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3. PLANT KINGDOM - E.g. Classification for flowering plants given by George Bentham & Joseph Dalton Hooker. Phylogenetic classification systems - These are based on evolutionary relationships between the various organisms. - This assumes that organisms belonging to the same taxa have a common ancestor. Other sources to resolve the problems in classification: o Numerical Taxonomy: It is based on all observable characteristics. It is now easily carried out using computers. Number and codes are assigned to all the characters and the data are processed. Thus hundreds of characters can be considered giving equal importance. o Cytotaxonomy: It is based on cytological information like chromosome number, structure, behaviour etc. o Chemotaxonomy: It uses the chemical constituents of the plant to resolve confusions. L Artificial classification systems - These are earliest systems of classification. - They were based on vegetative characters or superficial morphological characters such as habit, colour, number and shape of leaves, etc. - Linnaeus’s artificial system of classification was based on the androecium structure. Drawbacks: - Artificial systems separated the closely related species since they were based on a few characteristics. - They gave equal weightage to vegetative and sexual characteristics. This is not acceptable since the vegetative characters are more easily affected by environment. Natural classification systems - These are based on natural affinities among organisms and considered external features, internal features (ultra structure, anatomy, embryology & phytochemistry). SA N D EE P D A LA ALGAE - Algae are simple, thalloid, autotrophic, chlorophyll☺ Agar (obtained from Gelidium & Gracilaria) is used to bearing and aquatic (fresh water & marine) organisms. grow microbes and in ice-creams and jellies. - They also occur in moist stones, soils and wood. ☺ Some marine brown & red algae produce hydrocolloids - Some of them also occur in association with fungi (water holding substances). E.g. algin (brown algae) and (lichen) and animals (e.g., on sloth bear). carrageen (red algae). These are used commercially. - The form and size of algae is highly variable. ☺ Protein-rich unicellular algae like Chlorella & Spirullina o Microscopic unicellular forms: E.g. Chlamydomonas. are used as food supplements by space travellers. o Colonial forms: E.g. Volvox Algae are classified into 3 classes: Chlorophyceae, o Filamentous forms: E.g. Ulothrix and Spirogyra. Phaeophyceae and Rhodophyceae. Reproduction: Chlorophyceae (green algae) - Vegetative reproduction: By fragmentation. Each - Unicellular, colonial or filamentous. fragment develops into a thallus. - They are usually grass green due to the pigments - Asexual reproduction: By the production of spores. E.g. chlorophyll a and b localized in chloroplasts. zoospores (most common). They are flagellated (motile) - The chloroplasts may be discoid, plate-like, reticulate, and on germination gives rise to new plants. cup-shaped, spiral or ribbon-shaped in different species. - Sexual reproduction: Through fusion of two gametes. It - Most of them have one or more pyrenoids (storage is many types: bodies) located in the chloroplasts. Pyrenoids contain o Isogamous: Fusion of gametes similar in size. They protein besides starch. may be flagellated (e.g. Chlamydomonas) or non- Some algae may store food in the form of oil droplets. flagellated (non-motile, e.g. Spirogyra). - They have a rigid cell wall made of an inner layer of o Anisogamous: Fusion of two gametes dissimilar in cellulose and an outer layer of pectose. size. E.g. Some species of Chlamydomonas. - E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara. o Oogamous: Fusion between one large, non-motile Reproduction: (static) female gamete and a smaller, motile male o Vegetative reproduction by fragmentation or by gamete. E.g. Volvox, Fucus. formation of different types of spores. Benefits of algae: o Asexual reproduction is by flagellated zoospores ☺ Through photosynthesis, they fix half of the total CO2 on produced in zoosporangia. earth and increase the level of dissolved oxygen in their o Sexual reproduction may be isogamous, anisogamous immediate environment. or oogamous. ☺ They are primary producers and form the basis of the Phaeophyceae (brown algae) food cycles of all aquatic animals. - They are found primarily in marine habitats. ☺ Many marine algae (70 species) are used as food. E.g. - They show great variation in size and form. They range Porphyra, Laminaria and Sargassum. from simple branched, filamentous forms (Ectocarpus) to profusely branched forms (e.g. kelps- 100 m in height). 