Transcript File
PLANT KINGDOM ALGAE Algae are chlorophyll bearing, simple autotrophic aquatic organisms. Occurrence Moist stones, soils & wood or in association with fungi & animals. Form & size Microscopic unicellular forms -Chlamydomonas Colonial forms -Volvox Filamentous forms-Ulothrix,spirogyra Massive forms-Kelps Reproduction 1.Vegetative reproduction – by fragmentation. 2.Asexual reproduction – by production of spores called zoospores. 3.Sexual reproduction – by fusion of gametes. a.Isogamous – gametes are similar in size.eg:Chlamydomonas,Spirogyra b.Anisogamous – gametes are dissimilar in size. eg:Some species of chlamydomonas. c.oogamous-One large,static gamete(female) & other small motile gamete(male). Significance 1.Increases the level of oxygen in the environment, 2.Many species are used as food.eg:sargassum,chlorella,spiruillina. 3.Agar obtained from Gelidium & Gracilaria in used in the preparation of icecreams & jellies. 4.Algin(brown algae) & carrageen(red algae) are used commercially as hydrocolloids. Class Chlorophy ceae (Green algae) Major pigments Stored food Cell wall Flagellar Habitat Position, Position of insertion Chlorophyll a&b Starch Cellulose 2-8,equal, Apical Fresh wa ter ,brac kish & Salt Mannitol, Laminarin Cellulose & algin 2,unequal lateral cellulose Absent Phaeophy Chlorophyll ceae(Brow a & c, n Algae) Fucoxanthin Rhodophy ceae (Red algae) Chlorophyll Floridean a & d, starch Phycoerythri n “ “ Asexual reproduction By vegetative reproduction-fragmentation & budding. By the formation of specialised structures called Gemmae.Gemmae are green, multicellular,asexual buds which develop in small receptacles called gemma cups located on the thalli.The gemmae detaches from the plant body & germinate to form new individuals. Sexual reproduction The main plant body of bryophyte is called gametophyte which produces gametes. The male sex organ is called antheridium & female sex organ is called archegonium. The biflagellate antherozoids produced from antheridium is released into water & comes in contact with archegonium. The antherozoid fuses with egg forming zygote. Zygote develops into a multicellular body called sporophyte which produces spores. Spores germinate to produce plant body. Significance 1.Species of sphagnum provide peat which is used as hydrocolloid. 2.Provide food for herbaceous mammals, birds & other animals. 3.They decompose rocks making the substrate suitable for the growth of higher plants. 4.Prevent soil erosion. 5.Mosses along with lichens are the first to colonize rocks & hence of great ecological importance. Bryophytes are divided into liverworts & mosses. 1.Liverworts (Marchantia) The thallus is dorsiventral & closely appresed to the substrate,they have leaf like appendages in two rows on the stem like structures. 2.Mosses (Funaria,Polytrichum,Sphagnum) Life cycle has mainly two stages – stage 1- Protenema Creeping green branched stage which directly develops from the spore. stage 2 – leafy stage Develops from protonema as a bud.They consist of slender axes bearing spirally arranged leaves,attached to the soil through rhizoids.This stage bears sex organs. Pteridophytes These are first terrestrial plants to possess vascular tissues- xylem & phloem.Usually grown as ornamentals.Seeds were first seen. Occurrence Generally found in cool,damp, shady places. Form The main plant body called sporophyte is differentiated into true root ,stem & leaves. Reproduction The sporophyte possess leaf-like structures called sporophyll which bear sporangia. Sporangia produce spores by meiosis. Spores germinate to photosynyhetic thalloid gametophytes called Prothallus. Prothallus bears antheridia & archegonia. Fusion of gametes results in a zygote. Zygote develops into a well differentiated plant body. Based on the size of spores, there are two types of reproduction 1.Homosporous reproduction- spores are of similar kinds.eg:Most of the pteridophytes. 2.Heterosporous reproduction-spores are of dissimilar size- megaspores & microspores. Eg:Selaginella,Salvinia Gymnosperms Gymnosperms are plants in which the seeds are naked. gymnos-naked & sperma-seeds. Occurrence & form They are well adapted to extremes of temperature,humidity & wind & therefore is widely distributed.Gymnosperms include medium-sized trees or tall trees & shrubs.Sequoia is one of the tallest tree species.Roots in some are in association with fungus in the form of mycorrhiza(pinus) while collaroid roots are associated with nitrogen fixing bacteria(cycas).Leaves are simple or compound. Reproduction Gymnosperms are heterosporous producing microspores & megaspores. The spores are arranged spirally along a axis to form lax or compact strobili or cones. The strobili bearing microspore is called microsporangiate or male strobili & strobili bearing megaspore is called megasporangiate or female strobili. The microspore develops into pollengrain & megaspore into ovule. In gymnosperms the gametophytes donot have a free existence as in bryophytes & pteridophytes. Fusion of pollen & ovule results in zygote. Zygote develops into embryo & ovule into seeds. Angiosperms Angiosperms are the flowering plants where the pollengrains & ovules are developed in specialised structures called flowers. Occurrence & form They are exceptionally large group of plants occuring in wide range of habitats.They range in size from tiny almost microscopic to tall trees. Angiosperms are divided into two classes. Dicotyledons - characterised by having two cotyledons. Monocotyledons – have only one cotyledon. Reproduction The male sex organ in a flower is stamen & female sex organ is pistill. Ovary in the pistill encloses ovules. Ovules carry embryo sac which has a three celled apparatus- 1egg cell & 2 synergids,three antipodal cells & 2 polar nuclei.The polar nuclei fuses to form a secondary nucleus. By pollination, pollen grains are carried to the stigma of the pistill. Pollen tube develops,enters the embryo sac where two male gametes are discharged. One of the male gamete fuses with egg forming zygote,other fuses with secondary nucleus producing PEN(primary endosperm nucleus) which is triploid.This is called double fertilization. Zygote develops into embryo & PEN into endosperm which provides nourishment to the developing embryo.