Types of Classification System:-
Artificial System of classification:-
This system used only gross superficial morphological characterizes such as habit, color, no. & shapes of leaves etc. They separated the closely related species.
Natural classification System:-
Phylogenetic classification System:-
- Given by George Bentham & Joseph Dalton Hook.
- It considers both external & internal features like anatomy, ultrastructure, embryology & phytochemistry.
- Evolutionary basis is neglected.
- It is based on evolutionary relationships among organisms.
- They use information from various sources to solve problems of classification; such information becomes more important in the absence of supporting fossil evidence.
- But, this system is not helpful in plant identification.
Types of Taxonomies:-
- It is carried out by quantitative assessment of similarity and differences in outer to make objective.
- No. & codes are assigned to all the characters & the data are then processed using a computer.
- It is based on the cytological information like numbers, structure & behavior of chromosomes during cell division specially meiosis.
- It is based on chemical constituents (enzymes, hormones, proteins, etc.) of plants.
DIVISION THALLOPHYTA [Algae]
Classification of Algae:-
- Algae are chlorophyll bearing simple, thalloid, autotrophic and largely aquatic organisms.
- Some algae form occurs on moist soil, rocks, tree trunk; some are epiphytes on animals like sloth bear and some are symbionts in lichen.
- Vegetative reproduction occurs by fragmentation.
- Asexual reproduction occurs during favourable conditions by the formation of zoospores (motile, flagellaed) or aplanospores.
- Sexual reproduction may be Isogamous (two morphologically similar gametes) for example – Spirogyra; Anisogamous (structurally dissimilar gametes) For example- Chlamydomonas) or Oogamous (motile small male gamete & non motile bigger female gamete) For example- Volvox)
- Embryonic stage is not present.
Algae are classified on the basis of pigmentations, stored food & flagellation.
The 3 main classes of algae are:-
- Chlorophyceae [Green Algae]
- Phaeophyceae [Brown algae]
- Rhodophyceae [Red Algae]
Economic importance of Algae:-
They have characteristics pigments- chlorophyll a-, b, Xanthophyll & carotens.
They have characteristic pigments – Fucoxanthin, chlorophyll-a, c, xanthophylls & carotens.
They have characteristic pigments – r – phycoerythrin along with chlorophyll –a & d.
The reserve food materials are in the form of pyrenoids (starch + protein), oil droplets.
The reserve food material are in the form of laminarin & mannitol
The reserve food material is in the form of floridean starch. [Amylopectin]
Phycocolloids are absent.
Phycocolloids are absent.
Phycocolloids are present.
2-8, equal apical
They have flagellated gametes & zoo- spores.
They don’t have any flagellated & motile structure.
Ex. – Spirogyra; Volvox, Chara, chlamydomonas.
Ex. – Laminaria and Sargassum, Fucus.
Ex. – Gelidium, Porphyra or polysiphonia.
- Algae are responsible for CO2 fixation by the process of photosynthesis.
- The algae Gelidium and Gracilaria are used to produce Agar which is used in preparation of ice- cream & jellies.
- Some protein rich algae like chlorella & spirulina are used as food supplements by sailors & space – travelers.
- Some forms of marine brown algae [Algin] & red algae [carrageenan] produce hydrocolloids which have many commercial uses.
- Marine algae are used as food [Ex.- Porphyra, laminaria & sargassum]
DIVISION:- BRYOPHYTES:- (Amphibians of plant kingdom)
LIVERWORTS:- (Marchantia, Riccia, etc.)
- It includes various Mosses & Liverworts which are non- vascular embryophytes characterized by presence of independent gametophyte & parasitic saprophytes.
- They are called amphibians of the plant kingdom because they can live in soil but are dependent on water for sexual reproduction.
- These are attached to the substratum by unicellular or multicellular rhizoids.
- The dominant phase of the plant body is the gametophyte; it is haploid and produces gametes for sexual reproduction.
- The sex organs are multicellular & have sterile jacket layer.
- The diploid zygote represents the first cell of sporophyte that undergoes mitotic division & forms the saprophytic body which is dependent on gametophyte.
- The male sex organ in bryophyte is called Anthreidium [produces biflagellate antherozoides] & the flask shaped female sex organ is called archigonium [produces single egg].
- The sporophyte at maturity bears sporangia where the spore mother cell undergoes meiosis to form haploid spores, which germinate to produce gametophyte plant body (Protonema)
- Bryophytes are broadly divided into:- Liverworts & Mosses.
MOSSES [Funaria & Sphagnum]
- The plant body (gametophyte) is dorsiventral thallus, closely appressed to the substratum, the leafy members have tiny leaf-like appendages borne on the stem like structure.
- Rhizoids are unicellular.
- Vegetative reproduction is by fragmentation or by formation of gemmae. (Green multi cellular asexual bud).
- Sex organ may be born on the same thallus or on different thalli.