1 Phaeophyceae Brown algae Chlorophyll a, c, Fucoxanthin Mannitol, laminarin Cellulose and algin Rhodophyceae Red algae Chlorophyll a, d, Phycoerythrin Floridean Starch Cellulose 2-8, equal, apical 2, unequal, lateral Absent Fresh water, salt water & brackish water Fresh water (rare), salt water & brackish water Fresh water (some), salt water (most) & brackish water LA L Chlorophyceae Green algae Chlorophyll a, b Starch Cellulose P Habitat Rhodophyceae (red algae) - They have the red pigment, r-phycoerythrin. - Majority are marine especially in the warmer areas. - They occur in both well-lighted regions close to the surface of water and at great depths in oceans where relatively little light penetrates. - The red thalli of most of the red algae are multicellular. - Some of them have complex body organisation. - The food is stored as floridean starch which is very similar to amylopectin and glycogen in structure. Reproduction: o Vegetative reproduction: By fragmentation. o Asexual reproduction: By non-motile spores. o Sexual reproduction: Oogamous. By non-motile gametes. It has complex post fertilisation developments. - E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium. A Common name Major pigments Stored food Cell wall Flagellar number & position of insertion - E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus. D - They have chlorophyll a, c, carotenoids & xanthophylls. - They vary in colour from olive green to brown depending upon the amount of a xanthophyll pigment, fucoxanthin. - Food is stored as complex carbohydrates, which may be in the form of laminarin or mannitol. - The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin. - Protoplast contains plastids, central vacuole and nucleus. - Plant body is attached to substratum by a holdfast, and has a stalk (stipe) and leaf like photosynthetic organ (frond). Reproduction: o Vegetative reproduction: By fragmentation. o Asexual reproduction: By pear-shaped biflagellate zoospores (have 2 unequal laterally attached flagella). o Sexual reproduction: Isogamous, anisogamous or oogamous. Union of gametes occurs in water or within the oogonium (oogamous species). Gametes are pearshaped (pyriform) bearing 2 laterally attached flagella. EE BRYOPHYTES SA N D - They are also called amphibians of the plant kingdom because they can live in soil but need water for sexual reproduction. - They occur in damp, humid and shaded localities. Found in moist shaded areas in the hills. - Their body is more differentiated than that of algae. It is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids. - They lack true roots, stem or leaves. They may possess root-like, leaf-like or stem-like structures. - The main plant body is haploid. It produces gametes, hence is called a gametophyte. - The sex organs in bryophytes are multicellular. - The male sex organ (antheridium) produces biflagellate antherozoids. The female sex organ (archegonium) is flask-shaped and produces a single egg. - Antherozoids are released into water where they come in contact with archegonium. An antherozoid fuses with the egg to form zygote. - Zygotes do not undergo meiosis immediately. They produce a multicellular body called a sporophyte. - Sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it. Some cells of the sporophyte undergo meiosis to produce haploid spores. These spores germinate to form gametophyte. Importance of Bryophytes: ☺ Some mosses provide food for herbaceous mammals, birds and other animals. ☺ Species of Sphagnum (a moss) provide peat. It is used as fuel. It has water holding capacity so that used as packing material for trans-shipment of living material. ☺ They have great ecological importance because of their important role in plant succession on bare rocks/soil. Mosses along with lichens decompose rocks making the substrate suitable for the growth of higher plants. ☺ Since mosses form dense mats on the soil, they can prevent soil erosion. The bryophytes are divided into liverworts and mosses. Liverworts - They grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, bark of trees and deep in the woods. - Their plant body is thalloid. E.g. Marchantia. Thallus is dorsi-ventral and closely appressed to the substrate. The leafy members have tiny leaf-like appendages in two rows on the stem-like structures. - Asexual reproduction: By fragmentation of thalli, or by the formation of gemmae (sing. gemma). Gemmae are green, multicellular, asexual buds that develop in small receptacles (gemma cups) on the thalli. The 2 gemmae are detached from the parent body and germinate to form new individuals. - Sexual reproduction: Male and female sex organs are produced on the same or different thalli. Sporophyte is differentiated into a foot, seta and capsule. After meiosis, spores are produced within the capsule. These spores germinate to form free-living gametophytes. Mosses - The predominant stage of the life cycle of a moss is the gametophyte. It consists of two stages. o Protonema stage: The first stage which develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage. o Leafy stage: The second stage which develops from the secondary protonema as a lateral bud. They consist - - - - - - SA - N D - EE P D - L - PTERIDOPHYTES They include horsetails and ferns. - The gametophytes bear male and female sex organs called antheridia and archegonia, respectively. They are found in cool, damp, shady places though some may flourish well in sandy-soil conditions. - Water is required for transfer of antherozoids (male gametes from antheridia) to the mouth of archegonium. They are used for medicinal purposes and as soil-binders. They are also frequently grown as ornamentals. - Antherozoid fuses with the egg in the archegonium to form zygote. Evolutionarily, they are the first