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Chapter 1.Reproduction in organisem
 

Chapter 1.Reproduction in organisem

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    Chapter 1.Reproduction in organisem Chapter 1.Reproduction in organisem Presentation Transcript

    • Reproduction in organism. • Introduction: • The period of birth to natural death of an organism is called life span. No individual is immortal except unicellular organism. Because it continue its life in progeny by fission.
    • Approximate life span of some organism. .
    • The continuity of life on earth is achieved by the process of reproduction.
    • • Reproduction: It is a biological process in which an organism gives rice to young ones or offspring. • Reproduction enables the continuity of species generation after generation. • Types of reproduction: • Asexual reproduction: It is the reproduction by single parent with out formation of gametes. • Sexual reproduction: It is the reproduction in which two parents of opposite sex involves with the formation and fusion of gametes.
    • Asexual reproduction. • The offspring developed by asexual reproduction are exact copy of heir parents. They are genetically identical. Hence they are termed as clones. • Asexual reproduction is common in unicellular organism. In plants and in animals having simple organisations. • Binary fission: The single cell organism of kingdom Monera and Protista reproduce by simple cell division called binary fission. The cell divides in to two half. Each half develops in to new an adult.
    • Binary fission in amoeba.
    • • Zoospores: These are motile asexual spores of algae, fungi. They use flagellum for locomotion.
    • • Bud: In yeast the cell division is unequal and small buds are produced. Initially these are attached to parent cells. Later separates and develops into new individual. • In hydra small outgrowth forms bud.
    • • Conidia: These are the asexual spores of fungus generated by mitosis. • Ex: penicillium. • In phylum Ascomycota (sac fungi)conidia develops on special stalk conidiophores.
    • • Gemmules: These are the internal buds of fresh water sponges. They resist drought, high temp, freezing, lac of oxygen etc.
    • Vegetative reproduction • Asexual reproduction in plants is termed as vegetative reproduction. • Naturally it occurs by 1. Runner. 2. Rhizome. 3. Suckers. 4. Tuber. 5. Offset. 6. Bulb etc.
    • • Runner or stolon: It is slender stem that grows horizontally to ground. Naturally it cut off and separated develops in to new individual. • Ex: strawberry.
    • • Rhizome: It is the modified underground stem. • If a rhizome is separated into pieces, each piece may be able to give rise to a new plant. • Ex: Ginger. canna
    • • Suckers: It is a basal shoot, root sprout, adventitious shoot. It grows from a bud at the base of a tree or shrub or from its roots. • Ex: Cherry. Apple.
    • • Tuber: Tubers modified plant structures that are enlarged to store nutrients. • These are short, thickened underground stem. • It bears minute scale leaves with a bud. It has the ability for developing into a new plant. • Ex: potato
    • • Offset: Offset is a small, virtually complete daughter plant that asexually produced on the mother plant. • Ex: water hyacinth.
    • • Bulb: A bulb is a short stem with fleshy leaves or leaf bases. • Ex: Onion, Garlic etc.
    • • Terror of Bengal: • Aquatic plant “Water hyacianth” ( Eichhornia) is considered as terror of Bengal. It was first introduced in India because of beautiful flower and shape of leaf.
    • • It rapidly reproduced by vegetative method offset in short period. It drains Oxygen from water that leads to death of fishes. Hence it considered as water weed.
    • Sexual reproduction • It involves the formation of male and female gametes in same individual ( bisexual) or different individual (unisexual) of opposite sex. • All organism reaches the stage of growth and maturity before they reproduce sexually. • Juvenile phase: In animals , the period of growth to attain maturity is called juvenile phase. In plants is called vegetative phase. • In angiosperms end of vegetative phase completes as soon as they start flowering.
    • • Senescent phase: The end of reproductive phase is called senescent phase or old age. After this individual dies up. flowering in plants: • In annual and biannual plants, flowering is once or twice in a year. In these plants vegetative, reproduction and senescent phase are clearly identified. Ex: Rice, wheat, marigold etc. • In some plants flowering occurs several times in particular season. • In some plants flowering occurs only once in a life time. After that plats dies up.
