sexual reproduction in plants

• Sexual reproduction in flowering plants

  Advantage is that offspring have a selection of genes from two parents, so each individual's genes are different. The offspring are not identical, and there is variety in the species.
• Structure of an insect-pollinated flower

  • Flower is a leafy shoot containing the sexual organs of a flowering plant, adapted for sexual reproduction

  
• Parts of the flower

  • Carpel (female part)
  • Stamen (male part)
  • Petal
  • Sepal
  • Receptacle
• Carpel


  Female part of the flower. Includes stigma, style, and ovary.
• Stamen


  Male part of the flower. Includes anther and filament.
• Pollen


  Haploid, single cell, double wall, binucleate (tube nucleus and generative nucleus)
• Pollination

  1. Pollen transfer from anther to stigma

  2. Pollen tube grows down style to ovary

  3. Nucleus of pollen grain fertilises egg cell in ovule

  4. Fertilised egg develops into embryo, ovary becomes fruit, ovule becomes seed

  5. Seed is dispersed and offspring grows

  
• Insect-pollinated flowers


  • Attract pollinators with brightly coloured petals, food rewards (pollen/nectar), fragrance
• Wind-pollinated flowers

  • Have large feathery stigmas, stigmas outside the flower, smooth small pollen easily transported by wind, produce large amounts of pollen
• Advantages and disadvantages of insect vs wind pollination

  • Insect: Less pollen needed, saves energy, but nectar and petals require energy
  • Wind: No need for petals or nectar, but pollen less likely to reach stigma, requires large pollen production

  
• Seed

  Embryo, food store (cotyledons), seed coat

  
• Methods of seed dispersal

  • Wind (light weight, high air resistance, wings/parachutes)
  • Animal (hooks, bright colours, food source)
  • Water (buoyant seed/fruit)
  • Mechanical (explosive pods)

  
• Germination

  1. Oxygen needed for respiration

  2. Water softens seed coat, activates enzymes, transports food

  3. Suitable temperature for enzyme activity
• Hypogeal germination


  • Epicotyl elongates, leaving cotyledons in soil
• Epigeal germination


  • Hypocotyl elongates, pulling cotyledons out of soil