Plant reproduction:

       Flowers are reproductive structures in plants [Fig. 31.9A, p. 634]:

              Sepals - cover/protect the flower before it opens.

              Petals - the brightly colored parts of the flower (if it is colored).

              Stamens - male reproductive parts. Composed of:

                      anthers - where pollen develop and are stored

                      filaments - structures holding up anthers

              Carpels - female reproductive parts. Composed of:

                      stigma - at tip of carpel, where pollen are placed.

                      ovary - contain ovules, which hold eggs and supporting cells.

       Fertilization [Fig. 31.10, p. 635]:

              - egg or sperm are also known (in plants) as gametophytes. These are haploid
              (have half the number of chromosomes).

                      - in this case, though, the gametophytes generally make just sperm and/or
                      egg. They don't make an “individual”.

              - sperm formation is pretty straight forward. By meiosis, four haploid “spores”
              develop.

                      - but again, in this case, the “spores” don't really make an “individual” like
                      in mosses or ferns - instead they go almost directly to making egg or
                      sperm (and a few associated structures)

                      - each spore then divides again, forming a tube cell and generative cell.

                              - the tube cell eventually forms a tube leading to the ovary

                              - the generative cell eventually divides yet again, and forms two
                              “sperm” cells.

                      - but before this happens, the tube cell and generative cell are put together
                      in a pollen grain.

              - Pollen grains are distributed either through:

                      - wind, or

             - insects (hence the bright colors & nectar associated with flowers).

      - Pollination occurs if the pollen lands on the stigma of the correct species (lots of
      variation in this, though).

             - once this happens, the tube cell begins to make it’s tube, and the
             generative cell divides to make two sperm cells.

             - tube grows downwards towards ovary and ovules.

                        - grows around (underneath) one ovule, and enters the “embryo
                        sac”

      - In the ovule:

             - a central cell divides into four haploid spores (through meiosis).

                        - three of these degenerate

                        - remaining one survives, enlarges, and divides, making:

                               - an embryo sac

                                       - this has a large central cell with two haploid
                                        female nuclei.

                               - and an haploid egg

      - as sperm enter ovule:

             - one fertilizes the egg (now diploid)

             - one fertilizes the central cell.

                        - note that since this contains TWO haploid nuclei, the resulting
                        cell is actually triploid (has two haploid copies of the female genes,
                        and one haploid copy of the male genes)

             - this process is termed double fertilization.

Seed development [Figs. 31.11A & 31.11B, p. 636]:

      - the triploid central cell divides and forms the “endosperm”, which is rich in
      nutrients for the embryo

      - the zygote (fertilized egg) develops into the embryo. This will have either one
      or two leaves, based on whether or not it’s a monocot or dicot.

       - the ovule forms a seed coat that protects and encloses both the endosperm and
       embryo.

       - the seed can then lie dormant until conditions are right for germination (i.e.,
       embryo grows out of seed coat).

              - some seeds can be dormant for many years (hundreds or more).

Fruit development [Figs. 31.12 A & B, p. 637]:

       - The ovary develops into a structure that stores and protects seeds.

       - Apples, raspberries, pineapples are all examples of different kinds of fruit.

              - edible fruits are designed to be attractive so that animals will spread the
              seeds around.

                      - seeds usually survive the trip through the digestive system, and
                      are then deposited with rich fertilizer.

              - in lab the differences in fruit types will be examined (see also p. 635 /
              5th: p. 639).

Seed germination [Fig. 31.13A & B, p. 638]:

       - seeds often germinate in response to water. Water ruptures the seed coat, and
       allows the embryo to start growing.

              - embryo starts to use food and grow

              - dicots: generally, root starts to grow downwards, followed shortly by the
              shoot.

                      - shoot has a hook in it (tip is bent over) to prevent damage to the
                      tip before it breaks the soil surface.

                      - hook straightens out in response to light

              - monocot: root starts only just before shoot.

                      - shoot is covered in protective sheath

                      - once through the surface, the shoot grows through the sheath (the
                      sheath is used like a “tunnel”.

Asexual reproduction:

       plants readily grow by asexual reproduction:

              - fragmentation

              - runners

              - root sprouts

              - cuttings

              - much of our agriculture depends on asexual (vegetative) reproduction

                        - fruit trees in particular, but also raspberries, potatoes, etc.