    • • Ex: bamboo flowering after 50 to 100 years. • Kuranji ( strobilanthus kunthiana) flowers once in 12 years.
    • Reproductive cycles in animals. • Reproduction in animals is seasonal. Birds lay eggs only in specific season. • The placental animals exhibits reproductive cycle that leads to change in ovaries and hormones level.
    • • Oestrus cycle: • It is the reproductive cycle of non primates animals like cow. dogs, rats, tigers etc. • These animals are reproductively active only in specific season. Hence these are called seasonal breeders. • Menstrual cycle: it is the reproductive cycle of primates like monkeys, apes and human these are reproductively active through out their reproductive phase. • Hence these are called continues breeders.
    • • Events in sexual reproduction: • 1. pre fertilization event: It involves the gametogenesis and gamete transfer. • 2. post fertilization event: It involves the formation of zygote and embryogenesis. • Gametogenesis: It is the process of formation of male and female haploid gametes. • Homogametes or isogametes: These morphologically similar male and female gametes. • Heterogametes: These morphologically different male and female gametes. • Anthrozoid or sperm: male gamete. • Egg or ovum: female gamete.
    • Sexuality in organisms. • Homothallic or monoecious: It is the bisexual condition in fungi, and plant. In this both male and female reproductive structure are present in single individual. • Heterothelic or diecious: It is the unisexual condition in plants. In this male and female reproductive parts are found in different flower. • Male flower – staminate bears only stamens. • Female flower – pistillate bears only pistils.
    • • Ex for monoecious plants: cucurbita. • Ex for diecious plants: papaya. date palm.
    • • Sexuality in animals: • Hermaphrodite or bisexual animals: • Animals having both male and female reproductive organs. • Ex: Tape worm. Earth worm. Sponges, leach etc.
    • • Unisexual animals: Animals having only male or female reproductive organ. Cockroach. Insects. Birds. Fishes. Amphibians. Mammals.
    • • Haploid organism: The individual having only one set of chromosomes in somatic cells. • Monera. Fungi, algae, bryophytes has haploid plant body. • Diploid organism: The individual having two set of chromosomes in somatic cells. • Pteridophytes. Gymnosperms. Angiosperms and most of animals. • In diploid organisms the gamete forms by meiosis. At the end of meiosis haploid gametes forms.
    • Transfer of gametes. • In majority of organisms male gametes are motile. Female gametes are non-motile. In few fungus and algae both male and female gametes are motile. • In algae, bryophytes and pteridophytes male gametes moves in water to reach female gamete. • The large number of male gamete are fails to reach female gamete. To compensate this loss, male gametes are produces several thousand times to female gamete.
    • • In bisexual self fertilizing plants pollen grains are easily transferred to stigma. • In unisexual and cross fertilizing plants pollination occurs by media like air, insects, bird etc.
    • • Fertilization or syngamy: It is the process of fusion of male and female gametes that result in the formation of zygote. • Parthenogenisis: It is the development of new individual with out fertilization. • Ex: honey bee. Some lizards. Turkey bird etc. • The seed less fruits are parthenocarpic fruits.
    • • External fertilization: In this fusion of male and female gamete occurs outside the body in water media. • Ex: aquatic organism like algae, fishes. Amphibians. • The dis advantages of external fertilization: 1. Organism produces large number of gametes. 2. The predators destroys eggs and offsprings. 3. The survivality rate of offspring to adult is less
    • • Internal fertilization: In this fusion of male and female gamete occurs inside the female body. • Ex: Seed plants ( gymnosperms and angiosperms). Terrestrial animals.
    • • Zygote: The fusion of haploid male and female gamete result in the formation of diploid zygote. • In fungi and algae the zygote formed has thick cell wall. It helps to resists the unfavorable condition.
    • • In haplontic ( algae like volvex, spirogyra, chlamydomanas) zygote divides by meiosis toform haploid spores. These spores develops into haploid sporophytes.
