Biology: Plant Kingdom

 PLANT KINGDOM

·         Artificial classification – oldest classification and it is based on few vegetative and sexual characters.

·         Natural classification system  – it is based on natural affinities among the organisms  in their external and internal features.

·         Phylogenetic classification system – it is based on evolutionary relationship

·         Numerical taxonomy – by using computers numbers and codes are assigned to all the characters and data are processed.

·         Cytotaxonomy – it is based on cytological information like chromosome number, structure and behavior.

·         Chemotaxonomy – it is based chemical constituents of the plants.

1.ALGAE :

·         Simple, thalloid, autotrophic, aquatic organisms.

·         Habitats – grow in moist soil and wood.

·         Symbiotic ( Lichens) grow on other animals (sloth bear)

·         Size ranges from Unicellular colonial (volvox), Filamentous ( spirogyra) and Massive bodies (kelp)

·         Reproduce vegetatively, asexually and sexually

·         Spores are Zoospores (male) à isogamous / anisogamous; Oospores (egg).

Economic importance:

1.       Porphyra, Laminaria,  Sargassum are used as food.

2.       Marine brown algae (Algin) and red algae (Carrageen) are used as Hydrocolloids, which is a fibrous structure holds water  and used to transport seedling.

3.       Gelidium, Graularia are used to grow microbes, make ice creams and jellies.

4.       Chlorella and Spirullina are rich in proteins and used as food supplements.

Alage is divided into 3 main classes;

a)      Chlorophycease – green algae

b)      Phaeophyceae – brown algae

c)       Rhodophyceae – red algae

a)Chlorophycease (Green algae):

·         Colonial / filamentous / unicellular

·         Possess chlorophyll a & b

·         Stored with proteins / starch

·         Some store oil forms

·         Cell wall is rigid and made of inner cellulose and outer pectose

·         Vegetative reproduction is by fragmentation / spores

·         Asexual reproduction is by flagellated Zoospores

·         Sexual reproduction is by isogamous / anisogamous / oogamous

Examples : - Volvox, Spirogyra, Chlamydomonas

b)Phaeophycease (Brown algae)

·         Marine habitats – vary in size and form from simple branched to filamentous form, Kelp (100 m) possess chlorophyll a & c, carotenoid, Xanthophylls and Fucoxanthin.

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

·         They have cellulose wass with gelatinous coating of algin.

·         They are attached to substratum by Holdfast (root like), Stalk (stipe) and leaf (frond)

·         Vegetative reproduction by fragmentation

·         Asexual reproduction is by biflagellated zoospores

·         Sexual reproduction is by Isogamous / Anisogamous / Oogamous.

Examples :- Laminaria, Srgassum, Ectocarpus, Dictyota, Fucus.

c)Rhodophycease ( Red algae)

·         They have red pigment called “r-phycoerythrin”.

·         They are marine.

·         Food is stored as Floridean starch, which is similar to amylopectin and glycogen in structure.

·         Vegetative reproduction is by fragmentation.

·         Asexually by non-motile spores.

·         Sexually by non-motile gametes.

Examples : - Porphyra, Gracilaria, Gelidium.

II.BRYOPHYTES

·         They live in moist shaded areas in the hill.

·         It is known as “amphibians of plant kingdom”.

·         They occur in damp soil, humid and shaded places.

·         Plant body lacks true roots, stem, leaves, they are attached to the substratum by unicellular / multicellular Rhizoids.

·         The main plant is haploid and they produce gametes (Gametophyte – dominant).

·         The male sex organ is Antheridium (antherozoids)

·         The female sex organ is Archegonium (single egg)

·         Antherozoids are released in water come into contact with Archegonium to form Zygote.

·         Zygote develops into Sporophyte (diploid) undergoes meiosis to form haploid spores germinate to produce Gametophyte.

Economic importance:

·         Provide food for herbaceous mammals / birds.

·         Sphagnum species (mosses) provide peat, used as a fuel.

·         Due to its water holding capacity is is used as packing material for trans-shipment of living materials.

·         Mosses and Lichens form Pioneer community on bare rocks.

·         Form dense mats on soil, so reduce the impact of rain and soil erosion.

Classes:  - There are two classes à Liverworts, Mosses.

a)Liverworts :

·         Moist, shady habitats, damp soil, bark of trees and deep in the woods.

·         Plant body is Thalloid, have a tiny leaf structures.

·         Asexual reproduction is by fragmentation / form gemmae (gree, multicellular, asexual bodies) they detach from parent body and form as a new individual.

·         Sexual reproduction à form male & female sex organs sporophyte is differentiated into a foot, setae and capsule.

·         Spore germinate to form gametophyte.

