Current Affairs 11th Class

Habitat It is commonly known as pine with about 90 species among which six species are found in India. (N. East and N. West Himalayas) occurring in wild state. These are Pinus gerardiana (Chilgoza pine), P. Wallichiana (Blue pine or Kail), P.roxburghii (Chir pine), P.merkusii (Teenasserim pine), P.insularis (Khasi pine), and P.armandi (Armand's pine). In addition to these, 4 sps. of exotic pines, i.e., P.montana, P.laricia and P.sylvestris (Scotch pine) and P.strobus (white pine) have been introduced in India. P.excelsa are found at maximum height i.e., grow upto 3500 m above see level. Structure External structure : Pinus is an evergreen, perennial plant of xerophytic nature. Mostly the species are tall and straight. The whorled branching gives a typical conical or excurrent appearance to the plant (due to apical dominance). The plant body is sporophyte and the plants are monoecious. The plant body is differentiated into roots, stem and leaves. Root : A prominent tap root is present which does not penetrate deep into the soil. Lateral roots which develops later, grow extensively and help in anchoring the plant in the soil. Root hairs are scanty. Ectotrophic mycorrhiza i.e., symbiotic association of some fungal hyphae with the ultimate branches of roots, is of common occurrence. Stem : The stem is erect, thick, cylindrical and branched. The branching is monopodial type. The main stem is covered by scaly bark. Branches are developed from the buds present in the axil of scale leaves and appear to be in whorls. These branches develop every year and help in calculating the age of the plant.     Branches are of two types : (1) Long shoots or Branches of unlimited growth : These have apical buds, grow indefinitely in whorls each year from the buds in the axil of scale leaves. These shoots spread out horizontally and bear scale leaves on them. (2) Dwarf shoots or Branches of limited growth : These branches lack apical buds and grow for a definite or short period. They arise in the axil of scale leaves on long shoots. Leaves : The leaves are of two types i.e., dimorphic – scale leaves and foliage leaves.    Scale leaves : The scale leaves are small membranous and brown. They are present on both types of branches (i.e., long and dwarf shoots). Scale leaves are non-photosynthetic. These protect the young buds. Foliage leaves : The foliage leaves are green, needle like and are born at the tips of the dwarf shoots only. Their size and number is different in different species. The dwarf shoot with needles is called a spur. On the basis of number of needles, spur is of different types as : Monofoliar (with one needle), e.g., P. monophylla. Bifoliar (with two needles), e.g., P. merkusii and P. sylvestris. Trifoliar (with three needles), e.g. P. gerardiana and P. roxburghii. Pentafoliar (with more...

