Chapter 39

Reproduction in plants

aka. How plants have sex

aka. Plant sexy time

• Most flowering plants display sexual reproduction
  • Two gametes fuse to produce offspring with a unique combination of genes
• They undergo Alternation of Generations 
  • Two multicellular life cycle stages
  • diploid
    • Spore producing sporophyte
      • produces spores by meiosis
        • a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.
  • haploid
    • Gamete producing gametophyte
      • produces gametes by mitosis
        • a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
• Egg is Female
• Sperm is Male

Evolutionary Trends in the Plant Kingdom

• Sporophyte has become larger, more complex
  • Flowering plants
    • Sporophyte independent 
    • Dependent gametophyte is only a few cells contained within flowers
• Gametophyte has become smaller, less complex
  • Moss
    • Sporophytes small and dependent on gametohyte (Dominant form)
• Female
  • 7 cells
• Male
  • 2-3 cells

Flower and Sexual Cycle

• Flowers
  • ONLY in angiosperms
  • All sizes, shapes, colors, and aromas
• Essential process of Sexual reproduction occurs within flowers
  • Meiosis/cytokenesis
    • reduces chromosome number
  • Syngamy (fertilization)
    • restores chromosome number

"Ideal" Flower

• Uses highly modified leaves arranged in whorls (circular) at the tip of a highly modified stem
• A flower is a highly modified determinate (short term) shoot system

• Pedical, receptical, 4 sets of highly modified leaves are all 2N and part of the sporophyte generation
• Pollen (sperm) and eggs of embryo sac are part of the 1N generation
• Pedical
  • flower stalk
• Recepticle
  • tip of modified stem with 4 whorls attached

Sexual Cycle