Example :- Marchantia

b)Mosses :

·         Gametophyte shows two stages à Protonema (spores) and Leafy stage (Secondary protonema)

·         Attached to the soil by Rhizoids

·         Vegetative reproduction is by fragmentation / budding

·         Sexual reproduction is by antheridia and archegonia

·         Zygote develops into sporophyte and form capsule and it contains spores (haploid)

Example : - Sphagnum, Funaria

III.PTERIDOPHYTES  (first land plants):

                They are used for medical purpose, ornamental and as soil binders and first terrestrial plants.

·         They grow in cool, damp, shady places

·         Possess vascular tissues (xylem and phloem)

·         Main plant body is Sporophytes

·         The body is differentiated into true roots, stem and leaves.

·         Leaves may be small (microphylls – selaginella) or large (macrophylls – ferns) and bear sporangia and form sporophylls (leaf carrying spores).

·         Sporangia produce spores by meiosis.

·         Spore germinates to form gametophyte, called Prothallus.

·         They need water for fertilization.

·         Gametophyte bear male & female sex organs called Antheridia and Archaegonia respectively.

·         Gamete fusion results in zygote formation. Zygote develops into sporophytes (dominant phase).

·         If all the spores are similar kind, it is called Homospores.

·         Selaginella produce two kinds of spores, Macro and micro spores, hence known as Heterosporous.

·         Macro and micro spores develop into female and male gametophytes respectively.

·         Female gametophyte retained on sporophyte. It leads to the development of seed habit.

Classes: - There are four classes in Pteridophtae;

a)      Psilopsida – Ex. Psilotum

b)      Lycopsida – Ex. Selaginella

c)       Sphenopsida – Ex. Equisetum

d)      Pteropsida – Ex. Pteris

IV. GYMNOSPERMS (Naked seeds)

·         They are seed bearing plants.

·         The ovules are not enclosed in an ovary, so no fruits.

·         Tallest gymnosperm is Sequoia (red wood tree)

·         Plant body is differentiated into roots, stems and leaves

·         Roots are tap root – associated with other organisms like Pinus roots with Mycorrhizae and Cycas roots with Cyanobacteria like Nostoc and Anabaena (nitrogen fixing microbes)

·         Stem can be branched / unbranched

·         Leaves are simple / needle like – leaves show Xerophytic adaptation

·         Gymnosperms are heterosporous, produce microspores and megaspores

·         They form male cones & female cones

·         Both cones can occur on some plant / different.

·         Fertilization results in Zygote and embryo develops.

·         Ovules form seeds.

·         Gymnosperms show diplontic life cycle.

·         They show Alternation of generation.

Examples ; - Pinus, Cycas, Cedrus

V. ANGIOSPERMS (flowering plants)

·         They are flowering plants

·         Seeds are covered by fruits – live in wide range of habitats.

·         Size varies from tiny microscopic Wolfia to tall trees Eucalyptus.

·         Provide food, fodder, fuel and medicine.

·         There are two classes à Dicotyledons and Monocotyledons.

·         Male sex organ is Stamen and female is Pistil.

·         Ovules have embryo sac; it undergoes meiosis and form egg apparatus with one egg and 2 synergids, 3 antipodal cells and 2 polar nuclei.

·         Polar nuclei fuses to form secondary polar nucleus.

·         Pollen dispersal is by pollination – pollen tube grows in to stigma and style of pistil, one male gamete fuses with egg and form zygote and other male gamete fuses with secondary polar nucleus (2n) to form Primary Endosperm Nucleus (PEN - 3n).

·         Due to two fusions, it is called Double fertilization.

a)      Zygote à  Embryo

b)      PEN  à  Endosperm (and nourishes embryo)

c)       Synergids and antipodal cells à degenerate

d)      Ovules à seeds

e)      Ovary à Fruits

Life cycle patterns :

1.Haplontic life cycle:

• In haplontic life cycle, haploid individual forms haploid gamete by mitosis during gametogenesis.
• Then, this gamete (N) fuses and forms zygote that is diploid.
• This zygote undergoes meiosis to form haploid adult. Hence, adult is haploid and exhibits zygotic meiosis.
• It takes place in Spirogyra, Chlamydomonas, and Volvox.

 

2. Diplontic life cycle:

• In diplontic life cycle, diploid individual forms haploid gamete by meiosis during gametogenesis.
• Then, these gametes (N) fuse and form zygote that is diploid, which by mitosis forms diploid adult.
• Hence, adult is diploid and exhibits gametic meiosis.
• It takes place in all seed-bearing plants such as gymnosperms and angiosperms.

 

3. Haplo-diplontic cycle:

 

• Both haplontic and diplontic type of life cycle alternate with each other.
• It takes place in bryophytes and pteridophytes.