BIO01 4Q

• Reproduction


  Biological process by which new individuals of the same species are produced, ensuring the continuation and survival of that species
• Modes of reproduction


  • Asexual reproduction
  • Sexual reproduction

  
• Asexual reproduction


  A single parent produces offspring without the involvement of gametes or fertilization. The offspring is genetically identical or nearly identical to the parent, as there is no genetic recombination
• Sexual reproduction


  Two parents contribute genetic material to produce offspring. Specialized cells called gametes, which are produced by the reproductive organs, combine to form a new organism. The offspring inherits a combination of genetic material from both parents, resulting in genetic diversity
• Hydrilla (Hydrilla verticillata) is a submerged aquatic plant that can reproduce asexually
• Stages in the plant life cycle


  • Sporophyte generation
  • Gametophyte generation

  
• Sporophyte generation


  Diploid (2n), dominant in flowering plants, produces flowers - the reproductive structure in angiosperms
• Gametophyte generation


  Haploid (n), produces microspores (male gametophyte - pollen) and megaspores (female gametophyte - embryo sac within the ovule)
• Alternation of generations


  Plants alternate between a haploid gametophyte stage and a diploid sporophyte stage in their life cycle
• In the life cycle of angiosperms, the diploid sporophytic phase is the plant body itself, which is the larger and more prominent phase. Sexual maturity is characterized by the presence of flowers

  
• The haploid gametophytic phase is small and is represented by the stages from the megaspores to egg and the microspore to the male gametophyte, which are developed inside the flowers via meiosis
• The megaspore and the microspore undergo double fertilization which results in the formation of seeds
• When the seed germinates, it develops into a new plant to produce a sporophyte generation

  
• The sporophytic plant produces the flower which bears the spores which later give rise to the male gametophyte. The male gametophyte gives rise to two sperms which fuse with the two cells of the 7-celled female gametophyte which is present within the ovule
• Double fertilization is the characteristic feature of the angiosperms. Two sperms fertilize the two cells of the female gametophyte which results in the formation of a zygote which later forms the embryo and the other fusion products forms the triploid nutritive tissue known as the endosperm which nurtures the developing embryo

  
• Flower structure


  • Sepals
  • Petals
  • Stamens
  • Carpels

  
• Complete flower structure


  Presence of all the structures listed above

  
• Incomplete flower structure


  Absence of one or more structure/s listed above
• Gametophyte formation in angiosperms involves the development of pollen grains, which contain the male gametes, and the formation of ovules, which house the female gametes
• An anther from a flower gives a pollen sac with microspore mother cell in sporophyte (2n). In the gametophyte (n), under meiosis gives microspores and under mitosis gives pollen grains (microgametophytes) with generative cell and tube cell nucleus. In the sporophyte (2n), megaspore mother cell in ovule under meiosis gives megaspores, and degenerated megaspores under mitosis gives eight-nucleate embryo sac (megagametophyte) with antipodals, egg cell, polar nuclei, and synergids
• Megaspore


  • Female sex cell
  • Located in the ovary
  • 4 megaspores produced after meiosis, 1 used in fertilization, rest degraded
  • Undergoes 3 rounds of mitosis to produce 8 nuclei
  • Nuclei are haploid (n)
  • 3 antipodal nuclei, 2 central nuclei, 2 synergid nuclei, 1 egg cell

  
• Pollen grain


  • Contains degenerative cell which becomes the sperm cell
  • Contains tube cell which becomes the pollen tube
• Double fertilization takes place when the sperm cell fertilizes the central nuclei (develops into endosperm, triploid) and the egg cell (develops into embryo, diploid)

  
• Modes of asexual reproduction in plants

  • Runners and stolons
  • Rhizomes
  • Tubers
  • Bulbs
  • Cuttings
  • Grafting

  
• Vegetative propagation


  Involves the generation of new individuals without the involvement of seeds, through stems, roots and leaves
• Most animals reproduce sexually, requiring meiosis to produce haploid gametes (sperm and eggs) which unite by fertilization to produce the diploid zygote that develops by mitosis into a new multicellular organism

  
• Animal reproductive organs


  • Testes (produce sperm)
  • Ovaries (produce eggs)
• Parthenogenesis


  Modification of sexual reproduction where an unfertilized egg develops into a complete individual, a form of asexual reproduction found in some animals

  
• Sexual reproductive systems in organisms

  • Dioecious (separate sexes)
  • Monoecious (hermaphroditic, containing both male and female sex organs in a single body)
• Modes of fertilization


  • External fertilization (gametes unite outside the body)
  • Internal fertilization (gametes unite inside the body)
• Developmental strategies


  • Oviparity (fertilized eggs deposited outside mother's body to complete development)
  • Ovoviviparity (fertilized eggs kept within mother to complete development, young obtain food from egg yolk)
  • Viviparity (young develop within mother and obtain nourishment from her blood)

  
• Budding is a form of asexual reproduction in animals where a new individual forms as an outgrowth or "bud" on the parent organism, which then detaches and becomes an independent organism
• Animals with viviparity


  • Mammals (such as humans, dogs, cats, and whales)
  • Some reptiles (such as some species of skinks and boas)
  • Certain sharks and rays
  • Some fish
• Viviparity


  In viviparous animals, both fertilization, as well as the development of the embryo, takes place inside the female reproductive system. Once the fetus development is complete, the mother delivers the baby.
• Placental mammals are viviparous
• Characteristics of placental mammals

  • Do not lay eggs
  • Placenta allows exchange of material between mother and developing embryo
  • Placenta derived in part from chorion membrane
  • Development occurs inside the female's body
  • Care of zygote and embryo
  • Eliminate need for shelled egg

  
• Budding


  Formation of a new individual as an outgrowth or "bud" on the parent organism. Once developed, the bud detaches and becomes an independent organism.
• Hydra reproduces asexually through budding
• Fragmentation


  Some animals can regenerate from fragments of their bodies. Each fragment has the potential to develop into a complete organism.
• Starfish can reproduce asexually through fragmentation