(Gk. Gymnos = naked; sperma = seed) The term gymnosperm was introduced by Theophrastus. Gymnosperm (Gk. Gymnos = naked ; sperma = seed) are the plants with exposed or naked seeds or ovules. These plants represent the most ancient group of seed plants. Gymnosperms are called fruitless phanerogames or flowering plants without ovary Robert Brown (1827) separated them from angiosperms and placed under a distinct group due to presence of unprotected ovules in them. The gymnosperms originated much earlier then angiosperms. However, most of the members of this group have now become extinct and only few living forms are known today. Distribution Plants of gymnosperms occur throughout the world. The group is presently represented by only 900 living species. Of these, about 500 species belong to 'Conifers' or cone bearing plants. Several species of conifer occur in north-west America and eastern and central China. In India several members are found in Himalayas, Podocarpus and Cupressus in the central and Larix, Tsuga, Cephalotaxus in the eastern. World's tallest gymnospermous tree is Sequoia sempervirens (368.5 ft.) in height. Largest gymnospermous tree is Sequoiadendron (13-16 meters) in diameter. The longest gymnospermous tree (in age) is Pinus longavaea (4900 years old). The smallest gymnospermous tree is Zamia pygma. Habit Living gymnosperms are mostly perennials, xerophytic, evergreen, arboreal and woody plants. They grow as woody trees, bushy shrubs or rarely as climbers (e.g., Gnetales). None of them are herbs or annuals. External features (1) The plant body is sporophyte and differentiated into root, stem and leaves. (2) The plant possess well developed tap root system. In some cases the roots are symbiotically associated with algae (e.g., Coralloid roots of Cycas) or with fungi (e.g., Mycorrhizal roots of Pinus). (3) The stem is erect, aerial, solid, woody and branched (unbranched in Cycadales) but almost tuberous in Zamia. (4) The leaves may be microphyllous or megaphyllous. (5)          In gymnosperm xylem is generally made up of tracheids but vessels have been observed in Gnetum, Ephedra and Welwitschia. (6) The primitive haplochelic type of stomata are found in Cycas, Pinus, Ginkgo, Ephedra etc. (7) Dwarfism is seen in many gymnosperms perhaps due to wind velocity. eg., Picea engelmannali (15 cm). Gymnospermous wood Manoxylic wood : The wood formed may be in one ring due to persistent cambium. Such a wood is called as monoxylic e.g., Pinus. Cambial activity is short lived, cortex and pith are broad, parenchymatous rays are broad, wood is soft and commercially useless. e.g., Cycas. Pycnoxylic wood : The wood is formed in more than one ring due to ephimeral nature of cambium. Such a wood is called as polyxylic. Cambial activity is long lived, cortex and pith are reduced, parenchymatous rays are few, wood is hard and compact, wood is commercially most important and used as good quality timber. e.g., Pinus. Reproduction Gymnosperms are heterosporous, i.e., produce two different kinds of spores – the male microspores and the female megaspores. The spores are borne inside the sporangia. The two types of sporangia are borne on more...

(Gk. Angeion = covered; sperma = seed) Introduction The angiosperms, or flowering plants, constitute the most dominant and ubiquitous vascular plants of present day flora which changed the green and yellow melancholy of the earth's vegetation by the colourful brightness and fragrance of their flower. The term angiosperm means 'enclosed seed' because the ovules or potential seeds are enclosed within a hollow ovary. In this respect they are considered most highly evolved and advanced as compared with the naked seeded gymnosperms. Characteristic features (1) Angiospermous plants grow in almost every kind of habitats. In the deserts, these plants grow, flower, shed seeds and complete their life cycle in a few weeks of rainy season. Some flowering plants like Zostera, occur in shallow seas. A small orchid even lives underground. It survives as a saprophyte on decaying organic matter because of the mycorrhizal association which helps to obtain nourishment. In rain forests, some plants grow on the branches of other plants but do not obtain water or food from them. They are called epiphytes (e.g., Vanda). (2) The angiospermous leaves show reticulate or parallel venation forming areoles. The libriform fibres are present in the xylem and the companion cells are present in the phloem. The true vessels are present in the xylem of angiosperms. (3) The angiosperms produce flowers which normally consist of 4 whorls of appandages – the two outer accessory and reproductive structure such as sepals and petals and the two inner essential parts – stamens and carpels. (4) The stamens (microsporophylls) are bilaterally symmetrical. Each stamen consists of a filament and an anther. (5) The anthers produce tectate pollen grains with exine differentiated into rod-like columellae covered by a tectum. (6) In angiosperms, the insects and animals also act as pollinating agents. For this purpose the flowers possess bright and showy petals, edible pollen and nectar. (7) The carpels (= megasporophylls) are rolled and partly sterile so that they enclose the ovules within a hollow ovary that is connected with the stigma and style. (8) The female gametophyte is highly reduced and consists of single egg cell, two synergids, three antipodals and two polar nuclei. The archegonia are absent. (9) The most characteristic feature of angiosperms is double fertilization. (i) The male gamete fuses with the egg producing diploid zygote that develops into embryo or new sporophyte. (ii) Another male gamete fuses with the polar nuclei (triple fusion) resulting in the formation of triploid endosperm. (10) After fertilization, the ovules ripens into seeds and ovary ripens into fruits. Size (1) The smallest angiosperm is Wolffia. The plant body of Wolffia consists of tiny flat oval green stem (phylloclade) having a few small roots. The plants are about 1 mm in diameter and found free floating in aquatic habitats like ponds, etc. (2) The tallest angiosperm is Eucalyptus. Their trees may attain a height upto 100 meters or more. (3) Banyan (Ficus bengalensis) tree covers a large area. It's slanting aerial branches spread in all directions. The tree spreads more...

