3: plant reproduction

• Plants can reproduce asexually through vegetative means to propagate genetically identical offspring. They can also reproduce sexually with male and female gametes to increase genetic diversity.
• Plants can be vegetatively propagated through stems, tubers, young shoots, and stems.
• Sexual reproduction utilizes the fusion of male and female gametes to produce a zygote, which is followed by seed production.
• Male gametes in plants are the pollen grains, produced in anthers.
• Female gametes in plants are the ovules, produced in the ovary.
• The male and female gametes of a plant are found in flowers.
• Pollination describes the transfer of the male pollen to the female stigma.
• Pollen can be transferred via the wind or insects
• Cross pollination is the transfer of pollen from one plant to the stigma of another plant.
• A fruit is formed following pollination, and typically contains seeds.
• steps of double fertilization:

  • pollen grain germinates on the stigma of the same plant species and produces a germ tube, which is grown down the style.
  • When the pollen reaches the ovary, it goes through the micropyle within the ovule
  • the one nuclei of the 2 sperm nuclei fuse with the egg nucleus inside the ovule to form the zygote (2n)
  • the second nuclei fuses with the 2 polar nuclei to form the endosperm (3n) which serves as food
• Development of a zygote

  • division of the zygote several times forms a embryo
  • zygote differentiates to form a root and shoot apex
  • ovary expands and the wall becomes the seed coat
  • each fertilized ovule forms one seed
  • can have one or two cotyledons depending if monocot or dicot
• To survive, plants have to produce lots of seeds and spread them as far as possible.
• Evolutions of to spread plant seeds include:

  • seeds that spread by wind
  • seeds that float on water
  • spiny seeds that latch on and travel by animals
  • aerodynamic seeds
  • fleshy and attractive fruits to be eaten