    • • In diplontic plant (Gymnosperms and angiosperms) zygote undergoes mitosis to develops into diploid dominant sporophyte.
    • • In haplo diplontic ( Bryophytes and pteridophytes) zygote undergoes mitosis to develops into diploid sporophyte.
    • • Embryogenesis: It is the process of development of embryo from zygote. The zygote undergoes division and differentiation into embryo. • Oviparous (egg laying animals): The reptiles and birds lay egg in safe environment. After incubation young one hatches out. • In oviparous embryogenesis takes place outside the body.
    • • Viviparous ( animals that gives birth to young one): most of mammals except prototheria ( egg laying mammal) are viviparous. These are placental animals. In these embryogenesis takes place inside the female body. • Because of proper embryo care and protection the chance of survivality of young one are more in viviparous than oviparous.
    • • Post fertilization changes in flower. • After zygote formation, the sepals, petals and stamens of flower falls off. • In some plants like tomato, brinjal sepals persist with fruit. • The zygote develops into embryo. • The ovule develops into seed. • The ovary develops into fruit (pericarp).
    • Sexual reproduction in flowering plants. • The reproductive structures of flower are androecium and gynoecium. • The male reproductive structure is androecium. It consists of whorl of stamens.
    • • Stamen: It has slender stalk called filament. At the tip it contains a bilobed structure called anther. • Generally anthers are bilobed that contains two theca (dithecous) separated by longitudinal grove. • The T.S of anther consists of four sided microsporangia two in each lobe. • Microsporangia develops in to pollen sac. Inside this pollen grains are present.
    • Structure of microsporangia. • Microsporangium is surrounded by 4 layers. 1. Epidermis: outer single layer of protective cells. 2. endothecium: It is a single layer of cells has the character of dehiscence. It helps to release pollen. The dehiscence character is due to their hygroscopic nature. 3. Middle layers: It is formed by 3 to 4 layers of cells. 4. Tepetum: It is the inner most layer of microsporangia. It provides nutrition to developing microspores.
    • microsporangia.
    • • Microsporengiogenesis: It is the process of formation of microspores from pollen mother cells by meiotic cell division. • The microspores formed are cluster of 4 cells called microspore tetrad. • As the anther matures, it dehydrates. The microspores dissociate and develops into pollen grains.
    • Pollen grains: • pollen grains are spherical in shape. It has two layers. Outer called exine and inner intine. • The exine is made up of an organic compound sporopollenin. • It is very hard and resistance organic compound.no one enzyme known to be degrade this one. The exine has a prominent pore called germ pore.
    • • As the pollen grain matures it contains two cells a bigger vegetative cell and smaller generative cell. • The generative cell divides mitotically in to two male gamete.
    • Gynoecium • The gynoecium is the female reproductive part of the flower. • It consist of pistil. • monocarpellary : Gynoecium consists of single pistil. • Multicarpellary: Gynoecium consists more than one pistil. • Syncarpous: Gynoecium with fused pistil. • Apocarpous: Gynoecium with free pistil.
    • Monocarpellary. • Ex:Pea. Bean.
    • Multicarpellary • -Syncarpous. • Tomato. • Cucumber
    • Apocarpous. • Ex lotus. • Vinca.
    • Pistil • Each pistil has three parts - the stigma, style and ovary. • Stigma: Stigma is the tip of pistil that serves as a landing platform for pollen grains. • Style: The style is the elongated slender part beneath the stigma. • Ovary: Ovary is the basal bulged part of the pistil.
    • • The cavity present Inside the ovary is called ovarian cavity (locule). • The megasporangia commonly called ovules arises from the placenta. • The number of ovules in an ovary may be one (wheat, paddy, mango) or many (papaya, water melon, orchids).
    • Megasporangium (Ovule) : • The ovule is a small structure attached to the placenta with stalk called funicle. • The body of the ovule fuses with funicle in the region called hilum.