Habitat Funaria is known as common moss or green moss or cord moss. There are 117 species of Funaria which are worldwide or cosmopolitan in distribution. 25 species have been reported from India. Most common species are Funaria hygrometrica, F.obtusa, F. attentua and F. fasicularis. Funaria grows well in recently burnt grounds rich in plant ashes (alkaline condition). Common places for its growth are moist rocks, moist walls and moist grounds. External structure (Gametophytic phase) : The main plant body of Funaria is gametophyte and is of two forms. (1) Juvenile form (creeping protonema). (2) Adult form  (leafy gametophore). Protonema is the branched filamentous portion which is produced by germination of spores. It is ephemeral or short lived. Leafy gametophore develop from buds produced on protonema and is made up of axis with spirally arranged leaves. It is 1 –3 cm in height green and is monopodially branched. The main branch of leafy gametophore bears male reproductive organs, i.e., antheridia and the side branch is female branch. Leaves : These are small, sessile, ovate with acute apex and broad base. A distinct midrib is present. On the lower portion of the leafy gametophore, there are presence of branched, multicellular rhizoids with oblique septa. Initially the rhizoids are colourless and hyaline but at maturity they become dark in colour due to dark cell walls. If rhizoids are exposed to light they become green.     Reproduction Funaria reproduces both by vegetative and sexual methods. (1) Vegetative reproduction : Vegetative reproduction takes place by fragmentation, primary protonema, secondary protonema, bulbils, gemma and apospory. In apospory some cells from any part of sporophyte separate from the parent, fall on the soil and form a protonema. Buds of leafy gametophore are produced on the protonema and give rise to a gametophyte- like plant but the cells have diploid set of chromosome (2n). In this way a gametophyte like plant is produced from diploid sporophyte without reduction division. (2) Sexual reproduction : The Funaria plants are monoecious and autoecious, i.e., male (antheridia, club shaped) and female (archegonia, flask shaped) reproductive organs are produced on the same plant but on different branches. Male organs mature first and hence Funaria plants are Protandrous. Antheridium : Main branch is male branch which is called antheridiophore. The antheridia are borne at the tip of antheridiophore. The antheridial cluster remains surrounded by a rosette of leaves called Perigonium. In between antheridia are present club shaped green multicelled sterile hair called paraphyses. An antheridium is distinguishable into stalk and the body. It has a 1-cell thick jacket. Jacket is green in the young antheridium but turn change in mature antheridium. A number of biflagellate sperms are produced by antheridium. Archegonium : Female receptacle appear bud like. It contains a number of archegonia intermixed with pointed 4-5 celled green paraphyses. The whole complex is more...

