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Reproduction in organisms, Class XII

  1. Reproduction in Organisms Part-1 Presented by: Shashank Tripathi PGT Biology BNS English School, Naria, BHU, Varanasi
  2. Life Span  The period from birth to the natural death of an organism is called its life span.  Life span of an organism may be few minutes to several thousand years.
  3. Phases of Life: Juvenile/Vegetative Phase Reproductive Phase Ageing/Senescence Phase Death Phase Life of an organisms has following 4 phases-
  4. What is Reproduction???  Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parents".  Reproduction is a fundamental feature of living organisms which involves the transmission of genetic material from one generation to the next ensuring the survival of species over long periods of time.
  5. Types of Reproduction: Reproduction Asexual Reproduction Sexual Reproduction
  6. Asexual Reproduction:  Asexual reproduction is a type of reproduction which does not involve the fusion of gametes or change in the number of chromosomes.  The offspring that arise by asexual reproduction from a single cell or from a multicellular organism inherit the genes of that parent.  Organisms produced are referred as genetically ‘clone’. Benefits of Asexual Reproduction
  7. Mode of Asexual Reproduction: Asexual Reproduction Fission E.g., Amoeba Binary Fission E.g., Amoeba Multiple Fisssion E.g., Plasmodium Budding E.g., Hydra, Sycon External E.g., Hydra Internal E.g., Sycon Regeneration E.g., Planaria Fragmentation E.g., Spirogyra Sporulation E.g., Rhizopus Vegetative Propagation
  8. Fission:  Fission can be simply called as break down.  It is a primitive type of reproduction.  During the fission and organism just divides itself a-mitotically or mitotically in two almost equal halves giving rise two off-springs.  After the processes the parent cell loses its identity.  On the basis of axis of division, fission can be- Transverse Fission Longitudinal Fission  On the basis of number of off-springs produced, fission can be- Binary Multiple
  9. Binary Fission:  When an organism produces on two organisms after fission.s
  10. Teransverse & Longitudinal Binary fission: Transverse binary fission in Paramecium Longitudinal binary fission in Euglena
  11. Multiple fission:  When an organism produces more than two cells after fission.  Here the nucleus of the organism replicates first and then the cytokinesis occurs . at one time more than two daughter cells are produced.  It take place in Plasmodium.
  12. Budding: Budding Exogenous or External Endogenous or Internal Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or protuberance or bud due to cell division at one particular site.
  13. Exogenous or External Budding: Budding in Yeast Budding in Hydra
  14. Endogenous or Internal Budding:  Such type of budding is generally common in Sponges like Sycon & Spongilla  Here the budding take place inside the body of organism.  Such type of buds are called Gemmules and can be defined as tough coated dormant coated clusters of embryonic cells. Gemmules of Spongilla and Ephydatia
  15. Differences between Fission and Budding: Fission Budding • No Buds or external outgrowths formed • Buds or external outgrowths formed • Two Young ones are formed of same size. • A single young one forms much smaller to its parents. • Parent body loses its identity • Parents body maintains its identity. • Division of body is symmetrical. • Division of body is asymmetrical.
  16. Fragmentation:  Fragmentation is the process of breaking a piece of organism followed by cell division of mitosis.  The broken part can become an independent adult.  The reproduction of Spirogyra, a green Algae well-known examples of fragmentation.  Besides Spirogyra this is very common among cyanobacteria, molds, lichens.  The fragmentation capacity depends on the complexity of the organism. It may or may not be intentional and may occur naturally or by predators.
  17. Fragmentation in Spirogyra
  18. Regeneration:  Regeneration is a modified form of fragmentation. It is known as a process that makes genomes, cell organs, organisms and ecosystems resistant after alterations or damage.  All species that live on earth can regenerate, but only a few species use it as a method of asexual reproduction, thus producing new individuals for their body parts.  Flat planar worms are highly adapted with regeneration capabilities due to their asexual reproduction methods. Among vertebrates, tail amphibians (salamanders and newts) and certain lizards (geckos) are highly adapted to regenerate their limbs, tails, jaws, eyes and certain internal organs.  As they are more complex multicellular animals, they cannot use regeneration to reproduce or as an asexual reproduction method.  Starfish also have the same ability to regenerate their arm, but unlike amphibians and tail lizards, the lost arms of starfish could regenerate a whole new organism.
