Plant Kingdom PDF

 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: They separated the cl...

 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: They separated the closely related species since they were based on a few characteristics. Equal weightage to vegetative & sexual characteristics. This is not acceptable since the vegetative characters are more easily affected by environment. Carl Linnaeus These are based on natural affinities among organisms. It considers external features and internal features (ultrastructure, anatomy, embryology & phytochemistry). E.g. Classification for flowering plants given by George Bentham & Joseph Dalton Hooker. George Bentham Joseph Dalton Hooker  These are based on evolutionary relationships among the organisms. This assumes that organisms in the same taxa have a common ancestor. Numerical Taxonomy: It is based on all observable characteristics. It is carried out using computers. Number & codes are assigned to all the characters and the data are processed. Thus hundreds of characters can be equally considered. Cytotaxonomy: It is based on cytological information like chromosome number, structure, behaviour etc. Chemotaxonomy: It uses the chemical constituents of the plant. Simple, thalloid, autotrophic, chlorophyll-bearing and aquatic (fresh water & marine) organisms. They also occur in moist stones, soils & wood. Some occur in association with fungi (lichen) and animals (e.g. on sloth bear). Lichens Moss Algae On Sloth hair The form and size of algae is highly variable. Microscopic unicellular forms: E.g. Chlamydomonas. Colonial forms: E.g. Volvox. Spirogyra Ulothrix Filamentous forms: E.g. Ulothrix and Spirogyra. Chalmydomonas Volvox Vegetative reproduction: By fragmentation. Each fragment develops into a thallus. Asexual reproduction: By the production of spores. E.g. zoospores (most common). They are flagellated (motile). They germinate to give rise to new plants. Sexual reproduction: Through fusion of two gametes. Sexual reproduction is many types: Isogamous: Fusion of gametes similar in size. They may be flagellated (e.g. Chlamydomonas) or non-flagellated (non-motile, e.g. Spirogyra). Anisogamous: Fusion of two gametes dissimilar in size. E.g. Some species of Chlamydomonas. Oogamous: Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete. E.g. Volvox, Fucus. Through photosynthesis, they fix half of the total CO2 on earth and increase the level of dissolved oxygen. They are primary producers and the basis of the food cycles of all aquatic animals About 70 species of marine algae are used as food. E.g. Porphyra, Laminaria &Sargassum. Agar (from Gelidium & Gracilaria) is used to grow microbes and in ice-creams & jellies. Some marine brown & red algae produce hydrocolloids (water holding substances). E.g. algin (brown algae) & carrageen (red algae). These are used commercially. Protein-rich unicellular algae like Chlorella & Spirullina are used as food supplements by space travellers. Unicellular, colonial or filamentous. Usually grass green due to the pigments chlorophyll a & b in chloroplasts. The chloroplasts may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon- shaped in different species Most of them have one or more pyrenoids (storage bodies) located in chloroplasts. Pyrenoids contain protein besides starch. Some algae store food as oil droplets. They have rigid cell wall made of an inner cellulose layer and an outer pectose layer.  Most of them have one or more pyrenoids (storage bodies) located in chloroplasts. Pyrenoids contain protein besides starch. Some algae store food as oil droplets. They have rigid cell wall made of an inner cellulose layer and an outer pectose layer. E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara. Chlamydomonas Volvox Most of them have one or more pyrenoids (storage bodies) located in chloroplasts. Pyrenoids contain protein besides starch. Some algae store food as oil droplets. They have rigid cell wall made of an inner cellulose layer and an outer pectose layer. E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara. Ulothrix Spirogyra Chara Reproduction Vegetative reproduction: By fragmentation or by formation of different types of spores. Asexual reproduction: By flagellated zoospores produced in zoosporangia. Sexual reproduction: Isogamous, anisogamous or oogamous. They are mostly marine forms. They show great variation in size & form. They range from simple branched, filamentous forms (E.g. Ectocarpus) to profusely branched forms (e.g. kelps- 100 m in height). 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 (laminarin or mannitol). The vegetative cells have a cellulosic wall covered 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). E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus. Reproduction Vegetative reproduction: By fragmentation. Asexual reproduction: By pear- shaped biflagellate zoospores (have 2 unequal laterally attached flagella). Sexual reproduction: Isogamous, anisogamous or oogamous. Union of gametes occurs in water or within the oogonium (oogamous species). Gametes are pear-shaped (pyriform) bearing 2 laterally attached flagella. Sargassum They have red thalli due to the red pigment, r- phycoerythrin. Majority are marine especially in 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. Most of them are multicellular. Some have complex body organisation. The food is stored as floridean starch which is structurally very similar to amylopectin & glycogen. E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium. Reproduction Vegetative reproduction: By fragmentation. Asexual reproduction: By non-motile spores. Sexual reproduction: Oogamous. By non-motile gametes. It has complex post fertilisation developments. Gracilaria Gelidium  Chlorophyceae Phaeophyceae Rhodophyceae Common name Green algae Brown algae Red algae Major Chlorophyll a, c, Chlorophyll a, d, Chlorophyll a, b pigments Fucoxanthin Phycoerythrin Stored food Starch Mannitol, laminarin Floridean Starch Cell wall Cellulose Cellulose and algin Cellulose Flagellar number & 2-8, equal, apical 2, unequal, lateral Absent position of insertion Fresh water, salt Fresh water (some), Habitat water & brackish Fresh water (rare), salt salt water (most) & water & brackish water water brackish water They are 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. 