terrestrial plants to possess vascular tissues (xylem & phloem). - Zygote produces a multicellular well-differentiated sporophyte (dominant phase of pteridophytes). In bryophytes, the dominant phase in the life cycle is the gametophytic plant body. In pteridophytes, the main - Most of the pteridophytes produce similar kinds of plant body is a sporophyte which is differentiated into spores. Such plants are called homosporous. Others true root, stem and leaves. These organs possess wellproduce two kinds of spores, macro & micro spores. differentiated vascular tissues. They are heterosporous. E.g. Selaginella & Salvinia. The leaves in pteridophyta are small (microphylls) as in - The megaspores & microspores germinate and give rise to female and male gametophytes, respectively. The Selaginella or large (macrophylls) as in ferns. female gametophytes are retained on the parent The sporophytes bear sporangia that are subtended by leaf-like appendages called sporophylls. In some cases sporophytes for variable periods. sporophylls may form distinct compact structures called - Development of the zygotes into young embryos takes strobili or cones (Selaginella, Equisetum). place within female gametophytes. This event is a precursor to the seed habit. It is considered as an Sporangia produce spores by meiosis in spore mother important step in evolution. cells. The spores germinate to give rise to inconspicuous, small, multicellular, free-living, mostly photosynthetic - The pteridophytes have 4 classes: thalloid gametophytes called prothallus. 1. Psilopsida (Psilotum) 2. Lycopsida (Selaginella, Lycopodium) Prothallus requires cool, damp, shady places to grow. 3. Sphenopsida (Equisetum) Because of this restricted requirement and the need for 4. Pteropsida (Dryopteris, Pteris, Adiantum) water for fertilization, the spread of pteridophytes is limited and restricted to narrow geographical regions. A LA - of upright, slender axes bearing spirally arranged leaves. They are attached to soil through multicellular and branched rhizoids. This stage bears the sex organs. - Vegetative reproduction: By fragmentation and budding in the secondary protonema. - Sexual reproduction: The antheridia & archegonia are produced at the apex of leafy shoots. After fertilisation, zygote develops into a sporophyte, consisting of a foot, seta and capsule. The sporophyte in mosses is more elaborate than that in liverworts. The capsule contains spores. Spores are formed after meiosis. Mosses have an elaborate mechanism of spore dispersal. - E.g. Funaria, Polytrichum and Sphagnum. GYMNOSPERMS specialized roots (coralloid roots) are associated with Gymnosperms (gymnos: naked, sperma: seeds) are plants N2- fixing cyanobacteria. in which the ovules are not enclosed by ovary wall and remain exposed before and after fertilization. Seeds that - Stems are unbranched (Cycas) or branched (Pinus, develop post-fertilization are not covered (naked). Cedrus). They include medium-sized trees or tall trees and shrubs. - Leaves are simple or compound. They are well-adapted The gymnosperm, Sequoia (giant redwood) is one of the to withstand extreme temperature, humidity and wind. tallest tree species. - In Cycas the pinnate leaves persist for a few years. In conifers, the needle-like leaves reduce the surface area. The roots are generally tap roots. Their thick cuticle and sunken stomata also help to Roots in some genera have fungal association in the form reduce water loss. of mycorrhiza (Pinus). In some others (Cycas) small Reproduction: 3 - The ovules are borne on megasporophylls which may be clustered to form the female cones. - Megaspore mother cell undergoes meiosis to form four megaspores. One of the megaspores enclosed within the Megasporangium (nucellus) develops into a multicellular female gametophyte that bears two or more archegonia. The multicellular female gametophyte is also retained within megasporangium. - Unlike bryophytes and pteridophytes, in gymnosperms the male and the female gametophytes do not have an independent free-living existence. They remain within the sporangia retained on the sporophytes. - The pollen grain is released from the microsporangium. They are carried in air currents and come in contact with the opening of the ovules borne on megasporophylls. The pollen tube carrying the male gametes grows towards archegonia in the ovules and discharges their contents near the mouth of the archegonia. - After fertilization, zygote develops into an embryo and the ovules into seeds. These seeds are not covered. L - Gymnosperms are heterosporous. They produce haploid microspores and megaspores. - The two kinds of spores are produced within sporangia that are borne on sporophylls which are arranged spirally along an axis to form lax or compact strobili or cones. strobili bearing microsporophylls & - The microsporangia are called microsporangiate (male strobili). The microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells. This reduced gametophyte is called a pollen grain. The development of pollen grains takes place within the microsporangia. - The cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate (female strobili). - The male or female cones may be borne on the same tree (Pinus) or on different