  19. Regeneration in Starfish Regeneration in Wall-lizard
  20. Sporulation or Spore formation: Spore are single celled minute propagules produced by several organisms specially fungi, which are able to develop into an complete organism. Spores can be form, Exogenous; and Endogenous
  21. Difference between Fragmentation and Regeneration: Fragmentation Regeneration • Take place in multi-cellular organism having simple body organization. • Take place in fully-differentiated multi-cellular organism having complex body organization. • Each and every piece of body produces new organism. • Each and every piece of body may not develop in a new organism. • No specialized cells are involved. • Specialized cells proliferate and form a mass of cell. Each cell of mass differentiate to new cells and tissues.
  22. Vegetative Propagation:  Vegetative propagation is a form of asexual reproduction of a plant  Vegetative Propagation defined as a mode of asexual reproduction where non-reproductive parts of plants are involved in the production in new organism. Vegetative Propagation Natural Artificial Cutting Layering Grafting Tissue Culture
  23. Natural Vegetative Propagation  Natural vegetative propagation happens when plants grow and develop naturally without human interventions.  Vegetative propagation take place with the help of several plant structures including Roots, Shoots & Leaves.  Vegetative plant structures that arise from plant stems include rhizomes, runners, bulbs, tubers, and corms.  Tubers can also stretch from roots.  Plantlets emerge from plant leaves.
  24. Rhizomes  Vegetative propagation may occur naturally through the development of rhizomes.  Rhizomes are modified stems that typically grow horizontally along the surface of or beneath the ground.  Rhizomes are storage sites for growth substances such as Protein and Starches.  As rhizomes extend, roots and shoots may arise from segments of the rhizome and develop into new plants.  Certain grasses, lilies, irises, and orchids propagate in this manner. Edible plant rhizomes include ginger and turmeric. Rhizome of Ginger
  25. Runners or Stolon  Similar to rhizomes in that they exhibit horizontal growth at or just below the soil's surface. Unlike rhizomes, they originate from existing stems.  As runners grow, they develop roots from buds located at nodes or their tips.  Intervals between nodes (internodes) are more widely spaced in runners than in rhizomes.  New plants arise at nodes where shoots develop. This type of propagation is seen in strawberry plants and currants. Runners of Strawberry
  26. Tubers  These are vegetative organs that may develop from stems or roots.  Stem tubers arise from rhizomes or runners that become swollen from storing nutrients.  The upper surface of a tuber produces a new plant shoot system (stems and leaves), while the bottom surface produces a root system. E.g., Potatoes and yams  Root tubers originate from roots that have been modified to store nutrients. These roots become enlarged and may give rise to a new plant. E.g., Sweet potatoes and Dahlias Shoot Tuber of Potato
  27. Bulbs:  These are the round, swollen parts of a stem that are typically found underground.  Within these organs of vegetative propagation lies the central shoot of a new plant.  Bulbs consist of a bud that is surrounded by layers of fleshy, scale-like leaves.  These leaves are a source of food storage and provide nourishment to the new plant.  Examples of plants that develop from bulbs include onions, garlic, shallots, hyacinths, daffodils, lilies, and tulips. Bulb of Garlic
  28. Corms  These are enlarged bulb-like underground stems.  These vegetative structures store nutrients in fleshy, solid stem tissue and are typically externally surrounded by papery leaves.  Due to their physical appearance, corms are commonly confused with bulbs.  The major difference is that corms contain solid tissue internally and bulbs have only layers of leaves.  Corms produce adventitious roots and possess buds that develop into new plant shoots. Plants that develop from corms include crocus, gladiolus, and taro. Corm of Gladiolus
  29. Artificial Vegetative Propagation  Artificial vegetative propagation happens when plants grow and develop naturally with human interventions.  Human beings exploits the properties of plants of being vegetatively propagate.  There are several methods that can be applied for Vegetative Propagation in Plants
  30. Cutting:  A part of a plant, typically a stem or leaf, is cut off and planted.  Adventitious roots develop from the cuttings and a new plant forms.  Cuttings are sometimes treated with hormones before being planted to induce root development.  Example- Rose plants are generally planted by cuts of their stem.
