22.2, Reproduction in flowering plants

• Reproduction in flowering plants

  Takes place within flowers
• Flowers


  • Contain reproductive organs protected by specialized leaves
• Sepals


  Modified leaves that protect the flower, often green but can be brightly colored

  
• Petals


  Modified leaves, brightly colored to attract animal pollinators
• Tepals


  When sepals and petals are the same color
• Tepals occur in monocot flowers, such as lilies
• Flowering plants that use wind pollination usually have small sepals and petals, or even none at all
• Stamen


  • The male structure of a flower, has a stalk (filament) that supports an anther which produces pollen grains
• Carpel


  • The female structure of a flower, often several carpels join together forming a pistil, with a stigma, style and ovary
• Pollination


  1. Pollen grain reaches the stigma of the same plant species

  2. Wind-pollinated flowers are small and produce large amounts of pollen

  3. Insects, birds, and other animals pollinate flowers with bright colors or sweet smells

  4. Animal visits a flower, gets dusted with pollen, and transfers it to another flower
• Wind pollination


  Requires a lot of energy
• Animal pollination


  More direct and efficient than wind pollination
• Flower parts


  • Part of the sporophyte, gametophytes are tiny and enclosed in the flower
• Male gametophyte formation


  1. Cells in anthers divide by meiosis to produce four male haploid spores

  2. Each spore divides by mitosis to produce two haploid cells, forming a single pollen grain
• Female gametophyte formation


  1. One cell in the ovule divides by meiosis to produce four female spores

  2. Nucleus of one spore divides by mitosis three times, forming seven cells including an egg and two polar nuclei
• Double fertilization


  1. Pollen tube extends down the style to the ovule

  2. One sperm fertilizes the egg

  3. Other sperm joins with the two polar nuclei to form the endosperm

  
• Double fertilization


  Flowering plants only use energy to make a food supply if an egg is fertilized
• Double fertilization


  Gives flowering plants an advantage that energy is not wasted if an egg is not fertilized
• Seed formation


  1. Ovule becomes a seed with a seed coat protecting the embryo and endosperm

  2. Embryo develops one or two cotyledons (seed leaves)

  3. Ovary develops into a fruit