- Fertilization occurs inside Archegonium & zygote develops into sporophyte which is differentiated into foot, Seta & capsule & spores are produced within capsule through meiosis which germinate to produce gametophyte.
- The dominant phase is gametophyte which occurs in two stages:-
- The protonema stage
- The erect leafy gametophyte plant
Differences between Liverworts & Mosses:-
- Rhizoids are multicellular.
- Vegetative reproduction is by fragmentation & by budding in the secondary protonema.
- Sex organs are produced in clusters at the apex of the leafy shoot. The zygote develops into a sporophyte which is differentiated into, foot, Seta & capsule. And spores are produced in capsules which germinate to produce primary protonema which later produces secondary protonema that form erect leafy plants.
- The plant body is dorsiventral thallus.
- Rhizoids are unicellular & unbranched.
- Plants bear scales.
- The sporophyte is simple & embedded in the thallus itself. It is the sporogonium where spores are formed.
- Spores germinate into gametophytic thallus.
- Mid- rib is not present in leaves.
- Plant body is leafy gametophyte with radial symmetry.
- Rhizoids are multicellular & branched.
- Scales are absent.
- The sporophyte is differentiating into foot, Seta & capsule and spores are present in the capsule.
- Spores germinate into protonema, juvenile gametophytic stage.
- Leaves have an unbranched mid- rib.
- Some mosses provide food to herbivorous plants.
- Sphagnum provides peat which has been used as fuel.
- Due to water holding capacity, species of sphagnum are used as packing material for trans – shipment of living materials.
- Some mosses are pioneer species to colonise rocks along with lichens & bring about ecological succession.
- Mosses form dense mats in the soil & prevent soil erosion.
- Marchantia has medicinal properties to cure lungs & liver infection.
Classification of Pteridophyte:-
- These are the first terrestrial plants to possess vascular tissues & called cryptogams.
- The dominant phase is sporophyte & it is differentiated into true roots, stems & leaves, all of which possess vascular tissues.
- At maturity certain leaves are modified into sporophylls & bears sporangia. Spore mother cells differentiated within sporangia undergo meiosis to produce spores.
- All the spores may be of one type (homospores) as in Dryopteris & in other ferns are of two types (heterosporous) i.e., Megospore & microspore as in Selaginella.
- The spores germinate to produce gametophyte which is multicellular, free living, thalloid & also called prothallus in ferns.
- Fusion of gametes occurs inside the Archegonia & the zygote develops into a sporophytic plant.
- Embryo formation takes place.
- Psilopsida – Ex – Psilotum
- Lycopsida – Ex – Lycopodium & Selaginella
- Sphenopsida – Ex – Equisetum
- Pteropsida – Ex – Dryopteris & Pteris
- Pteridophytes are a good source of food for animals. For example Marsilea.
- Ferns protect soil from soil erosion.
- Equisetum used in scrubbing & polishing.
- Azolla (water fern) has a symbiotic association with Anabaena, so it acts as a biofertilizer.
- Lycopodium is used in treatment of rheumatism & disorder of lungs & kidney.
- Ferns are also grown as ornamental plants.
- The gymnosperms are naked seed plants i.e., their ovules are exposed & not enclosed in ovaries.
- The sporophytic (dominant phase) plants are shrubs or moderate sized or large trees. Sequoia is the tallest tree species.
- They have a tap root system & show symbiotic association with fungi to form mycorrhiza (as in Pinus) or with nitrogen fixing cyanobacteria to form coralloid roots (as in Cycas).
- Leaves are large, pinnately compound & needle shaped.
- Vascular tissues are well developed.
- Gymnosperms are heterosporous and produce microspores in the male cones (microsporangia) & megaspores in the female cones (megasporangia).
- The plant may be monoecious (Pinus) or dioecious (Cycas).
- Spores are formed after meiosis and microspore develops into male gametophyte (pollen grain) & megaspore develops into female gametophyte within ovule.
- The pollen grains are carried by wind & deposited on the ovule. A pollen tube carries the male- gamete towards the archigorium. Fertilization occurs in archegonia & zygote develops into embryo, then slowly ovule transforms into seed.
- Seeds of pinus gerardiana (chilgoza) are used as food after roasting.
- Gymnosperms provide softwood for construction, plywood & paper – industry.
- Sawdust of conifers is used in making plastics & linoleum.
- Ephedrine an antibiotic is obtained from ephedra.
- Resin is a semi – fluid secreted by special tubes of a number of conifers.
Male Sex organs:-
- Angiosperms are seed – bearing plants or flowering plants.
- The ovules are enclosed in ovaries & hence the seeds are found within fruits.
- Vascular tissues are well developed. Xylem has vessels & phloem has sieve tubes & companion cells.
- Flower, the reproductive structure may be bisexual (monoecious) or unisexual (dioecious).
Female Sex organs:-
- Stamens are the male sex organ of a flower. Each stamen has filament & anther.
