Artificial System of Classification
Based on a few characteristics
By Carolus Linnacus based on androecium structure
Natural System of Classification
Based on natural affinities among organisms
Included external as well as internal features
eg. By George Bentham and J. D. Hooker
Phylogenetic System of Classification
Based on evolutionary relationships between the various organisms
eg. By Hutchinson
Numerical Taxonomy:
Carried out using computers based on all observable characteristics
Data processed after assigning numbers and codes to all the characters.
Advantage: Each character gets equal importance and a number of characters can be considered.
Cytotaxonomy:
Based on cytological information gives importance to chromosome number, structure and behavior
Chemotaxonomy:
Importance of Algae based on chemical constituents of the plants. At least half of the total carbon dioxide fixation on earth is carried out by them.Increase oxygen level in the environment.
Many species like Laminaria, Sargassum are used as food.
Agar obtained from Gelidium and Gracilaria is used in ice-creams and jellies.
Algan obtained from brown algae are carrageon from red algae used commercially
Chlorella and Spiraling are unicellular algae, rich in protein and used even by space travelers.
Algae divided into 3 classes:
Algae are unicellular like Chlamydomonas, colonial like Volver or filamentous like Spirogyra Are simple, thalloid, autotrophic and occur in water, seil, wood element.
Help in carbon dioxide fixation by carrying out photosynthesis and have immense economic importance.
(i) Chlorophyceae
Green algae Main pigment is chlorophyll a' and 'b'
Cell wall has an inner layer of cellulose and outer layer of pectose.
Has pyrenoids made up of starch and proteins.
e.g. Chiamydomona, Volvox, Spirogyra.
(ii) Phaeophycene
Brown algae due to main pigments chlorophyll "a", "c' and fucosanthin.
Cell wall has cellulose and lignin or gelatinous coating of algin.
Has mannitol and laminarin as reserve food material
Body divisible into hold fast, stipe and frond
e.g... Ectocarpus, Fucas, Laminaria.
(iii) Rhodophyceae
Red algae due to pigments chlorophyll a. d and phycoerythrin.
Found on the surface as well as great depths in oceans.
Cell wall as cellulose.
Reserve food material is floridean starch.
e.g. Polysiphonia, Porphyrin, Gelidium
Reproduction in Algae
Vegetative reproduction by fragmentation
Asexual Reproduction: Flagellated zoospores in Chlorophyceae
Biflagellate zoospores in Phaeophyceae By non-motile spores in Rhodophyceae.
Sexual Reproduction: Isogamous, anisogamous of oogamous in
Chlorophyceae and Phaeophyceae. By non-motile gametes in Rhodophyceae.
BRYOPHYTES:
"Amphibians of the plant kingdom Occur in damp, humid places .Lack true roots, stem or leaves.Main plant body is haploid.Economic Importance: Food for herbaceous animals.Sphagnum in form of peat is used as fuel and also used for trans-shipment
of living material as it has water holding capacity, prevents soil erosion, along with lichens are first colonizers on barren rocks Is divided into two classes:
Liverworts (thalloid body, dorsiventral, …
Marchantiny and Mosses (have two stages in gametophyte-creeping, green,
branched, filamentous protonema stage and the leafy stage having spirally ar
ranged leaves e... Funaria.
Reproduction in Bryophytes
Vegetative reproduction by fragmentation.
Asexual reproduction by gemmae formed in gemma cups.
Sexual reproduction: By fusion of antherozoids produced in antheridium and egg cell produced in archegonium. This results in formation of zygote which develops into a sporophytic structure differentiated into foot, seta and capsule. Spores produced in a capsule germinute to form free-living gametophyte.
PTERIDOPHYTES:
Main plant body is a sporophyte which is differentiated into true stem and leaves.
Leaves may be small (microsporophyll) as in Selaginella or large (macrophyll) as in ferns.
Sporangia having spores are subtended by leaf-like appendages called sporophylls. (Sporophylls may be arranged to form strobili or cones.)
In Sporangia, the spore mother cells give rise to spores after meiosis.
Spores germinate to form a haploid gametophyte structure called prothallus which is free living, small, multicellular and photosynthetic.
Prothallus bears antheridia and archegonia which bear antherozoids and egg cells respectively which on fertilization form zygote.
Zygote produces multicellular, well differentiated sporophytes.
The four classes are: Psilopsida (Psilotum), Lycopsida (Selaginella), Sphenopsida (Equisetum) and Pteropsida (Pteris).
HETEROSPORY:
Two kinds of spores Le, large (macro) and small (micro) spores are produced. eg., Selaginella and Salvinia.
SEED HABIT:
The development of zygote into young embryos takes place within the female gametophyte which is retained on the parent sporophyte. This is an important step in evolution and is found in Selaginella and Salvinia among the pteridophytes.
GYMNOSPERMS:
Have naked seeds as the ovules are not enclosed by any ovary wall and remain exposed. • Male cone has microsporophylls which bear microsporangia having microspores which develop into reduced gametophytes called pollen grain.
Female cone has megasporophylls which bear megasporangia having megaspores which are enclosed within the megasporangium (Nucellus).
One megaspore develops into a female gametophyte bearing two or more archeonies.
Pollen grains carried in air currents reach ovules, form pollen tubes which reach archegonia and release male gametes which fertilize egg cells and form zygote which produces 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: Wolf Large tree: Eucalyptus
Stamen has filament and another. Anthers bear pollen grains. Pollen grains have two male gametes
Pistil has stigma, style and ovary. Ovary has ovule in which female game tophyte (embry 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 a secondary nucleus.
Pollen grain is carried by wind, water etc. reaches to stigma and produces a pollen tube which enters the embryo sac.
Double fertilization: One male gamete fuses with egg cell to form zygote which develops into embryo,Other male gamete fuses with secondary nucleus which forms triploid primary endosperm nucleus (PEN). PEN develops into endosperm which nour ishes the developing embryo.
Ovules develop into seeds and ovaries into fruits.
Alternation of generation: Haploid gametophytic and spore producing sporo phytic generation alternate with each other in this process.
Haplontic: Gametophytic phase dominant. e... Chlamydomonas
Diplontic: Sporophytic phase dominant. eg. Angiosperms and Gymnosperms
Haplo-Diplontic: Intermediate-like stage where gametophytic and sporophytic stage partially dominate at different stages, eg., Bryophytes and Pteridophytes.
Exceptions: Ectocarpus,Polysiphonia are Haplo-diplontic algae.