MOD 1

• Plant sexual reproduction


  Usually depends on pollinating agents
• Plant asexual reproduction


  Independent of pollinating agents
• Flowers


  • Often the showiest or most strongly scented part of plants
  • With their bright colors, fragrances, and interesting shapes and sizes, flowers attract insects, birds, and animals to serve their pollination needs
• Pollination methods


  • Insects
  • Birds
  • Animals
  • Wind
  • Water
  • Self-pollination
• Plant reproduction


  • Some plants reproduce sexually, others asexually
  • Sexual reproduction usually depends on pollinating agents, asexual reproduction is independent of these agents
• Flowers


  • Showiest or most strongly scented part of plants
  • Attract insects, birds, and animals to serve their pollination needs
  • Some plants pollinate via wind or water, others self-pollinate
• Sexual reproduction in plants

  1. Gametophyte stage

  2. Sporophyte stage

  3. Haploid gametophyte produces male and female gametes by mitosis

  4. Fusion of male and female gametes forms diploid zygote

  5. Diploid sporophyte produces spores by meiosis

  6. Spores divide by mitosis to produce haploid gametophyte
• Stages in the alternation of generations

  • Diploid sporophyte has sporangium
  • Sporangium undergoes meiosis and forms haploid spores
  • Spore develops into haploid gametophyte
  • Gametophyte has reproductive organs which form haploid gametes
  • Gametes fertilize to form haploid zygote which matures into sporophyte
• Life cycle of higher plants

  • Dominated by sporophyte stage, with gametophyte borne on sporophyte
  • In ferns, gametophyte is free-living and distinct from sporophyte
  • In bryophytes, gametophyte is more developed than sporophyte
• Vegetative and reproductive phases of plant growth

  1. Vegetative phase: increase in size, produce shoot and root system

  2. Reproductive phase: some branches bear flowers
• Flowers


  • Borne singly or in clusters
  • Borne on a stalk called receptacle
  • Flower shapes, color and size are unique to each species and used for plant classification
• Gametophyte


  Haploid stage that alternates with diploid sporophyte during sexual reproduction in angiosperms
• Main parts of a typical flower

  • Calyx
  • Corolla
  • Androecium
  • Gynoecium
• Gymnosperm life cycle


  • Alternation of generations
  • Sporophyte is the green leafy part
  • Cones contain male and female gametophytes
  • Female cones are larger and positioned at the top
  • Male cones are smaller and positioned at the bottom
• Gymnosperm pollen is shed and blown by the wind


  Makes it difficult for gymnosperms to self-pollinate
• Asexual reproduction


  • Produces plants genetically identical to parent
  • Survives well under stable environmental conditions compared to sexually reproduced plants
• Advantages of asexual reproduction

  • Resulting plant reaches maturity faster
  • Resulting plant is sturdier than a seedling
• Methods of asexual reproduction


  • Natural (growth from stem buds, adventitious roots/runners, leaf buds)
  • Artificial (grafting, cutting, layering, micropropagation)
• Pollination


  The process of transfer of male gametes (pollen grains) in plants from the male reproductive part (anther) to the female reproductive part (stigma)
• Pollination is the prerequisite of fertilization in plants as it ensures the movement of gametes in otherwise immobile plants
• Pollinating agents


  • Wind
  • Water
  • Insects
  • Animals
• Self-pollination

  The process where plants themselves result in pollination, occurring mostly in closed flowers
• Transfer of gametes occurs within the same species

  A hybrid will be formed if the transfer occurs between different species
• Pollination in non-flowering plants

  • Pollen is caught in the fluid secreted by the ovule as the ovules are exposed
• Pollination in flowering plants

  • Ovules are enclosed within a structure termed pistil and thus require pollination by external agents
• Pollen grain preparation for pollination

  1. Pollen grains undergo dehydration to reduce their mass so that they can be easily moved from one flower to another

  2. Hydration and activation of pollen grains occur once they land on the stigma before the formation of the pollen tube
• Pollination agents


  • Abiotic (wind, water, rain)
  • Biotic (insects, birds, animals)
• Fertilization

  The process of fusion of haploid male and female gametes to form a diploid zygote, resulting in the initiation of the development of a new individual
• Fertilization follows pollination in plants
• Fertilization in plants

  1. Hydration and activation of pollen grains

  2. Formation of pollen tube

  3. Pollen tube penetrates stigma and elongates along style, reaching ovary

  4. Pollen tube penetrates ovule through micropyle and bursts in embryo sac, releasing sperm
• In gymnosperms, the formation of the pollen tube doesn't occur as the ovules are not enclosed with the ovary
• Double fertilization

  In angiosperms, two sperms from each pollen tube fertilize two cells present in the ovary
• Perfect flowers

  Flowers that contain both stamens and carpels, allowing self-pollination
• Biochemical and anatomical barriers to self-pollination promote cross-pollination
• Self-pollination is a severe form of inbreeding and can increase the number of genetic defects in offspring
• Monoecious plants

  Plants that have both male and female flowers on the same plant
• Dioecious plants

  Plants that have male and female flowers on separate plants
• Reproduction in Animals

  Animals produce offspring through asexual and/or sexual reproduction
• Sexual Reproduction

  • Combination of (usually haploid) reproductive cells from two individuals to form a third (usually diploid) unique offspring
  • Produces genetically diverse offspring that differ from their parents
  • Gives species a better chance of surviving in an unpredictable or changing environment
  • Requires two different types of individuals, males and females, which can limit the ability to colonize new habitats
• Hermaphroditism

  • Animals where one individual has both male and female reproductive parts
  • Invertebrates such as earthworms, slugs, tapeworms, and snails are often hermaphroditic
  • Hermaphrodites may self-fertilize or may mate with another of their species, fertilizing each other and both producing offspring
  • Self-fertilization is common in animals that have limited mobility or are not motile, such as barnacles and clams