Habitat It is an unbranched filamentous green alga of stagnant fresh waters which forms floating masses (supported by bubbles of oxygen) called pond scum. A sheath of muscilage occurs on the outside. It gives a silky touch. Hence Spirogyra is also called water silk or mermaid's tresses. Structure The thallus is an unbranched and uniseriate filament where cells are arranged in a single row. In some species hold fast is present (e.g., S. fluviatilis). The cells are elongated and cylindrical. The cell wall is two layered the outer is of pectic substance and the inner of cellulose. The outer part (pectin) dissolves in water to form a muscilaginous sheath. Due to this reason Spirogyra filament's are slippery. Transverse or septum can be plane, colligate (with H-shaped piece), replicate (ring like ingrowths) and unduliseptate (undulate). The protoplast is differentiated into plasma membrane, thin layer of cytoplasm, single nucleus, one (e.g. S.sahni and S. venkataramanni) or many (16 in S.rectispora) ribbon (spiral) shaped chloroplasts (wavy margin) with pyrenoids and a large central vacuole. Nucleus occurs inside the central vacuole where it is suspended by means of cytoplasmic strands.       Reproduction Spirogyra reproduces by vegetative, asexual and sexual methods. (1) Vegetative reproduction : It takes place by fragmentation of filament. Later on, each segment gives rise to new plant. (2) Asexual reproduction : Normally asexual reproduction is absent in Spirogyra. It occurs only occasionally by the formation of akinetes, aplanospores and azygospores (Parthenospores). Akinetes : Under unfavourable conditions, the cells of the filament develop into thick walled structures, which are known as akinetes. On the onset of favourable conditions, these give rise to new plants. Their wall is made up of cellulose and pectin e.g., S. farlowi. Aplanospores : These nonmotile aplanospores are either round or oval. These later on under favourable condition give rise to the new individuals. Aplanospores are known to occur in S. aplanospora, S. articulate etc. Azygospores or Parthenospores : If there is sudden change in the environment, the gametes fail to fuse and each functions as parthenospore. (3) Sexual reproduction : The sexual reproduction in Spirogyra is called conjugation, It involves the fusion of two morphologically identical, but physiologically dissimilar gametes. The conjugation is of two types : (1) Scalariform conjugation : This is the most common and advanced type of conjugation. It involves two filaments of Spirogyra and takes place between two recently formed cells. The cells of one filament show the formation of papilla towards the other filament. It stimulates the formation of similar papilla in cells lying opposite to them. The two papillae fuse by enzymatic dissolution of the wall thus forming a conjugation canal.       The conjugation tube between the two filaments looks like a ladder, through which more...

(Gk. Pteron = father/fern; phyton = plants) The term pteridophyta was first introduced by Haeckel in (1866). The pteridophytes are flowerless, seedless, spore producing vascular plant which have successfully invaded the land. Pteridophytes represent an intermediate position between bryophytes and spermatophytes (Gymnosperm and Angiosperm). They are also called vascular cryptogams. (The term cryptogams was coined by Linnaeus (1737) which means plants without seeds). The group has a long fossil history. Pteridophytes flourished well during devonian, mississipian and pensylvanian periods of late paleozoic age. This period can be well recognised as "age of pteridophyta". Habitat The plants of pteridophytes are mostly terrestrial. They prefer shady habitats. Some species of Selaginella and Adiantum are xerophytes. A fern, Acrostichum aureum is a halophyte. Some species e.g., Selaginella oregana, Psilotum flacidum, Lycopodium squarrosum and ferns like Asplenium nidus, Pleopeltis sp. are epiphytes. Marsilea occurs as a terrestrial, amphibious as well as an aquatic plant. There are true aquatic ferns like Salvinia (Salvinia is root less pteridophyte), Azolla and Ceratopteris. Sporophytic plant body (1) The main independent plant body of pteridophytes is sporophyte. It is differentiated into true roots, true stem and true leaves. (2) The primary root is short lived. It is replaced by adventitious roots. The root has a permanent growing apex. (3) The stems are usually herbaceous (except in some woody ferns) and branched monopodially or dichotomously. (4) The leaves may be small microphyllous (e.g., Lycopodium, Equisetum) or large macrophyllous (e.g., Pteridium, Pteris and other ferns). (5) All the vegetative parts possess vascular tissues (i.e., xylem and phloem) organized in definite groups or steles. Spore producing organs The plants of pteridophytes are sporophytes. They reproduce asexually by forming spores in sporangia. They are homosporous but a few plants are heterosporous also e.g., Isoetes, Selaginella, Marsilea, Regnellidium, Pilularia, Azolla and Salvinia. In Selaginella the sporangia are borne in relation to sporophylls which constitute a strobilus. In Equisetum they are borne on sporangiophores which constitute a cone. In ferns the sporangia are borne in sori on the sporophylls. The sori are of three types : (1) Simple sorus : Here all the sporangia mature at the same time. (2) Gradate sorus : Here the oldest sporangium lies in the centre and the sporangia on either side show successively younger stages. (3) Mixed sorus : It shows mixed arrangement of younger and older sporangia. In Marsilea, Azolla, Salvinia etc. the sori are present in a box like structure called sporocarp. The sorus may be naked or covered by an inducium. The inducia may be true or false. Sporangium The sporangia are generally stalked structures. Each sporangium is distinguishable into a jacket enclosing a mass of sporogenous tissue. The sporangial jacket may be 2-4 layered. The innermost wall layer is the tapetum. No tapetum is formed in Psilotum and Tmesipteris. It is a nutritive layer which degenerates at maturity of the sporangium. The sporangial jacket in some ferns shows distinctions of annulus and stomium. On the basis of development, the sporangia have been classified by Goebel, more...

