BIO 104 4/9/96

*The Biosciences Learning Center is now open!*
  New Hours are:
          Monday-Thursday          8:30 am-9:00 pm
          Friday              8:30 am-5:00 pm
          Saturday           10:00 am-5:00 pm
          Sunday              1:00 pm-8:00 pm

Plants
The Life Cycle of a Heterosporous Vascular Plant
SEE FIGURE 28.7
 -heterosporous:  The plant posses both male spores and female spores.
 -homosporous:  The plant posses one kind of spore which has both sex characteristics contained in the spore
     Male spores are known as microspores
     Female spores are known as megaspores
 -Sporophyte may have two types of sporangium:
          1)  microsporangium
          2)  megasporangium
     Microsporangium give rise to the microspore, and the Megasporangium gives rise to the megaspore.  
     The mega and microsporangium are collectively known as the mother cell.
     The mother cell by meiosis give rise to the micro and megaspores.
     Usually only 1 of the 4 megaspores produced will become the egg.
     Microspores give rise to microgametophyte (pollen).  Megaspores give rise to megagametophytes which contain the egg.
     The sperm and egg unite in a process called syngamy that in turn gives rise to the zygote.

Life Cycle of Mosses
SEE FIGURE 28.1
-Mosses are homosporous
-Spores germinate to form the male and female gametophytes.

Structures called antheridium give rise to sperm.
-Sperm, using flagella, swim into the archegonium to fertilize the egg.  The sperm is produced by
mitosis.

-(A 1N spore gives rise to a haploid gametophyte  which gives rise to 1N gametes)

At this point there was a slide presentation on the life cycle of a moss showing both gametophyte
and sporophyte. The sporophyte was the setae and capsule (where Meiosis takes place)


Life Cycle of the Fern
-Ferns are homosporous 

SEE FIGURE 28.2 IN TEXT FOR THE FERN LIFE CYCLE

Process begins with the sporophyte
     -Ferns have rhizome, not roots
     -Ferns posses fronds.
     -On the underside of the frond there are sori (sorus -singular) which are clusters of sporangia)

     -The sporangium releases the spores, which develop into a heart shaped gametophyte.
     -This microscopic gametophyte posses rhizoids.

     Located on the gametophyte:
     1) The female egg producing archegonium
     2) The sperm producing antheridium
     
     The sperm move into the archegonium and fertilize the egg.  The embryo then develops
into a sporophyte.

At this point there was a slide presentation on the life cycle of a Christmas Fern.

     Note:  Spores are a result of Meiosis.

Pine Life Cycle
SEE FIGURE 28.3
     Pollen is the male gametophyte
2 Kinds of cones:
     1)  Ovulate cone
          megaspore mother cell
     2)  Pollen bearing cone
          microspore mother cell
  Megaspore mother cell goes through meiosis:
     Three spores degenerate (similar to an egg with 3 polar bodies).
     One megaspore undergoes mitosis to form the female gametophyte which contains two separate eggs (two archegonia).
     Pollen grain lands on a cone and grows a pollen tube into the archegonium to fertilize one
of the eggs.  
     The zygote develops into the sporophyte embryo within the seed.
     2 years later the cone is ready to drop mature seeds for fertilization.
     The seed contains the sporophyte embryo, which is surrounded by the gametophyte and further encased by old sporophyte tissue.     

     We will begin tomorrow's lecture with a review of the pine life cycle.