Chap - 14 Reproduction

• Types of reproduction


  • Asexual
  • Sexual
• Asexual reproduction


  • Only one parent
  • Quick process
  • Genetically identical to parent
  • No variation unless due to environment
  • No pollinators required
• Asexual reproduction examples


  • Bacteria
  • Fungi
  • Potato tuber
• Disadvantages of asexual reproduction


  • New plants compete with parent for resources
  • Very little variation
  • Genetically identical, not resistant to disease, may all be killed
• Sexual reproduction


  • Two parents
  • Offspring not genetically identical to parents
  • Brings about variation
• Advantages of sexual reproduction


  • Genetic variation/diversity
  • Allows adaptation to environmental pressure
  • New species can evolve
  • Cross pollination
  • Seed dispersal
  • Can colonise new areas
  • Less competition with parent plant
  • Can survive harsh conditions
• Disadvantages of sexual reproduction

  • Finding a mate uses resources
  • Isolated individual cannot reproduce sexually
• Flowers


  Reproductive organs of plants
• Features of flowers that attract insects/birds


  • Bright color petals
  • Scent
  • Nectar
• Pollen


  Contains male gametes
• Ovules


  Contain female gametes, inside ovaries
• Insect pollination


  Bees land on petals and feed on nectar
• Wind pollination


  1. Anthers hang outside flower and release pollen

  2. Stigmas are feathery and catch pollen in air
• Differences between insect-pollinated and wind-pollinated flowers


  • Insect-pollinated: Large conspicuous petals, often scented, have nectaries, anthers/stigma inside flower
  • Wind-pollinated: Small or no petals, no scent, no nectaries, anthers/stigma hang outside flower
• Pollination


  Transfer of pollen from anther to stigma
• Types of pollination


  • Self-pollination
  • Cross-pollination
• Advantages of self-pollination


  • Only one plant needed
  • Greater chance of pollination
  • Successful if no other plants nearby
  • Less pollen wastage
  • Not dependent on pollinators
• Disadvantages of self-pollination


  • Less variation
  • Increased competition
  • All plants adapted to same environment
  • Less chance of surviving
  • Risk of extinction
  • Increased chance of genetic disease
  • Susceptible to same disease
• Advantages of cross-pollination


  • Allows variation/genetic diversity
  • Plants more likely to survive environmental pressure
  • Increased resistance to disease
• Fertilisation


  1. Pollen grain lands on stigma

  2. Pollen tube grows down to ovule

  3. Male gamete nucleus fuses with egg cell nucleus to form zygote
• Zygote


  Formed by fusion of male and female gamete nuclei
• After fertilisation


  1. Zygote divides by mitosis to form embryo

  2. Ovule becomes a seed

  3. Ovary becomes a fruit