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CHAPTER: 3 PLANT KINGDOM. Plant kingdom is classified into five major groups: Algae Bryophytes Pteridophytes Gymnosperms Angiosperms. ARTIFICIAL CLASSIFICATION:
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Plant kingdom is classified into five major groups: • Algae • Bryophytes • Pteridophytes • Gymnosperms • Angiosperms
ARTIFICIAL CLASSIFICATION: Based on vegetative characters or on the Androecium structure. This system was given by Linnaeus. It is not accepted as we know that often the vegetative characters are more easily affected by environment.
NATURAL CLASSIFICATION SYSTEM: Based on natural affinities among the organisms. It not only considers external features but also internal features like ultra structure, anatomy, embryology and phytochemistry. For flowering plant this type of classification is given by George Bentham and Joseph Dalton Hooker.
PHYLOGENETIC CLASSIFICATION SYSTEM: Based on evolutionary relationships between various organisms. This is acceptable. This indicates that organisms belonging to the same taxa have a common ancestor.
NUMERICAL TAXONOMY: It is now easily carried out using computers and is based on all observable characteristics. Number and codes are assigned to all the characters and the data are then processed. Every character is given equal importance and a time hundred of characters can be considered.
CYTOTAXONOMY: Based on cytological information like chromosome number, structure, behaviour. • CHEMOTAXONOMY: Based on chemical constitutions of the plant to resolve confusions. Now a day it is also used by taxonomists.
ALGAE: • Chlorophyll bearing simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. • Wide range of habitats : moist stones, soil and wood, in association with fungi (lichen) and animals (on sloth bear) • Form and size is highly variable. • Size ranges from microscopic unicellular (chlamydomonas) to conical forms like volvox. • Algae may be filamentous (Ulothrix, Spirogyra). • May be branched, plant like (Kelp).
Reproduces by vegetative, asexual and sexual methods. • Vegetative reproduction by fragmentation, asexual reproduction by production of spores (zoospores). Zoospores are flagellated and on germination give rise to new plants. • Sexual reproduction by fusion of two gametes. These gametes can be flagellated and dissimilar in size (chlamydomonas) or non-flagellated but similar in size (spirogyra).
The reproduction in which there is fusion of similar gametes is called isogamous and the reproduction in which there is fusion of two dissimilar gametes is called angiosperms. Fusion between one large non-motile female gamete and a small motile male gamete is called oogamous (Volvox, Fucus). • USES OF ALGAE: • At least a half of the total CO2 fixation on each is carried out by algae through photosynthesis. • Helpful in increasing the level of O2.
Algae are Primary producers. • Porphyra, Laminaria, Sargassum used as food • Water holding substances, algin is produced by brown algae. • Water holding substances carrageen is produced by red algae. • Agar-agar is obtained from Gelidium and Gracilaria which is used for culture of microbes and preparation of ice-creams and Jellies. • Chlorella and Spirullina (unicellular algae) used as food supplements by space travellers as they are rich in protein. Supplements by space travellers as they are rich in protein.
CLASSIFICATION OF ALGAE: Classified into three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae. • CHLOROPHYCEAE: • Members are commonly called green algae. • Plant body may be unicellular, colonial or filamentous. • Green due to pigments chlorophyll ‘a’ and ‘b’. • Pigments are localised in definite chloroplasts.
Chloroplasts may be discoid, plate like, reticulate, cup shaped, spiral or ribbon shaped. • Presence of one more storage bodies called pyrenoids located in chloroplasts. Pyrenoids contain protein besides starch. • Some algae also store food in the form of oil droplets. • Rigid cell wall, inner layer of cellulose and an outer layer of pectose.
Vegetative reproduction by fragmentation or by formation of different types of spores. • Asexual reproduction by zoospores (flagellated) produced in zoosporangia. • Sexual reproduction may be isogamous, anisogamous or oogamous. • Some green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara etc.
PHAEOPHYCEAE: • Members are commonly called brown algae. • Present primarily in marine habitat. • Great variation in size and form ranges from simple branched, filamentous forms (Ectocarpus) to profusely branched forms (Kelps). • Possess chlorophyll a, c, carotenoids and xanthophylls. • Colour vary from olive green to various shade of brown depending upon the xanthophylls pigment (fucoxanthin) • Food is stored as complex carbohydrate, may be in the form of Laminarin or mannitol.
Vegetative cells have a cellulosic wall covered on the outside by a gelatinous coating of algin. • In addition to plastids, protoplast contains a centrally located vacuole and nucleus. • The plant body is differentiated into holdfast (attached to the substratum), stipe (stalk), and frond (leaf like photosynthetic organ) Vegetative reproduction by fragmentation.