    • • Each ovule has one or two protective envelopes called integuments. • Integuments encircle the ovule except at the tip. • the small opening present at tip called micropyle. • Opposite to the micropylar end the chalaza is present. • It represents the basal part of the ovule.
    • • The integument Encloses a mass of cells called the nucellus. • These cells have abundant reserve food materials. • The embryo sac or female gametophyte is located in the nucellus. • An ovule generally has a single embryo sac formed from a megaspore through reduction division.
    • Megasporogenesis • The process of formation of megaspores from the megaspore mother cell is called megasporogenesis. • Ovules generally differentiate a single megaspore mother cell (MMC) in the micropylar region of the nucellus. • The MMC undergoes meiotic division.
    • • The majority of flowering plants, one of the megaspores is functional while the other three degenerate. • Only the functional megaspore develops into the female gametophyte. • Note- the nucellus is diploid. • MMC is diploid, • the functional haploid • female gametophyte is haploid.
    • • The nucleus of the functional megaspore divides mitotically to form two nuclei. • These two moves to the opposite poles, forming the 2-nucleate embryo sac. • Two more sequential mitotic nuclear divisions result in the formation 8-nucleate stages of the embryo sac.
    • • One nucleus from each pole comes to center of embryo sac. They fuse together to form secondary nucleus. • The three nuclei at the chalazal end forms antipodal. • .
    • • The three nuclei at the micropylar end organise in to egg apparatus. • They are identified in to two synergids and an egg between them. • The angiosperm embryo sac, at maturity, though 8nucleate has 7-celled
    • Pollination • Transfer of pollen grains to the stigma of a pistil is called pollination. • Type: • Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower is called autogamy. • In these flower anthers and the stigma lie close to each other. So that selfpollination can occur
    • • chasmogamous flowers and Cleistogamous flowers : • Some plants produces two types of flowers. Ex: Viola (common pansy), Oxalis, and Commelina • Flowers with exposed anthers and stigma are called chasmogamous flower. • Flowers which do not open are called cleistogamous flowers.
    • • chasmogamous flowers and Cleistogamous flowers :
    • • Geitonogamy – Transfer of pollen grains from the anther to the stigma of the different flower of the same plant is called geotonogamy. • genetically it is similar to autogamy because the pollen grains come from the same plant.
    • • Xenogamy: Transfer of pollen grains from anther to the stigma of a different plant of same species. • Agents of Pollination : Plants use two abiotic (wind and water) and one biotic (animals) agents to achieve pollination. • Majority of plants use biotic agents for pollination. Only a small proportion of plants use abiotic agents
    • • Anemophily: The pollination occurred by the effect of wind as an agent is called anemophily. • Hydrophily: The pollination occurred by the effect of water as an agent in hydrophytes is called hydrophily. • Zoophily: The pollination occurred by the effect of animals as an agent is called zoophily.
    • • On the bases of different types of animals involved it is once again classified into, • Entamophily: The pollination occurred by the effect of insects as an agent is called entamophily. • Ornithophily: The pollination occurred by the effect of birds as an agent is called ornithophily. • Chirapterophily: The pollination occurred by the effect of bats as an agent is called chirapterophily.
    • • Anemophily: It is the pollination by wind. Small flowers are pollinated by anemophily. • These plants produces enormous amount of pollen grains. • Ex: grasses, rice, bamboo, sugar cane. etc.
    • • The anemophilous flowers are small and never coloured. • They are odourless and never produce nectar. • Pollen grains are very small, dry and light. • Stigmas are hairy and branched to trap pollen grains floating in air.
    • • Hydrophily: It is the pollination by water. Very few aquatic plants undergoes hydrophily. • When the pollination occurs below the water level is called hypohydrogamic. It seen in plants like Ceratophyllum, Hydrilla.
    • • When the pollination occurs at the water level is called epihydrogamic. It seen in plants like Vallisneria.
    • • In other aquatic plants like water hyacinth (eichhornia), water lily flower emerges out of water and pollination occurs by wind or insects.
