• The fungi are eukaryotic heterotrophs that digest food externally and absorb the the digest materials through their body walls.
• Like plants, their cells have walls, but these walls are made of chitin, not cellulose.
• Fungi, including molds and mushrooms are multicellular, yeasts are unicellular fungi, but this is believed to be a derived state.
• The "conduct their day-to-day" business as a structure called a mycelium, that is composed of single strands called hyphae. It is the mycelium and its associated hyphae that exude hydrolytic enzymes, the digested molecules are absorbed by the hyphae.
  

  The fungi are able to digest cellulose, which makes them important decomposers; and plant "associates."
  

  1. Mycorhizzae: grow into associated root tissue.
  2. Lichens: an association of fungal mycelia and unicellular green algae.
  3. Fungal dieases of plants: Smuts; Rusts; Dutch Elm Diease.

      

Fungus Sex is stranger than truth.

• A mushroom is dikaryotic. Each cell contains two haploid nuclei!
• Within certain cells of the mushroom the two nuclei fuse forming a single diploid cell: a zygote!
• The zygote immediately ungoes meiosis to produce haploid spores.
• The haploid spores develop into haploid mycelia, and go about their fungal business.
• When compatible haploid hyphae meet they fuse, producing cells that grow into a dikaryotic mycelium.
• The dikaryotic mycelia produce "fruiting bodies" (mushrooms and similar structures) in appropriate conditions.

Algae vs. Plants

• Historically, all the photosynthesizers were called "plants."
• Algae (photosynthetic protists) can depend of water for

   

  1. Support: water is dense and can support an alga's body.

     Terrestrial photosynthesizers need to have "skeletal support." A plant's skeleton may be woody or hydrostatic, or both.

  2. Transport: water is a great solvent and algae can take nutrients directly form the water, and remove wastes to the water.

     Terrestrial photosynthesizers need specialized transport systems; perhaps specialized for liquid and gas exchange.

     Liquid transport within vascular plants occurs via two specialized tissues:
     

     • Xylem: conduits of "dead cells" that deliver water and nutrients from the roots.
     • Phloem conduits of living tissue that distribute the products of photosynthesis throughout the plant.
  3. A medium for gamete transport: In water algae can simple release the flagellated gametes, and they can "swim" to their destinations.

     Terrestrial photosynthesizer need mechanisms of transport gamete around, AND a mechanism to keep them from drying out:

     A key feature of plants is a structure called the gametangium (or gamete jar), that protects gametes from then environment.

• Life is wet gooey business; algae have no problem with drying out

  Terrestrial photosynthesizers need protection from drying out: a cuticle.

• Algae only need to stay in place; but plants need to anchor themselves and extract resources from the soil. That is, roots are different from holdfasts.

The four main plant groups

• Plants share many traits with alga: cell walls, plate formation during mitosis, chlorophyll, etc.

  The "key" innovations that allowed the "invasion" of land seem to have been a "cuticle" and a gametangium.

• The bryophytes or mosses; low growing non-vascular plants, characteristic of wet places. Like algae they have flagellated sperm.

  True vascular structures (xylem and phloem) was an important "innovation" that allowed plants to "get up off the ground", and move to dryer places.

• Seedless Vascular Plants (the ferns). These have well-develop roots and rigid stems. They are largely wet-habitat organism, and have flagellated sperm.

  Seeds are important for two reasons. Seed formation mechanisms overcome the need to for "wet" sites of fertilziation; and seeds (pre-packaged) embryos are wonderful agents of dispersal.

• Gymnosperms: the naked seeded plants (conifers, a few kinky things). Do not have flagellated sperm.
• Angiosperms: the "seeds in jar" plants. These are the flowering and fruiting plants we a most familar with; seeds develop within an ovary. They are closely tied with animals; flowers are adapted to insect pollinators, and fruits are adapted for animal dispersal.

The alternation of generations: a "primitive" plant feature

• Diploid animals reproduce sexually by produce single-celled haploid gametes. Direct union of these haploid gametes leads to new diploid indivdual. Normal, right?
• Plants appear to have inherited the alternation of generations from the multicellular green algae.

  In this system: A diploid sporophyte produces haploid spores via meiosis; the haploid spores develop into a haploid gametophyte; Gametophytes produce gametes via mitosis; the union of gametes produces a new sporophyte.

• Review of the alternation of generations in mosses, ferns, gymnosperms and angiosperms.

   

  1. In mosses, the gametophyte is dominant. Sporophytes develop "parasitically" on gametophytes from zygotes fertilized in situ.
  2. In ferns, the sporophyte is dominant. The gametophytic resembles an isolated heart-shaped leaf. Sperm swim to female gametangia; sporophyte grows out of gametophyte.
     
     In the seeds plants the gametophyte is dramatically reduced, and system is superficially "animal-like." There is a clear distinction between male and female gametophytes.
  3. Gymnosperms, the sporophyte is dominant. Male cones produce haploid spores by meiosis; the spore immediately developd into the gametophyte (we call it pollen). Similarly, within female cones haploid spores are produced via meosis; the spores develop into a female gametophyte within in turn produces eggs.
  4. The pattern is nearly identical for angiosperms.
  5. What's the difference between this and the animal system?
     
     • It's really weird.
     • In animals the "instant" a haploid cell exists, its a gamete; but in the alternation of generaion haploids undergo further mitosis to produce gametes; and specialized haploid cells may exist that do not produce gametes.

Information provided by: http://niko.unl.edu