Reproduction in Plants

• Reproduction


  The production of new organisms to ensure the continuity of species
• Types of reproduction


  • Asexual reproduction
  • Sexual reproduction
• Asexual reproduction


  The production of genetically identical offspring from one parent
• Sexual reproduction


  The process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring

  
• Asexual reproduction requires one parent
• Offspring from asexual reproduction are genetically identical to the parent
• Asexual reproduction in plants

  • via tubers, bulbs, runners
  • offspring is genetically identical to parent plant

  
• Strawberry plant reproduction


  Asexual reproduction

  
• Sexual reproduction requires two parents
• Offspring from sexual reproduction are genetically different from the parents
• Comparison of asexual and sexual reproduction

  • No. of parents required
  • Genetic composition of offspring
  • No. of offspring produced in a period of time

  
• Mating rituals
• Parts of a Flower


  • Petals (sum of petals = corolla)
  • Sepals (sum of sepals = calyx)
  • Receptacle
  • Stalk (pedicel)
  • Stamen (anther, filament)
  • Carpel (stigma, style, ovary, ovule)

  
• Sepals


  • Protect the flower petals in the bud stage
• Insect pollinated flower diagram

  • stamen

  
• Flowers


  • Identify the bisexual and unisexual flower
• Pollination


  Transfer of pollen grains from the anther to the stigma of flowers of the same species

  
• Self-pollination


  Transfer of pollen grains from the anther to stigma of flowers of the same plant (of same species)

  
• Cross-pollination


  Transfer of pollen grains from the anther to the stigma of flowers of different plants of the same species

  
• Self-pollination


  • Distance travelled by pollen grain is shorter (anther to stigma within same plant)
  • Aid needed for pollination is not necessary

  
• Cross-pollination


  • Distance travelled by pollen grain is longer (from one plant to another plant)
  • Animal or wind aid needed for pollination

  
• Self-pollination


  Genetic composition of offspring is genetically similar
• Cross-pollination


  Genetic composition of offspring is genetically different
• Types of flowers


  • Bisexual flowers
  • Unisexual flowers
• Position of stigma and anthers in bisexual flowers

  • Stigma below anther (pollen falls onto stigma easily)
  • Stigma above anther (pollen less likely to fall onto stigma)
• Maturing of flowers in bisexual flowers

  • Stamens mature first
  • Carpels mature later
• Protandry in bisexual flowers

  Strategy to prevent self-pollination
• Advantages of self-pollination


  • Higher success rate: one parent needed
  • Does not depend on wind or animal assistance
  • Less pollen wasted
• Disadvantages of self-pollination


  • Offspring has less genetic variation
  • Offspring higher chance of recessive alleles expressed
• Advantages of cross-pollination


  • Offspring genetically more different
  • Seeds produced are more viable
• Disadvantages of cross-pollination


  • Lower success rate: two parents required
  • Depends on wind or animal assistance
  • More pollen wasted
• Asexual reproduction, self-pollination, and cross-pollination result in offspring with different genetic compositions
• Cross-Pollination


  Transfer of pollen grains from the anther to stigma of flowers of same species by pollinators or wind

  
• Pollination types


  • Animal-pollination
  • Wind-pollination
• Animal-pollination


  • Assisted by animals (usually insects), which function as pollinators
  • Bats, birds, insects
• Wind-pollination


  • Assisted by wind
• Petals


  Landing platform for pollinators
• Bee-pollinated flowers


  • Have a lobe that serves as a landing pad
  • Anthers often located above the large petal, dusting the back of the bee as it enters

  
• Pollination process


  1. At first flower: ripe anthers rub pollen onto the bee's back

  2. At second flower: pollen grains on bee's back rub against stigma

  
• Bat-pollinated flowers


  • Nocturnal flowers that bloom at night
  • Petals tend to be large and white (or pale coloured) to be easily distinguished between dark surroundings at night
  • Pollen tends to be deposited on faces and head of bat