Classification :

Points to Remember

 Artificial 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 Classfication

     Based on evolutionary relationships between the various organisms

     By Engler and Prantl

     Later on By Hutchinson

Numerical Taxonomy :

 Carried out using computers

 Based on all observable characteristics

  Data processed after assigning number and codes to all the characters.

Advantages : Each character gets equal importance and a number of characters can be considered.

Cytotaxonomy :

 Based on cytological informations.

 Gives importance to chromosome number, structure and behaviour.

Chemotaxonomy :

 Based on Chemical constitutents of the plants.

Algae :

 Chlorophyll bearing, simple, thalloid, autotrophic and largely aquatic organisms.

Importance of Algae :

 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, Porphyra etc. are 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 commercially as hydrocolloids.

 Chlorella and Spirullina are unicellular algae, rich in protein and used even by space travellers.

 Algae are unicellular like Chlamydomonas, colonial like Volvox or or filamentous like spirogyra and Ulothrix. Occur in water, soil, wood moist stones etc.

Algae are divided into 3 classes.

1. 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 proteins.

     Pigment and pyrenoids are located in Chloroplast.

e.g., Chlamydomonas, Volvax, Spirogyra, Ulothrix, Chara.

2. Phaeophyceae

     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 into holdfast, stipe and frond.

     e.g., Ectocarpus, Fucus, Laminaria, Dictyota, Sargassum

3. Rhodophyceae

     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., Polysiphonia, Porphyra, Gelidium,Gracilaria.

Reproduction in Algae

Vegetative reproduction : by fragmentation

Asexual   Reproduction   :   Flagellated   zoospores   in   Chlorophyceae,

Biflagellated zoospores in Phaeophycease, By non-motile spores in Rhodophyceae.

Sexual Reproduction : Isogamous, anisogamous or oogamous in chlorophyceae and Phaeophyceae.

By non-motile gametes and oogamous in Rhodophyceae.

Bryophytes :

 ‘Amphibians of plant kingdom’.

 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 and also used as packing material for trans-shipment of living material, as it has water holding capacity.

Prevents soil erosion, alongwith lichens are first colonizers on barren rock.

 Is divided into two classes Liverworts (thalloid body, dorsiventral, e.g., Marchantia) and Mosses (have two stages in gametophyte–creeping, green, branched, filamentous protonema stage and the leafy stage having spirally arranged leaves e.g., Funaria, Polytrichum and Sphagnum).

Reproduction in Bryophytes

 Vegetative reproduction by fragmentation.

 Asexual reproduction by gemmae formed in gemma cups.

 Sexual reproduction : 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 from free-living gametophyt e (Protonema). Sporophyte is not free living but attached to photosynthetic gametophyte from which derives nutrition.

Pteridophytes :

 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 sporophyte which is differentiated into true root, stem and leaves.

 Leaves may be small as in Selaginella or large as in ferms.

 Sporangia having spores are 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 gametophytic structure called prothallus

which is free living, small, unicellular and photosynthetic.

 Prothallus bears antheridia and archegonia which bear antherozoids and egg cell respectively which on fertilisation from zygote. Zygote produces

multicellular, well differentiated sporophyte.

 The four classes are : Psilopsida (Psilotum), Lycopsida (Selaginella), Sphenopsida (Equisetum) and Pteropsida (Pteris).

Heterospory : Two kinds of spores i.e., large (macro) and small (micro) 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 is precursor to seed habit and this is an important step in evolution and is found Selaginella and Salvinia among the pteridophytes.

Gymnosperms :

 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 unbranched (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 roots called coralloid root which are associated with N2 fixing cyanobacteria.

 Heterosporous–Produce haploid microspores and megaspores.

 Male cone has microsporophylls which bear microsporangia having microspores which develop into reduced gametophyte called pollengrain.

 Female cone has megasporophylls which bear megasporongia having megaspores which are enclosed within the megasporangium (Nucellus). One 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.

Angiosperms :

 Called flowering plants and have seeds enclosed in fruits.

 Divided into two classes–Dicotyledons (have two cotyledons) and Monocotyledons (have one cotyledon).

 Smallest angiosperm : 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 gametophyt e (embryo sac) develops.

 Embryo sac has 7 cells and 8 nuclei.One egg cell 2 synergids, 3 antipodals and two polar nuclei which fuse to form secondary nucleus.

 Pollen grain is carried by wind, water, insects and other agents reaches to stigma and produces pollen tube which enters embryo sac.

 Double fertilisation : One male gemate fuses with egg cell (Syngamy) to form zygote which develops into embryo.

Other male gamete fuses with secondary nucleus (triple fusion) which forms triploid primary endosperm nucleus (PEN). PEN develops into endosperm which nourishes the developing embryo.

 Ovules develop into seeds and ovaries into fruits.