General Botany
Lecture Notes
Feb. 12, 2009

 


Today, we covered a few smaller topics, and began our study of algae.


INDIVIDUAL CELL MOVEMENT

Individual eukaryotic cells generally move (or are motile) in one of two ways:

1   amoeboid movement (= like an amoeba, by deforming the cell membrane)

                                OR

2   by means of flagella (singular = flagellum).  Eukaryotic flagella typically have a 9+2 microtubule arrangement, and are is linked to a centriole in the cell.  When flagella are small and short, they often are called cilia.  There are two main types of eukaryotic flagella:  whiplash and tinsel.  (See p.309 in the textbook.)  It is remarkable that eukaryotic flagella all have a similar structure -- it strongly implies that flagella were acquired very early in the evoluaiton of eukaryotic cells.  Obviously, flagella give cells advantages in covering territory, encountering prey, mating, moving from inhospitable environments to more favorable environments, etc.

Depending on whether the environment is aquatic or just moist, motile cells of many organisms can convert from flagellated to amoeboid (by withdrawing the flagellum into the cell), or vice versa.

Why do we bring this up now?   -- because algae and fungi are on the horizon, and often have motile cells.


THEORY OF SERIAL ENDOSYMBIOSIS


THIS IS A SIGNIFICANT BIOLOGICAL THEORY THAT YOU SHOULD KNOW ABOUT. 
The ramifications of this idea are quite far-reaching.

THE THEORY:
       
Ancient prokaryotes were captured by other cells and, in time,
        became integral parts of the cells that had captured them.

        Why? - because having the "captives" gave the larger cells great advantages.

  Endosymbiosis was the probable origin of mitochondria, plastids, possibly flagella
  or, in other words, 
serial endosymbiosis produced the first eukaryotic cells.

      EVIDENCE 
           DNA is similar to prokaryotic DNA, ribosomes are similar to prokaryotic ribosomes,
           size is similar to prokaryotic cells, reproduction is independent of the cell in which
           they "reside".  Endosymbionts even exist today (algal cells inside the cells of coral polyps = zooxanthellae)

This theory was first developed by Mereschkowsky (1905), and later fleshed out by Margulis in the 1980s. For additional reliable details and evidence, you can  follow this link .


TYPES OF SEXUAL FUSION

Check out a summary of this at the bottom of p. 309 in your textbook, and consult the handout distributed in class [on Tues. Feb. 17].




The Algae =

                      anything photosynthetic thats less complex than a plant . . .  
                      simple photosynthesizers.


CHARACTERISTICS OF ALGAE

       -- photosynthetic
       -- basically aquatic (some are terrestrial in moist habitats)
       -- organization is simple (usually) to complex
       -- no embryos                         (old name for non-embryo-forming organisms with cell walls = Thallophytes)
       -- unicellular gametangia
       -- unicellular sporangia
       -- asexual reproduction by fragmentation and/or zoospores [= spores that swim with flagella] is common
       -- ecologically, algae = phytoplankton


The algae are a very diverse group of organisms, some of which are very distantly related to each other, but the term algae is useful from a functional and ecological vierpoint.

Alga is the singular of algae.


SIGNIFICANCE OF ALGAE  -- is coming next . . . and a bunch of algal groups. 
See pp. 298-299 in your textbook.


end of notes for Feb. 12