(Gk. Bryon = moss; phyton = plants) Bryophyta includes the simplest and primitive land plants. Which are characterised by the persence of independent gametophyte and parasitic sporophyte. The term bryophyta was coined by Braun (1864) but bryophytes were delimited in its present form by Schimper (1879). It occupies a position intermediate between algae and pteridophyta. Due to peculiar type of their habitats, they are regarded as 'the amphibians of the plant kingdom'. The science connected with the study of bryophytes called bryology. Habitats Bryophytes usually grow in moist and shady places. The plants grow densely together and form green carpets or mats on damp soil, rock, walls, barks of trees and on decaying logs in forests, especially during the rainy season. Specialized habitats : Some bryophytes grow in diverse habitats such as – aquatic (e.g., Riccia fluitans, Ricciocarpus natans, Riella), epiphytes (e.g., Dendroceros, Radula protensa and many mosses), saprophytes (e.g., Buxbaumia aphylla, Cryptothallus mirabilis), and in dry habitats such as dry heaths (e.g., Polytrichum juniperinum), deserts (e.g., Tortula desertorum) and dry rocks (e.g., Porella platyphylla). Gametophytic plant body (1) The life cycle of bryophytes consists of two distinct phases – the gametophytic phase and the sporophytic phase. The haploid gametophyte is dominant, long lived, green and independent whereas the diploid sporophyte is short lived and dependent upon the gametophyte. The two phases are morphologically distinct. (2) The plants are small, range from few millimetres (e.g., Zoopsis) to 30–40 centimetres. The tallest species may reach upto 70 cm in length (e.g., Dawsonia). (3) The gametophytes are either thalloid (i.e., not differentiated into true roots, true stem and true leaves) or leafy shoot having stem-like central axis and leaf-like appendages. (4) The roots are completely absent and they are replaced by unicellular or multicellular thread like rhizoids. In some higher forms the multicellular rhizoids form cords. (5) The vascular tissue (i.e., xylem and phloem) are completely absent. Reproduction (1) Vegetative reproduction : The bryophytes reproduce vegetatively by following methods : Death and Decay : Most of these plants reproduce vegetatively by gradual death and decay of the older part of the plant body. Adventitious branches : Many plants like Riccia fluitans, Reboulia, Asterella, Pellia etc. reproduce by adventitious branches. They separate and produce new plants. Tubers : Several species of Riccia, Anthoceros, Sewardiella, Asterella etc. produce tubers which give rise to new plants on the arrival of favourable conditions. Gemmae : Several members, reproduce vegetatively by forming multicelled gemmae. In Marchantia, Lunularia, the gemmae are produced in gemma cups. Gemmae are also produced on the thallus of Anthoceros. Several mosses also produce gemmae on the 'leaves' (Bryum), or axis or rhizoids or on the protonema (Funaria). Primary protonema : The mosses generally reproduce vegetatively by breaking of the primary protonema. New gametophores now arise from the buds differentiated on it. Secondary protonema : In several mossess a secondary protonema may arise from the rhizoids or primary protonema or even from the injured sporophyte. It may produce buds which give rise to new more...

