monocots, except few plants secondary growth is absent. e.g. Zea mays (Maize), Sorghum vulgare (Jowar).

Plant life cycle and alternation of generations:

1)Life cycle of a plant includes two phases or distinct generations namely sporophyte (diploid : 2n) and gametophyte (haploid : n).

2)Some special diploid cells of sporophyte divide by meiosis to produce haploid cells.These haploid cells divide  mitotically  to  give  rise to gametophyte.

3)The gametophyte produces male and female gametes which fuse during fertilization to produce diploid zygote. It divides by mitosis to form diploid sporophyte.

4)The sporophytic and gametophytic generations generally occur alternately in the life cycle of  a plant. This phenomenon is called alternation of generations.

5)Distinct alternation of these two generations  is  observed   in   Bryophytes   and Pteridophytes.

6)In Gymnosperms and Angiosperms, gametophyte is much reduced and exists within sporophyte.

7)In algae, based upon the nature of dominant phase in life cycle, it is called haplontic, diplontic or haplo- diplontic life cycle.

8)In  Bryophytes  haploid  gametophyte is dominant.

9)It is photosynthetic, independent thalloid or erect phase Sporophyte  is short lived,  multicellular    and    depends    totally or   partially   on   gametophyte   for   nutritionand anchorage.

10)Whereas in Pteridophytes, sporophyte is dominant, independent and vascular plant body.

11)Haploid  multicellular gametophyte is generally autotrophic and short lived.

 It alternates with Sporophyte

1)Diplontic:                                                                                                                                       

i)Here mitotic divisions occurs only in diploid cells.

ii)Gametes formed through meiosis are haploid in nature.

iii)The diploid zygote   divide   mitotically.

iv)In  this  process  production of multicellular diploid organism or in the production of many diploid single cells takes place. .

v)E.g. Animals.

 2)Haplontic :

i)Here    mitosis     occurs in haploid cells.

ii)It results in the formation of single haploid cells or a multicellular haploid organism.

iii)These forms produce the gametes through mitosis.

iv)Zygote is formed After fertilization.

v)This cell is the only diploid cell in the entire life cycle of the organism.

vi)Thus the same zygotic cell later undergoes meiosis.

vii)E.g. Some Algae and Fungi.                                                                    

3)Haplo-diplontic :

i)Here mitosis occur in both diploidand haploid cells.                                                                          

ii)These organisms undergo  through a phase in which they are multicellular and haploid (the gametophyte) .

ii)a phase in which they are multicellular and  diploid (the sporophyte).

ii)E.g. Land plants and in many algae.

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