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. Male sex organ (antheridium) produces biflagellate antherozoids. Female sex organ (archegonium) is flask-shaped and produces a single egg. Antherozoids are released to water and meet 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. Some mosses provide food for herbaceous mammals, birds etc. 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 are ecologically important because of their 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. Primary succession Dense mat of mosses on soil 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 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 The predominant stage of the life cycle of a moss is the gametophyte. It consists of two stages: First stage: Protonema stage Second stage: Leafy stage Protonema stage: It develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage. Leafy stage: It develops from the secondary protonema as a lateral bud. They consist 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 to a sporophyte having a foot, seta & 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.  They include horsetails and ferns. They are found in cool, damp, shady places. Some flourish well in sandy-soil conditions. Evolutionarily, they are the first terrestrial plants to possess vascular tissues (xylem & phloem). In bryophytes, the dominant phase is the gametophyte. In pteridophytes, the dominant phase (main plant body) is a sporophyte. It is differentiated into true root, stem and leaves. These organs have well-differentiated vascular tissues. The leaves in pteridophyta are small (microphylls) as in Selaginella or large (macrophylls) as in ferns. They are used for medicinal purposes. They are used as soil-binders. They are grown as ornamentals.  The sporophytes bear sporangia that are subtended Sporangium by leaf-like appendages called sporophylls Sporophylls In some cases, sporophylls form distinct compact structures called strobili or cones (E.g. Selaginella, Equisetum). Sporophyte Sporangia produce spores by meiosis in spore mother cells. The spores germinate to give inconspicuous, small, multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus Prothallus requires cool, damp, shady places to grow. Also, it needs water for fertilization. So, the spread of pteridophytes is limited and restricted to narrow geographical regions. The gametophytes (prothallus) bear male and female sex organs called antheridia and archegonia, respectively Water is needed for transfer of antherozoids (male gametes from antheridia) to the mouth of archegonium. Antherozoid fuses with the egg in the archegonium to form zygote. Zygote develops to a multicellular well- differentiated sporophyte. Most of the pteridophytes produce similar kinds of spores (homosporous plants). Others produce two kinds of spores, macro (mega) & micro spores. They are heterosporous. E.g. Selaginella & Salvinia. The megaspores & microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes are retained on the parent sporophytes for variable periods. Within female gametophytes, zygotes develop into young embryos. This event is a precursor to the seed habit. It is considered as an important step in evolution. Gymnosperms (gymnos: naked, sperma: seeds) are plants in which the ovules are not enclosed by ovary wall and remain exposed before and after fertilization. Seeds that develop post-fertilization are not covered (naked). Gymnosperm ovule Angiosperm ovule They include medium- sized trees or tall trees and shrubs. The gymnosperm, Sequoia (giant redwood) is the tallest tree species. Pinus roots with mycorrhiza The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (E.g. Pinus). In plants like Cycas, small specialized roots (coralloid roots) are associated with N2- fixing cyanobacteria. Stems are unbranched (Cycas) or branched (Pinus, Cedrus). Leaves are simple or compound. They are well-adapted to withstand extreme temperature, humidity and wind. In Cycas, the pinnate leaves persist for a few years. In conifers (Pinus, Cedrus etc.), the needle-like leaves reduce the surface area. Their thick cuticle & sunken stomata also help to reduce water loss. Gymnosperms are heterosporous. They produce haploid microspores and megaspores. Some leaves are modified into sporophylls. They are compactly and spirally arranged along an axis to form lax or strobili or cones.  Sporophylls bear sporangia in which spores are produced. Sporophylls are 2 types: Microsporophylls & Megasporophylls Cycas: Female cone Microsporophylls They are arranged to male strobili (microsporangiate). Cycas They bear microsporangia. The microspores develop into male gametophytes. It is highly reduced and confined to only a limited number of cells. This gametophyte is called a pollen grain. The pollen grains are developed within the microsporangia. Megasporophylls They are arranged to female strobili (macrosporangiate). They bear megasporangia (ovules). Megasporangium mainly consists of a body called nucellus. It is protected by envelopes. The megaspore mother cell is differentiated from a cell of the nucellus. 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 The male or female cones may be borne on the same tree (Pinus) or on different trees (Cycas). 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.  LIFE CYCLE OF GYMNOSPERMS The pollen grain released from the microsporangium are carried in air currents and meet the opening of the ovules. 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.