  31. Grafting:  It is simply a method of joining the vascular tissues of two different plants one over other  In grafting, a desired cutting or scion is attached to the stem of another plant that remains rooted in the ground.  The tissue systems of the cutting become grafted into or integrated with the tissue systems of the base plant over time. Types of Grafting
  32. Layering  This method involves bending plant branches or stems so that they touch the ground.  The portions of branches or stems in contact with the ground are then covered with soil.  Adventitious roots or roots that extend from structures other than plant roots develop in the parts covered by soil and the attached shoot (branch or stem) with new roots is known as a layer. Types of Layering
  33. Plantlets  These are vegetative structures that develop on some plant leaves.  These miniature, young plants arise from meristem tissue located along leaf margins. Upon maturity, plantlets develop roots and drop from leaves.  They then take root in the soil to form new plants. An example of a plant that propagates in this manner is Kalanchoe.  Plantlets may also develop from the runners of certain plants such as spider plants. Leaf of Bryophyllum
  34. Tissue Culture:  This technique involves the culturing of Plant cells that may be taken from different parts of a parent plant.  The tissue is placed in a sterilized container and nurtured in a special medium until a mass of cells known as a callus is formed.  The callus is then cultured in a hormone-laden medium and eventually develops into plantlets. When planted, these mature into fully grown plants. Steps of Tissue Culture
  35. Sexual Reproduction:  Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex.  These gametes fuse to form the zygote which develops to form the new individual. Advantages of Sexual Reproduction:
  36. Reproductive Cycle in Plants:  Annual Plants: These plants complete their life cycle in one year and then must start from seeds or cuttings the next year. Look for annuals near the beginning of the frost-free planting season. E.g.,  Biennial Plants: These plants have a two-year life cycle, and this category is lesser known category. Biennial plants grow leaves, stems and roots the first year, then go dormant for the winter. In the second year the plant will flower and produce seeds before dying. E.g.,  Perennial Plants: These plants live for at least three years assuming wild animals and poor weather don’t kill them first. They will come back year after year from their own overwintering roots even though their foliage may die to the ground after frost. Perennials are sold throughout and often beyond the growing season. E.g.,
  37. Source: i-eBrochure.pdf Unusual Reproductive Cycle in Flowering Plants: Flowers of Bamboo.
  38. Breeding in Animals:  Seasonal Breeders: They reproduce at particular period of the year such as frog, lizards, most birds, deer, etc.  Continuous Breeders: These animals can breed or mate throughout the year. This includes humans and apes (chimpanzees, gorillas, orangutans, and gibbons), who can have a child at any time of year.  Among continuous breeders, the majority of mammals become sexually- receptive (express estrus) and ovulate spontaneously at defined intervals. The female will only allow the male to mate during a restricted time coinciding with ovulation.  The females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase.  Hence, Mammals can exhibit either- Oestrus Cycle Menstrual CycleOR
  39. Differences between Oestrous Cycle & Menstrual Cycle: Oestrus Cycle Menstrual Cycle • It occurs in non-primates such as cows, dogs, etc. • It occurs in primates (monkeys, apes and human beings) only. • It consists of a short period of oestrous or heat (e.g., 12-24 hours in cow) followed by anoestrous or passive period. • This cycle consists of menstrual phase, proliferative phase and the secretory phase. • Blood does into flow in this cycle. • Blood flows in the last few days of this cycle. • The broken endometrium is reabsorbed. • The broken endometrium is passed out during menstruation. • Sex urge is increased during oestrous period. • Sex urge is not increased during menstruation. • Female permits copulation only during oestrous period. • Female does not permit copulation during menstrual phase of the cycle.
  40. Events of Sexual Reproduction: Events in Sexual Reproduction Pre-fertilization Events Gametogenesis Gamete Transfer Fertilization Event Post-fertilization Events Embryogenesis Organogenesis Parturition
  41. 1. Gametogenesis  Gametogenesis refers to the formation of male and female gametes, (Gametes; Genesis=formation).  Gametes can be defined as a mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.  Gametes can be: • Homo-gametes or Isogamous: Gametes are similar in appearance and size, and can not be categorized into male and female gametes. E.g., Cladophora • Hetero-gametes: Gametes are not identical in size, shape and appearance, and hence can be categorize into male and female gametes. Pre-fertilization Events:
  42. 1. Gametogenesis contd..  Hetero-gametes can be:  Anisogamous- Both the male and female gametes are motile but female gametes are greater in size. E.g., Chlamydomonas and members of Basidiomycetes  Oogamous- Here male gametes are motile and female gametes are non- motile, female gametes are usually greater in size. E.g., Human beings  Here, male gametes are called as antherozoid or sperm while female gametes are called ovum or egg.
  43. Sexuality in organisms: Phenomenon of occurrence of male and female sex organs in same or different body. Sexuality Homothallic & Monoecious: Represent bisexual condition. Heterothallic & Dioecious: Represent unisexual condition. Note: • There is another condition too called Hermaphrodite, that represent condition when a organism is bisexual but exchange their gametes for fertilization. • In unisexual flowers, Male is called staminate and female is called pistillate.
