Chapter-3
Plant Kingdom
Points to Remember
Classification :
- Artifical System of Classification
- By Carolus Linnaeus, based on androecium structure and vegetative characters.
- Natural System of Classification
- Based on natural affinities among organisms
- Included external as well as internal features.
- By Geroge Bentham and J.D. Hooker.
- Phylogenetic System of Classification
- Based on evolutionary relationships between the various organisms
- By Engler and Prantl
- Later on By Hutchinson
- Carried out using computers
- Based on all observable characterisitics
- Data processed after assigning number and codes to all the characters.
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Advantages : Each character gets equal importance and a number of character can be comsiderd.
- Based on cytological informations.
- Gives importance to chromosome number, structure and behaviour.
- Based on Chemical constituents of the plants.
- Chlorophyll bearing, simple, thalloid, autorophic and largely aquatic organisms.
- Help in carbon dioxide fixation by carrying out photosynthesis and have immense economic importance.
- At least half of the total carbon dioxide fixation on earth carried out by them.
- Increases dissolved oxygen level in their environment.
- Many species like Laminaria, Sargassum, Prophyra etc. used as food.
- Agar obtained from Gelidium and Gracilaria which is used in ice-creams and jellies and to grow microbes.
- Algin obtained from brown algae and carrageen from red algae used commerically as hydrocolloids.
- Chlorella and Spirullina are unicellular algae, rich in protein and used even by space travellrs.
- Algae are unicellular like Chlamydomonas, colonial like Volvox or filamentous like Spirogyra and Ulothrix. Occur in water, soil, wood moist stones etc.
Algae are divided into 3 classes.
(i) Chlorophyceae- Green algae, Main pigment is chlorophyll 'a' and 'b'.
- Cell wall has inner layer of cellulose and outer layer of pectose.
- Has pyrenoids made up of starch and protenis.
- Pigment and pyrenoids are located in Chloroplast.
- e.g., Chlamydomonas, Volvox, Spirogyra. Ulothrix, Chara.
- Brown algae are brown coloured due to main pigments chlorophyll 'a', 'c' and fucoxanthin (xanthophyll)
- Cell wall has cellulose with gelantionous coating of algin.
- Has mannitol and laminarin (complex carbohydrate) as reserve food material.
- Body divisible inot holdfast, stipe and frond.
- e.g., Ecotocarpus, Fucus, Laminaria, Dictyota, Sargassum
- Red algae are red coloured due to pigments chlorophyll 'a', 'd' and r-phycoerythrin.
- Found on surface as well great depths in oceans.
- Cell wall has cellulose.
- Reserve food material is floridean starch.
- e.g., Ploysiphonia, Prophyra, Gelidium, Gracilaria.
(ii) Phaeophyceae
(iii) Rhodophyceae
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Vegetative Reproduction : by fragmentation
Asexual Reproduction : Flagellated zoospores in Chlorophyceae, Biflagellated zoospores in Phaeophyceae, By non-motil spores in Rhodophyceae.
Sexual Reproduction : Isogomous, anisogamous or oogamous in Chlorophyceae and Phaeophyceae.
By non-motile gametes and oogamous in Rhodophyceae.
- 'Amphibians of plant kingdoms'.
- Occur in damp, humid and shaded places.
- Lack true roots, stem or leaves.
- Main plant body is haploid and thallus like (prostrate or erect)
- Economic Importance : Food for herbaceous animals.
Sphagnum in from of peat is used as fuel an also used as packing material for trans-shipment of living material, as it has water holding capacity. - Is divided into two classes Liverworts (thalloid body, dorsivental, e.g., Marchantia)) and Mosses (have two stages in gametophyte-creeping, green, branched, filamentous Protonema stage and leafy stage having spirally arranged leaves e.g., Funaria, Polytrichum and Sphagnum ).
- Vegetative reproductionn by fragmentation.
- Asexual reproductionn by gemmae formed in gemma cups.
- Sexual reproductionn : Main plant body is haploid, produces gametes and so called Gametophyte. By fusion of antherozoids produced in antheridium and egg cell produced in archegonium, results in formation of zygote which develops into sporophytic structure differentiated into foot, seta and capsule. Spores produced in a capsule germinate to form free-living gametophyte (Protonema). Sporophyte is not free living but attached to photosynthesis gametophyte form which it derives nutrition.
- First terrestrial plants.
- Prefer cool, damp and shady places to grow.
- Grown as ornamentals.
- Used for medicinal purpose, as soil binder.
- Main plant body is sporophytic which is differentiated inot true root, stem and leaves.
- Leaves may be small as in Selaginella or large as in ferms.
- Sporangia having spores ar subtended by leaf-like appendages called sporophylls. ( Sporphylls may be arranged to form strobili or cones. )
- In Sporangia, the spore mother cells give to spores after meiosis.
- Spores germinate to form haploid gametophyte structure called prothallus which is free living, small, unicellular and photosynthetic.
- Prothallus bears antheridia and archegonium which bear antherozoids and egg cell repectively which on fertilisation form zygote. Zygote produces multicellular, well differentiated sporophyte.
- The four classes are : Psilopsida (Psilotum), Lycopsida (Selaginella), Sphenopsida (Equisetum) and Pteridophytes (Pteris).
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Heterospory : Two kinds of spores i.e, (macro) amd small (micor) spores are produced. e.g., Selaginella and Salvinia.
Seed Habit : The development of zygote into young embryos takes place within the female gametophyte which is retained on parent sporophyte. This event in precursor to seed habit and this is an important step in evolution and is found Selaginella and Salvinia among the pteridophytes.
- Have naked seeds as the ovules are not enclosed by any ovary wall and remain exposed.
- Includes shrubs and trees (medium and tall sized).
- Have generally tap roots, stem may be unbrached (Cycas) or branched (Pinus, Cedrus), leaves-needle like (Pinus) and pinnate (Cycas).
- Roots of Pinus have fungal association in the form of mycorrhiza.
- Cycas have small specialized toots called coralliod root which are associated with N2 fixing cyanobacteria
- Heterosporous- Produce haploid microspores and megaspores.
- Male cone has microsporophylls which bear megasporongia having microscopic which develop inot reduced gametophyte called pollengrain.
- Female cone has megasporophylls which bear megasporongia having megaspores which are enclosed within the megaspore develops into female gametophyte bearing two or more archegonia.
- Pollen grains carried in air currents reach ovules, form pollen tube which reach archegonia and release male gametes which fertilise egg cell and form zygote which produce embryos. Ovules develop into seeds which are not covered.
- Called flowering plants and have seeds enclosed in fruits.
- Divided into classes-Dicotyledons (have two cotyledons) and Monocotyledons (have one cotyledon).
- Smallest angiosperms : Wolfia
- Large tree : Eucalyptus (Over 100 meters)
- Stamen has filament and anther. Anthers bear pollen grains. Pollen grains have two male gametes.
- Pistil has stigma, style and ovary. Ovary has ovule in which female gametophyte (embryo sac) develops.
- Embryo sac has 7 cells and 8 nuclei. One egg 2 synergids, 3 antipodals and two polar nuclei which fuse to form secondary nucleus.
- Pollen grain is carried by wind, water, insects and othe agents reaches to stigma and produces pollen tube which enters embroys sac.
- Double fertilisation : One male gemate fuses with egg cell (Syngamy) to form zygote which develops into embryo.
- Ovules develop into seeds and ovaries into fruits.
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Other male gamete fuses with secondary nucleus (triple fusion) which forms triploid primary endosperm nucleus (PEN). PEN develops into endosperm which nourishes the develping embryo.