Asexual reproduction mostly by biflagellate zoospores. Zoospores are pear shaped with two unequal laterally attached flagella. • Sexual reproduction may be isogamous, anisogamous and oogamous. Union of gametes takes place in water or in oogonium. The gametes are pear shaped with two laterally attached flagella. Common brown algae are: Ectocarpus, Fucus, Dictyota, Sargassum, Laminaria etc.
RHODOPHYCEAE: • Members are commonly called red algae. • Presence of red- pigment, r-phycoerythrin. • Majority of red algae are marine with greater concentrations in the warmer area. • May be present at the regions close to the surface of water or at a great depth in oceans. • Mostly multicellular, some of them have complex body organisation.
Reserve food material is in the form of floridean starch that is very similar to amylopectin and glycogen in structure. • Vegetative reproduction by fragmentation. • Asexual reproduction by non- motile spores. • Sexual reproduction by non-motile gametes. Sexual reproduction is oogamous and accompanied by complex post fertilisation developments. • Common red algae are: Polysiphonia, Porphyra, Gracilaria, Gelidium.
BRYOPHYTES: • It includes liverworts and mosses. • Present commonly in moist shaded areas. • Bryophytes are called amphibians (can live in soil but are dependent on water for sexual reproduction) • Usually occur in damp, humid or bare rocks/soil. • Plant body is thallus like and prostrate or erect and is attached to the substratum by unicellular or multicellular rhizoids. • Absence of true roots, stem or leaves.
The main plant body is haploid and it produces gametes hence called gametophyte. • Sex organs are multicellular. • The male sex organs are antheridium that produces biflagellate antherozoids. • The female sex organ is archegonium (flask shaped) that produces a single egg. • The antherozoids are released into water and fuses with egg to form zygote. Zygote forms multicellular body called sporophyte.
The sporophyte do not detached from the gametophyte and derive nutrition from it. • Some cells of sporophyte undergo meiosis to form haploid spores. Spores further germinate to form gametophyte. • ECONOMIC IMPORTANCE OF BRYOPHYTE: • Provide food for herbaceous mammals, birds and other animals. • Species of Sphagnum (moss) provide peat and used as fuel.
Sphagnum is used as packing material for trans-shipment of living material due to its water holding capacity. • Mosses along with Lichen are of great ecological importance as they decompose rocks making it suitable for the growth of higher plants. • Mosses prevent soil erosion. • Used in grafting.
CLASSIFICATION OF BRYOPHYTES: Classified into two major groups: Liverworts and Mosses. • LIVERWORTS: • Grow in moist shady habitats such as banks of streams, marshy ground, damp soil, bark of trees, deep in the woods. • Plant body is thalloid. • The thallus is dorsiventrally flattened. • The leaf members have tiny leaf-like appendages in two rows on the stem like structures.
Asexual reproduction by fragmentation of thalli or by formation of special structure called gemmae (gemma). • Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups located on the thalli. • Gemmae detached from the parent body and germinate new individuals.
Male and female sex organs are produced either on the same or on different thalli. • The sporophyte is differentiated into foot, seta and capsule. • Spores are formed within the capsule by meiosis, and spores germinate to form gametophyte. • Common liverworts are Marchantia, Riccia etc.
MOSSES: • Most prominent stage of life cycle is gametophyte. • The first stage of gametophyte is Protonema stage that directly develops from a spore. Protonema is a creeping, green, branched and filamentous stage. • The second stage is the leaf stage that develops from the secondary Protonema as a lateral bud. It consists of upright slender axes bearing spirally arranged leaves. They are attached to the soil through multicellular and branched rhizoids.
Leaf stage bears the sex organs. • Vegetative reproductive is by fragmentation and budding in secondary Protonema. • Sexual reproduction takes place by formation and antheridia and archegonia at the apex of the leafy shoots. • Antheridia forms antherozoids and archegonia forms an egg. • Fusion of antherozoid and egg forms zygote that develops into a sporophyte, consisting of foot, seta and capsule. • Capsule contains spores that are formed after meiosis. • Common mosses are Funaria, Polytrichum, and Sphagnum etc.
PTERIDOPHYTES: • It includes horsetails and ferns. • Frequently grown as ornamentals. • First terrestrial plant to posses vascular tissues (xylem and phloem) • Found in cool, damp, shady places. • Some may flourish well in sandy-soil condition. • The main plant body is a sporophyte that is differentiated into root, stem and leaves. • The leaves may be small (microphylls - Selaginella) or large (megaphylls – in ferns)
The sporophytes bear sporangia that are subtended by leaf like appendages called sporophylls. • In some cases sporophylls forms compact structure called strobili or cones (Selaginella, Equisetum) • The sporangia produce spores by meiosis that germinates to form small, multicellular, photosynthetic gametophyte called prothallus. • Prothallus requires cool, damp, shady places to grow. • Prothallus (gametophyte) bear male and female sex organs called antheridia and archegonia.
