Plant Reproduction

• Reproduction

  Fundamental for passing on genes and species continuity
• Types of reproduction

  • Asexual
  • Sexual
• Asexual reproduction


  • Involves one parent, seen in bacteria, fungi, plants, and some animals
  • Examples include budding, fission, fragmentation, and parthenogenesis
  • Offspring are genetically identical clones
  • Advantages include rapid production of offspring in stable environments, but disadvantages include low genetic variation and susceptibility to harmful mutations
• Sexual reproduction

  • Requires two parents, involves union of specialized gametes through meiosis
  • Offspring are genetically similar but not identical to parents
  • Advantages include genetic variation for adaptation to changing environments
• Causes of genetic variation in sexual reproduction

  1. Occurs during meiosis I through crossing over (exchange of genetic material between homologous chromosomes) and independent assortment (random segregation of homologous chromosome pairs)

  2. Also occurs during fertilization through fusion of male and female gametes, resulting in new combinations of chromosomes in the zygote
• Understanding mitosis and meiosis is essential to comprehend the mechanisms underlying genetic variation in sexual reproduction
• Flowers

  • Reproductive structures in flowering plants (angiosperms) consisting of four layers: petals, sepals, stamens (male), and pistils (female)
• Reproductive structures and cells

  • Stamen: Consists of filament and anther, which holds pollen grains containing generative and tube cells
  • Pistil or carpel: Includes ovary (base), style (stalk), and stigma; contains ovules with embryo sacs
• Pollination


  Transfer of pollen grains to stigma, followed by germination of pollen grains and growth of pollen tube into ovary; facilitated by insects, wind, or water
• Fertilisation


  Fusion of sperm cell with egg to form diploid zygote, and fusion of another sperm cell with central cell to form triploid endosperm; known as double fertilisation, unique to flowering plants
• Insect-pollinated flowers


  • Pollen transfer facilitated by insects, leading to adaptations such as nectar production, strong scents, bright colors, and sticky pollen to attract and retain pollinators
  • Symbiotic relationships between flowers and specific pollinators, such as bees attracted to pea flowers
• Types of Pollination

  • Cross-pollination
  • Self-pollination
• Cross-pollination


  • Transfer of pollen grains between flowers on different plants
  • Facilitated by animals (like insects, birds, and bats) or wind
  • Grasses and cereal crops often pollinated by wind; flowers adapted with light, unscented characteristics
• Self-pollination


  • Transfer of pollen grains to stigma of the same flower or another flower on the same plant
• Mechanisms for Cross-pollination

  • Differentiation of male and female flowers on separate plants (e.g., date palm, papaya)
  • Variation in maturation times of male and female flowers (e.g., avocado)
  • Variation in maturation times of anthers and pistils in hermaphroditic flowers (e.g., ivy, carrot)
  • Anatomical structures in bisexual flowers preventing self-pollination (e.g., primrose)
• Self-incompatibility Mechanisms


  • Variations in flower structure (e.g., length of stamen and style)
  • Genes for self-sterility, with multiple alleles preventing fertilisation between similar plants
• Seed Dispersal

  • Wind-dispersed seeds: Adaptations like wings or hair aid wind dispersal (e.g., dandelion, maple)
  • Water-dispersed seeds: Buoyant seeds with fibrous coverings or specialized structures (e.g., water lilies, coconut)
  • Animal-dispersed seeds: Dispersal via animal consumption or attachment to fur or skin (e.g., burdock)
• Seed Germination

  1. Begins with water uptake, followed by resumption of metabolic activities and mobilisation of food reserves

  2. Conditions include water, favorable temperature, and oxygen

  3. Development stages: Imbibition, respiration, mobilising food reserves, embryo axis development, seedling emergence

  4. Light influences seedling orientation after plumule emergence