trees (Cycas). - The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes and the composite structure is called an ovule. SA N D EE P D A LA ANGIOSPERMS (FLOWERING PLANTS) polar nuclei. The polar nuclei eventually fuse to produce - They are an exceptionally large group of plants occurring a diploid secondary nucleus. in wide range of habitats. They range in size from tiny, almost microscopic Wolfia to tall trees of Eucalyptus - Pollen grains are dispersed from the anthers and carried (over 100 metres). by wind or other agencies to the stigma of a pistil. This is called pollination. - In angiosperms, the pollen grains and ovules are developed in specialized structures called flowers. The - The pollen grains germinate on the stigma and the seeds are enclosed by fruits. resulting pollen tubes grow through the tissues of stigma and style and reach the ovule. - They are divided into two classes: o Dicotyledons: They have 2 cotyledons in their seeds. - The pollen tubes enter the embryo-sac where two male o Monocotyledons: They have only one cotyledon. gametes are discharged. One of the male gametes fuses with the egg cell to form a zygote (syngamy). The other - Male sex organ in a flower is the stamen. Each stamen male gamete fuses with the diploid secondary nucleus to consists of a slender filament with an anther at the tip. produce the triploid primary endosperm nucleus The anthers produce pollen grains by mieosis. (PEN). Because of the involvement of two fusions, this - Female sex organ in a flower is the pistil or the carpel. event is termed as double fertilisation, an event unique Pistil consists of an ovary enclosing one to many ovules. to angiosperms. Within ovules are present highly reduced female - The zygote develops into an embryo (with one or two gametophytes (embryo sacs). cotyledons). The PEN develops into endosperm which - The embryo-sac formation is preceded by meiosis. provides nourishment to the developing embryo. Hence, each of the cells of an embryo-sac is haploid. - Synergids & antipodals degenerate after fertilization. - Each embryo-sac has a three-celled egg apparatus (one egg cell & two synergids), three antipodal cells and two - During these events the ovules develop into seeds and the ovaries develop into fruit. PLANT LIFE CYCLES AND ALTERNATION OF GENERATIONS - In plants, both haploid and diploid cells can divide by mitosis. This leads to the formation of haploid and diploid plant bodies. - Haploid plant body produces gametes by mitosis. This plant body represents a gametophyte. - After fertilization, the zygote also divides by mitosis to produce a diploid sporophytic plant body. Haploid spores are produced by this plant body by meiosis. These in turn, divide by mitosis to form a haploid plant body once again. - Thus, during the life cycle of any sexually reproducing plant, there is an alternation of generations between gamete producing haploid gametophyte and spore producing diploid sporophyte. - However, different plant groups, as well as individuals representing them, differ in the following patterns: 1. Haplontic: In this, sporophytic generation is represented only by the one-celled zygote. There are no free-living sporophytes. Meiosis in the zygote results in 4 plant. The gametophytic phase is represented by the single to few-celled haploid gametophyte. E.g. All seedbearing plants (gymnosperms & angiosperms). 3. Haplo-diplontic: Bryophytes and pteridophytes exhibit an intermediate condition (Haplo-diplontic). Both phases are multicellular and often free-living. However, they differ in their dominant phases. MODEL QUESTIONS LA Match the names given in column I with the items in column II Column I Column II a) Adiantum Bryophyte b) Sargassum Angiosperm c) Sunflower Algae d) Riccia Pteridophyte Bryophytes are called ‘amphibians of the plant kingdom’. Justify the statement. Some features of Haplontic and Diplontic life cycles are given below. Arrange them correctly in a table. Sporophyte is a single celled zygote Meioisis occurs in Zygote Sporophyte dominant No free living Sporophyte Gametophyte dominant Meioisis occurs before zygote formation Match the following. A B a. Algae Naked seeded plants. b. Pteridophytes Amphibians of plant kingdom c. Gymnosperms Flowering plants d. Angiosperms Thalloid body, photosynthetic and mainly aquatic e. Bryophytes Independent sporophytic and gametophytic phase. Commonly called ferns. The most characteristic features of angiosperms is double fertilization a. What is double fertilization? b. Why is it called triple fusion? Identify the plant group from the given data. a. Plant body is not differentiated into root, stem and leaf b. Reproductive structures are strobili Some Pteridophytes produce two types of spores. a. Name the phenomenon b. This event is an important step in evolution. Explain. 5. 6. 7. P SA 4. N D EE 2. 3. D A 1. L the formation of haploid spores. The haploid spores divide mitotically and form the gametophyte. The dominant, photosynthetic phase in such plants is the free-living gametophyte. E.g. Algae such as Volvox, Spirogyra and some species of Chlamydomonas. 2. Diplontic: In this, the diploid sporophyte is the dominant, photosynthetic, independent phase of the SANDEEP DALAL [email protected] 5