    • • In vallisneria, the sub-merged aquatic plant, the male flowers opens at the water surface. • The released pollen grains floats on water current. • The pedicel of female flower elongates till it reaches the water surface to contact with pollen grains.
    • • Zoophily: It is the pollination by animals like insects, bees, wasp, birds, bats etc. • Majority of plants are pollinated by insects. • The entamophilous flowers has some characteristic features: • The flowers are fragrant and omits odour. Ex Jasmine. Rose. • The flowers are colour full to attract insects. • The nectar gland produces nectar to feed visiting insects. • The pollen grains are sticky or spiny. It helps to attach the body of visiting insects. • To catch pollen grains the stigma becomes sticky.
    • • Yucca plant is pollinated by moth. The moth and yucca cannot complete their life without each other. • The moth bores a hole in ovary to lay its eggs. Then it collects pollen grains from several flowers and pushes in the hallow end of stigma. • After fertilization and seed development, the larvae of moth feed on developing seeds. • The unconsumed seeds dispersed to propagation. Thus moth cannot survive without moth and yucca cannot reproduce sexually without moth.
    • • Inbreeding: The fertilization occurs within the single plant is called inbreeding • majority of plants are bisexual. The autogamy (self fertilization) and geitonogamy results in inbreeding. • The major disadvantage of self fertilization is, the progeny gets weak and causes decreased fitness in population. It is called inbreeding depression. • To avoid this plants developed many device that discourage self fertilization.
    • • Outbreeding: The fertilization occurs between two different plants of same species is called outbreeding. • The xenogamy ( cros- pollination) results in outbreeding. • The plants achieved out breeding by many mechanism. • unisexuality: The unisexual flowers are produced in same plant or different plant. • In monoecious plants with unisexual flowers, like maize, cucurbita, castor it avoids autogamy. • In dioecious plants like papaya, mulberry, it results in xenogamy.
    • • Self-sterility or incompatability: In this pollen of the flower has no fertilizing effect on stigma of the same flower. • Ex: Passiflora, potato. • Dichogamy: In this male and female sex organ matures at different times. • Ex: china rose, lady’s finger, jasmine. Custard apple. • Herkogamy: The anther and stigma are placed at different position so that pollens unable to reach stigma of same flower.
    • Artificial hybridization. • Pollinating the pollen grains of one flower to the other flower of different plants of same species is called artificial hybridization. • It is one of the major approach of crop improvement program. • In this method desired pollen grains are used for pollination. • The stigma is protected from contamination with other pollen grains. It is achieved by emasculation and bagging.
    • • Emasculation: It is the removal of anthers/stamens from flower bud before it matures. • Bagging: It is the covering of emasculated flower with butter paper to prevent contamination with other pollens.
    • Pollen pistil interaction • It is the ability of pistil to recognize the pollen of same species. It undergo post pollination event that leads to fertilization. • If wrong pollen grain (other species) is landed on stigma, pistil rejects by preventing pollen germination. • The acceptance and rejection is mediated by the chemical component of pollen grain interacting with pistil.
    • Fertilization • The fertilization in angiosperms is termed as double fertilization and triple fusion. • As the pollen grains matures usually contains one vegetative cell and two generative cell that developed into male gamete. • In some plants pollen grain sheds as two cell condition. In this, generative cell divides into two male gamete as pollen tube forms.
    • • As the pollen grain lands on stigma, it starts to germinate. • The pollen tube developed comes out of germ pore. • It grows through the tissue of stigma, style and penetrates the ovule.
    • • The entry of pollen tube in to ovule is from different place is identified into, 1. Porogamy: It is the entry of pollen tube through micropyle. 2. Chalazogamy: It is the entry of pollen tube through chalaza. 3. Misogamy: It is the entry of pollen tube through integument or funicle.
    • • As pollen tube enters the ovule, the tip ruptures inside the embryo sac releasing two male gametes.
    • • One of the male gamete fuses with egg and forms diploid zygote. • The another male gamete fuses with diploid secondary nucleus to form triploid endosperm.