- Anther contain four microsporangia in which microspore mother cells undergo meiosis to form. 4 – microspores, each of which develops into pollen grains (Male gametophyte).
- Pistil/ Gynoecium/ Carpel is the female sex organ of a flower which has 3 parts:-
Each ovule (mega sporangia) has nucellus covered two – integuments except at the micropile end. Only 1 – megaspore mother cell in the nucellus undergo meiosis to form only 1 – functional megaspore which forms the female gametophyte (embryo sac)
An embryo sac contains egg apparatus consisting of 1- female gamete & 2 – synergids (at micropile end) and 3 – Antipodal cells (at the chalazal end) & two polar nuclei in the central cells which later fuse to form diploid secondary nucleus.
Reproduction :- (fertilization)
Classification of Angiosperms:-
- PollenGrains are brought to the surface of the stigma of the pistil during pollination.
- Each pollen grain germinates forming a pollen tube that carries 2 – male gametes to the embryo sac.
- One of the male gamete fuses with the female gamete (egg cell) to form a zygote (syngamy). And the second male gamete fuses with the diploid secondary nucleus to form triploid primary endosperm nucleus (PEN) (Triple fusion).
- Since, there are 2 fusion in an ovule during fertilization, this phenomenon is called double fertilization.
- After fertilization synergids & anti – podal cells are degenerate. Zygote develops into embryo & PEN develops into endosperm. The ovule gradually transforms into seeds & the ovary becomes the fruit.
- Angiosperms are classified based on the no. of cotyledons in their seeds, into two classes:-
- Monocotyledonae:- which have 1 cotyledon
- Dicotyledonae:- which have 2 – cotyledons.
- They contain 1 cotyledon.
- Leaves have 11 venation.
- Fibrous root system is present.
- Flowers are trimerous.
- Stomata are dump- bell shaped.
- Cambium is absent.
- Secondary growth is absent.
- Vascular bundles are scattered.
- They contain 2 cotyledons.
- Leaves have reticulate venation.
- Tap root system is present.
- Flowers are pentamerous.
- Stomata are kidney shaped.
- Cambium is present.
- They show secondary growth is stems.
- Vascular bundles are arranged in rings.
- Angiosperms are major source of food, fibres, spices & beverages.
- They also provide valuable timber & medicines.
Alternation of Generation:-
In the life – cycle of sexually reproducing plants, there is a regular alteration between the gamete producing, haploid gametophyte & the spore producing, diploid sporophyte, each producing the other.
Patterns of life cycle:-
Haplontic life cycle:-
Diplontic life cycle:-
- The dominant phase in the life cycle is the free living gametophyte.
- The diploid phase is represented only by a single celled zygote.
- Zygote undergoes meiosis to form ‘haploid spores' which form the gametophyte. For example. most of the algae like volvox, spirogyra etc.
(iii) Haplo Diplontic Life Cycle:-
- Plants showing this type of life cycles, the dominant photosynthetic phase is the diploid sporophyte .
- The haploid phase is represented by a short –lived and one or few celled gametophyte. For example:- All gymnosperms, all angiosperms & algae like focus.
- Both the sporophytic & gametophytic phases are multicellular and dominant phase in the life cycle may be gametophyte or sporophyte.
- In Bryophytes, the dominant & the independent phase is thalloid or gametophyte & it alternates with the relatively short lived multicellular sporophyte which is dependent on gametophyte.
- In Pteriodphytes, the dominant phase is represented by independent sporophytic plant body. It alternates with the short lived multicellular autotrophic & independent gametophyte. For example- Bryophytes, Pteridophytes & some algae like ectocarpus.
- These pteridophytes produce only 1 kind of spores.
- Each spore germinate into monoecious prothallus that bears both Antheridia & Archegonia.
- Ex:- Dryopteris
- These produce 2 types of spores- Micro & Megaspores.
- Microspore germinates into male gametophyte & megaspore germinates into female gametophyte.
- Ex- Selaginella, Salvinia.
- The dominant phase is gametophyte.
- Vascular tissues are absent.
- Sporophyte is dependent on gametophyte.
- True stem & leaves are not present.
- Roots are absent, rhizoids are present.
- The dominant phase is sporophyte.
- Vascular tissues are present.
- Sporophyte has independent existence.
- It has true stem & leaves.
- Roots are present.
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- Vessels or tracheids are absent in xylem.
- Phloem contains sieve cells.
- Sporophylls are aggregates to form cones.
- Ovules are exposed.
- Single fertilization.
- Seeds exposed because there is no ovary, so no fruit formation.
- Endosperm is diploid & forms before fertilization.
- Trachea is present in xylem.
- Phloem contains sieve tube & companion cells.
- Sporophylls are aggregated flower.
- Ovule are enclosed in ovary.
- Double fertilization.
- Seeds are enclosed in fruits which forms after fertilization.
- Endosperm is triploid & form after fertilization.