BIO 104 4/10/96

Plant Diversity

Review of Pine Life Cycle   SEE FIGURE 28.3
The sporophyte is the entire pine tree
     2 types of cones:
          1) ovulate=seed bearing cone
          2) male =pollen bearing cone
     Ovulate:
          -megaspore mother cell undergoes meiosis
          Within the cone:
          -female gametophyte, the archegonium, and the egg are
          all contained within the cone
      Male Cones:
          Microspore mother cells undergo meiosis to form the male gametophyte (pollen).
     Angiosperms Largest group of organisms on land are the angiosperms.
     They belong to the division anthophyta.  (phyta means plants)
          Angiosperms are the most recent plant in terms of evolutionary time.
     There are roughly 250 thousand species of angiosperms.
     Characteristics:
          1) Contains seeds as do gymnosperms; seeds on which the ovules are enclosed in a carpel and the seeds are borne within the fruits.
          2) Contain fruits, fruits are ripened ovaries with a seed.
          3) Characterized by the flower, which is basically insect pollinated.
               -There are other ways to transfer pollen other than insects.  For example, cacti use insects (moths) and bats at night, birds during the               day.
               -Energy is saved by using third party fertilization.
          4) Female gametophyte is very reduced within the flower and consists of 8                      nuclei and 7 cells. Known as the embryo sac.
          5) Double fertilization
               -2 sperm nuclei fertilize an ovule
                    -1 sperm nucleus and the egg nucleus form the zygote
                    -1 sperm nucleus and 2 polar body nuclei form a 3n endosperm
     2 Classes 
     1) Class Monocotyledon (Monocots)
          -1 cotyledon
          50,000 species
          Characteristics:
               -flower parts are in threes or multiples of three.
               -leaf venation is parallel
               -vascular bundles are scattered in the stem
               -little or no secondary growth mainly grasses or annuals

     2) Class Dicotyledonae (Dicots)
          -2 cotyledons
          -netlike (reticulate) veins
          -flower parts in fours or fives
          -200,000 species
          -vascular bundles in a ring in the stem
          -true secondary growth (trees annual rings are secondary growth)
          -vascular cambium present
               cambium gives rise to new xylem and phloem
Angiosperm Life Cycle
SEE FIGURE 28.4
     Carpel: includes the ovary= within which are ovules with give rise to seeds.
     Anther: this is where male gametophytes form.
     Stigma: Within ovule is a megaspore mother cell 2n, meiosis occurs yielding 4 megaspores
n; 1 megaspore develops and goes through 3 divisions of mitosis yielding 8 nucleate
megagametophytes (embryo sac).
          1 nucleus will be part of the egg
          2 nuclei will be polar nuclei.
     There will be 7 cells as part of the embryo sac:
          1 egg
          2 synergids
          1 central cell containing the 2 polar nuclei
          3 antipodals
     Anther:  microspores arise through meiosis;  pollen grain lands on the stigma and begins to grow a pollen tube down the style, then grows into the female gametophyte.
     1 sperm fertilizes the egg and 1 fuses with the 2 polar nuclei forming the endosperm: double fertilization.
     zygote forms the embryo which forms the seedling.
SEE FIGURE 28.2 FOR DIAGRAM OF ANGIOSPERM LIFE CYCLE
     Female gametophyte
     -pollen tube goes into synergids first then the egg
     Seed
       1) 1 nucleus combines with the egg to form the zygote
       2) 1 nucleus combines with the polar bodies to form the endosperm
     Carpel:  contains the stigma, style, ovary and ovules.
     Flower contains the female and male gametophyte
     Different colors attract different pollinators:
          -white flowers usually are pollinated at night
     Flowers:
          -fly and beetle pollinated flowers smell like dung or rotting flesh
          -bee pollinated flowers are brightly colored:  white, yellow, or blue. have an ultraviolet pattern
          -nectar produced at the base near the ovary.
          -moth and butterfly pollinated flowers have deep nectar tubes.
          -humming bird pollinated flowers are usually red and or yellow