    • • The fusion of two polar nuclei (to form secondary diploid nucleus) and male gamete is termed as triple fusion. • The two fusions as zygote formation and triple fusion is termed as double fertilization.
    • • Post-fertilization events. • It is the events that takes place after double fertilization. It includes, 1. Endosperm development. 2. Embryo development. 3. Maturation of ovule into seed. 4. Maturation of ovary into fruit.
    • Endosperm: • The endosperm cell formed by triple fusion under goes repeated mitotic cell division to form triploid endosperm tissue. It provides nutrition to the developing embryo. • Three different types of endosperms are reported. • Nuclear endosperm: In this endosperm cell nucleus undergoes free nuclear division. All these nuclei are pushed to the periphery forming central vacuole. • The cytokinesis results in the formation of endosperm tissue. • Ex: coconut. The vacuole is filled with fluid.
    • • Cellular endosperm: In this endosperm cellular division undergoes cytokinesis. Ex: Datura. • Helobial endosperm: In first endosperm cell division two unequal cells forms. One cell undergoes cellular division and other under goes free nuclear division. Ex : monocots. • In pea, groundnut, beans endosperm is completely consumed by developing embryo. • In some seeds like groundnut, castor endosperm persists mature seeds.
    • Embryo development: • In Dicot: The zygote divides transversely in to upper suspensor cell present at micropyle region and lower embryonal cell present at chalazal region • The suspensor cell divides and forms 7 – 10 cells called suspensor. • The upper cell of suspensor enlarges and attaches to the embryo sac.
    • • The embryonal cell divides eight cells. The lower four cells develops in to plumule and two cotyledon. • The above four cells near the suspensor develops in to hypocotyl and radicle.
    • • The fully developed embryo of dicotyledons has an embryonal axis that differentiated into plumule, two cotyledons and radicle. • The lower end of radicle (root tip) is covered with root cap. • In the beginning embryo is globular. When two cotyledons differentiates it forms heart shaped.
    • • In monocots: The zygote divides transversely in to upper suspensor cell present at micropyle region and lower embryonal cell present at chalazal region. • The embryonal cell divides into globular embryo. It forms a massive cotyledon and plumule. Plumule covers by coleoptile. • The single cotyledon is called scutellum. • At lower end of embroynal axis radicle develops. It is covered by a sheath called coleorhiza.
    • • Seed: It is the final product of sexual reproduction. It is the fertilized ovule. • Seed consists of seed coat, cotyledon and embryonal axis.
    • • The cotyledons are swollen due to storage of reserve food. • The seeds are albuminous or non-albuminous. • In albuminous seed endosperm is not completely used up by embryo. Ex: wheat, maize, castor, sunflower. • In some seeds like black pepper the nucellus also present. The residual persistant nucellus is called perisperm. • In non albuminous seed endosperm is completely used up by embryo. Ex: Pea. Ground nut.
    • • The integument of ovule develops into seed coat. • The micropyle remains as a pore in the seed coat. It facilitate the entry of oxygen and water in to seed during germination. • Seeds dry up by loosing water. The embryo enters the stage of inactivity called dormancy. As the favorable condition available it starts germination. • Fruit. • The wall of ovary develops into fruit wall called pericarp. It surrounds the seed.
    • • In apple, strawberry the thalamus develops into fruit wall. Hence these are called false fruit. • The fruits developed from unfertilized ovary are called parthenocarpic fruits. These are seedless fruits.
    • • Apomixis: The seed developed without fertilization of ovule is called apomixes. • The fruits developed from unfertilized ovule are called apomictic fruits. • The progeny of hybrid segregate their characters and not maintains hybrid character generation after generation. Hence the formers should buy hybrid seeds every year. It makes expansive. • The apomixes is done in hybrid plants to avoid the segregation of characters. The formers can use hybrid seeds to raise new crop every year.
    • • Polyembryony: The presence of more than one embryo in seed is called polyembryony. Ex: citrus fruit seeds.