(Gk. Phycos = alga or sea weed) The branch of botany dealing with the study of algae is called as phycology or algology. They are simple, thallose, autotrophic non-vascular plants having unicelled sex organs and no embryo formation. In Whittaker's classification, algae are grouped in three kingdom – Monera (blue green algae), Protista (dinoflagellates, diatoms, euglenoids) and Plantae (green algae, red algae and brown algae). According to Fritsch, (1935) the designation alga must include all holophytic organisms, as well as their numerous colourless derivatives, that fail to reach the level of differentiation characteristic of archegoniatae plants. Occurrence : The algae occur in a variety of habitats which are summarised here under : Fresh water forms : They occurs in rivers, ponds, pools, lakes and ditches. Those forms which remain attached to bottom soil are called as epipelic. Several forms remain attached to bottom or at the bank or to submerged objects. They are described as benthos. Many forms remain attached to rocks or stones. They are described as epilithic or lithophytic. Marine forms : Most of the members of brown algae, red algae some green and blue-green algae occur in sea. While some occur as phytoplanktons and benthos, others occur as lithophytes. The giant forms like Macrocystis (60 meters) and Nereocystis (50 meters) are also marine. Terrestrial forms : Several members of green and blue-green algae and a few others occur on damps soil. While forms like Oscillatoria and Nostoc occur on alkaline and calcareous soil, Fritschiella grown on acidic soil. Xanthophyceae members like Vaucheria and Botrydium growing on damp shady soil or on shady walls, are often described as Sapophytes. Specialized habitats Cryophytes : Plants growing on snow or ice are called as cryophytes. Different algal forms produce a specific colour effect while growing as cryophyte e.g., yellow-green by Chlamydomonas yellowstonensis, red by C. nivalis, black by Scotiella nivalis and purple-brown by Ancylonema nordenskioldii. Thermophytes : Plants growing in hot water are called as thermophytes. Some blue-green algae grow in hot water springs at about 70°C e.g., Oscillatoria brevis. Epiphytes : Several algal forms grow on other plants (algae, angiosperms) as epiphytes. e.g., Oedogonium, Cladophora, Vaucheria etc. Endophytes : Some blue-green algae grows as endophytes inside other plants e.g., Anabaena growing inside the leaf of Azolla (fern), Nostoc inside the thallus of Anthoceros (hornwort) and Anabaena, Nostoc, Oscillatoria inside the coralloid roots of Cycas. Epizoic : Algae growing on the bodies of animals are described as epizoic. e.g., Cladophora crispata grows on snail shell, Characium grows on the antennae of mosquito larvae, Cyanoderma (red alga) and Trichophilus (green alga) are grow on scales of sloth. Endozoic : Algae growing inside the body of animals. e.g., Chlorella grow with in the tissue of Hydra. Some blue-green algae also grow in the respiratory tracts of animals. The blue-green algae which grow endozoically inside the protozoans are called as cyanellae. Symbiotic forms : Some algae like Chlorella, Nostoc etc. growing in symbiotic relationship with members of Ascomycetes and Basidiomycetes (Fungi) constitute the more...

The plant body of true fungi (Eumycota) is thallus. It may be non-mycelial or mycelial. The non-mycelial forms are unicellular, however, they may form a pseudomycelium by budding. In mycelial forms, the plant body is made up of thread like structures called hyphae (sing. hypha). The mycelium may be aseptate (non-septate) or septate. When non-septate and multinucleate, the mycelium is described as coenocytic. In lower fungi the mycelium is non-septate e.g., Phycomycetes. In higher forms it is septate e.g., Ascomycetes, Basidiomycetes and Deuteromycetes. In some forms the plant body is unicelled at one stage and mycelial at the other. Their organization is sometimes described as dimorphic. When the entire mycelium is converted into reproductive structure, the thallus is described as holocarpic. However, if only a part of it becomes reproductive, the thallus is called as eucarpic.

In higher forms the mycelium gets organised into loosely or compactly woven structure which looks like a tissue called plectenchyma. It is of two types : Prosenchyma : It comprises loosely woven hyphae lying almost parallel to each other. Pseudoparenchyma : If the hyphae are closely interwoven, looking like parenchyma in a cross-section, it is called as pseudoparenchyma. In addition to above, the fungal mycelium may form some specialized structures as under : Rhizomorphs : It is a 'root or string-like' elongated structure of closely packed and interwoven hyphae. The rhizomorphs may have a compact growing point. Sclerotia : Here the hyphae gets interwoven forming pseudoparenchyma with external hyphae becoming thickened to save the inner ones from desiccation. They persist for several years. Stroma : It is thick mattress of compact hyphae associated with the fruiting bodies.


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