  45. Cell division during Gametogenesis:  In an organism having haploid type of parental body gametogenesis take place by the Mitotic Division. For example, Monera, fungi, algae and bryophytes.  In an organism having diploid type of parental body gametogenesis take place by the Meiotic Division. For example, Gymnosperms and Angiosperms and in Animals and Human Beings.  In these organisms specialized cells called meiocytes or gamete mother cells under go meiosis to give rise gametes.
  46. Gamete Transfer:  To facilitate the events of fertilization it is required that male and female gametes come to each other.  The purpose is fulfilled by the process called Pollination in the case of plants while copulation in the cases of animals.  In majority organisms male gamete is motile where as female is stationary. Exceptions , a few fungi and algae both types of gametes are motile.  Gametes posses flagella for the movement and require a medium.  In algae, bryophytes and pteridophytes, water serve as the medium for gamete transfer.  To compensate loss of male gametes during transport, the number of male gametes produced is several thousand times the number of female gametes produced.
  47. Fertilization:  It is a very crucial step of Sexual reproduction.  It is the fusion of male and female gametes to give rise a zygote.  The process is also called as Syngamy.  Fertilization can be:  External; or  Internal
  48. External and Internal Fertilization External Fertilization Internal Fertilization Syngamy occurs outside of the body of organisms. Syngamy occurs inside of the body of organisms. Large number of gametes (male & female) are released into surrounding medium. Number of ova are less, but large number of male gametes are formed. E.g., Bony fish, Amphibians Etc. E.g., Birds, mammals, earthworm Etc.
  49. Post- Fertilization Events:  The events after zygote formation is called post- fertilization events.  This include formation of embryo and development of embryo into a complete organism.
  50. The Zygote and its Fate:  Zygote is a single cell formed by the fusion of two (male and female) gametes.  Every organism including human being begin its life from single cell zygote.  It is an important link between the previous and next generations.  As gametes are haploid, zygotes are always diploid.  In organisms belonging to fungi and algae, zygote develops a thick wall that is resistant to desiccation and damage and undergoes in a period of rest before germination.  In organisms exhibiting haplontic life cycle, zygote undergoes meiosis and forms meiospores that further propagate to develop new organisms which are haploid.  In higher organisms it undergoes several mitotic divisions and gives rise an embryo.
  51. Embryogenesis:  The formation or development of embryo from a single celled zygote is called embryogenesis.  It take place as result of division mitotic division in zygote and further rapid multiplication of cells and the differentiation of these cells.  Cells are divide to increase their number, while cell differentiation results in the modification of cells to give rise specialized group of cells- tissues and organs to form new organisms. Zygote Increase number of Cells Modified cells Tissues Organs Organisms Cell Differentiation Cell Division (Mitosis)
  52. Types of Animals on the basis of development of zygote:  On the basis of development of zygote inside or outside the body organisms can be: 1. Viviparous- Gives birth directly to a young one. E.g., most of the mammals including Human Beings. 2. Oviparous- Lay fertilized or unfertilized eggs. The eggs are covered by a calcareous shell and laid in a safe environment for incubation after which a young one hatches out. E.g., Birds & reptiles. o Chances of survival of viviparous organisms are greater because of proper parental care.
  53. Post-fertilisation Changes in Flowering Plants-  In flowering plants, fertilization and hence formation of zygote take place inside the ovules.  After fertilization, the sepals and petals of flowers wither (dry) and fall off. In the members of Solanaceae (E.g., Brinjal) sepals remain attached with fruit.  As the zygote develop into embryo, the ovules develop into seeds  Ovary develops into fruit and its wall become thick and fleshy and called pericarp.  Seeds may undergo dormant condition and cease their metabolic activities and during favorable condition germinate into new plants.
  54. Unusual Modes of Reproduction:  Apomixis: It is an asexual reproduction that occurs without fertilization and not involving meiosis. One example of apomixis is the apomictic parthenogenesis. It its one in which the egg cell is produced through mitosis. It then develops directly into an embryo without the prior fertilization. E.g., Rubus (brambles or blackberries),  Parthenogenesis: Reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants. Cyclic parthenogenesis is well displayed in aphids. Parthenogenesis never produces viable embryos, though, because unfertilized eggs lack specific instructions about gene expression from the sperm.  Neotany: This is the condition in which an organism reaches maturity without losing all of its juvenile characteristics. Typical examples would include becoming sexually viable while still in a larvae stage or retention of gills in an adult. E.g.,
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