Biological Foundations 112, Lecture 23

Fungi I

Chapter 28, pages 573-588
Basic Botany-2 0:00-9:35
Five Kingdoms-3 0:00-7:27

I.   Characteristics of Kingdom Fungi

     A.   Lack chlorophyll and thus are heterotrophic

            1.   Parasite - lives at the expense of another organism, the host

                  a.   Pathogenic - causes the weakening of the host

                  b.   Obligate - must live as a parasite on a particular host in order to                        

                  c.   Facultative - prefers a particular host but can still live as a saprophyte

            2.   Saprophyte - lives off of dead or decaying organic matter

                  a.   Obligate - must live as a saprophyte

                  b.   Facultative - prefers to live as a saprophyte but can also live as a                      

     B.   General structure

            1.   Hyphae - individual filaments

                  a.   Septate - filaments contain cross walls with one nucleus per cell

                  b.   Nonseptate or coenocytic - filaments that contain no crosswalls and                
                                                                     thus are multinucleated

                  c.   Septa - name given to cell cross walls in a filament

            2.   Mycelium - vegetative mass of hyphae or fungus plant body

            3.   Haustorium - special absorptive tip of a hypha that penetrates the cell wall into        
                                         the center of the cell and absorbs nourishment directly out of the        

            4.   Cell walls are composed of cellulose and chitin

     C.   Types of reproduction

            1.   Types of asexual reproduction

                  a.   Mitosis - to produce new cells or nuclei

                  b.   Fragmentation

                  c.   Zoospores - motile spores that can be haploid or diploid

                        (1)  Produced in zoosporangia

                        (2)  Sporangiophores are stalks on which sporangia stand

                  d.   Chlamydospores

                        (1)  Resistant spores with heavy, thick resistant walls that form around each cell  
                               and a septate hypha

                        (2)  In coenocytic filaments septa form first and then the resistant walls form as    
                              described above

                  e.   Conidia

                        (1)  Packages of zoospores

                        (2)  How they are formed

                              (a)  End cells of tall long hyphae (conidiophores) round up and separate      
                                     from the parent hypha

                              (b)  The round spheres that separate are called conidia

                              (c)  When the conidia find suitable conditions they rupture and release many  

                              (d)  The zoospores swim for a bit and then settle down and encyst

            2.   Types of sexual reproduction

                  a.   Heterogamy

                  b.   Isogamy

                  c.   Dikaryon - n + n condition

                        (1)  Plasmogamy occurs when the gametes unite and karyogamy occurs just    
                              before meiosis

                        (2)  Two haploid gametes unite to produce n = n cells (dikaryon condition)

                        (3)  Dikaryon cells reproduce themselves in large quantities as filaments

                        (4)  In regions where sporangia are formed, dikaryon cells undergo karyogamy  
                               and then meiosis immediately thereafter

                  d.   Reproductive compatibility

                        (1)  Homothallic

                               (a)  Self-compatible

                               (b)  Plasmogamy and karyogamy occur between reproductive structures on
                                      the same thallus or within the same strain

                               (c)  Allows self-fertilization

                        (2)  Heterothallic

                               (a)  Self-sterile and other-compatible

                               (b)  Requires the presence of a separate thallus or strain bearing a                
                                     compatible mating structure before fertilization can occur

                               (c)  Does not allow self-fertilization

II.  Classification of Kingdom Fungi

      A.   Based on:

             1.   Mycelium structure

             2.   Spore type

             3.   Events in the life cycle

      B.   Four Divisions

             1.   Oomycophyta - egg fungi - produces oospores and is coenocytic

             2.   Zygomycophyta - zygote fungi - produces zygospores and is coenocytic

             3.   Ascomycophyta - sac fungi - produces 8 ascospores in a sac and is septate

             4.   Basidiomycophyta - club fungi - produces 4 basidiospores on a basidium and is    

             5.   Deutromycophyta - imperfect fungi

                   a.   These fungi are present in nature but we don't know enough about their life cycle
                         to assign them to the proper division

                   b.  Thus, we give them a temporary name based on what we do know about them  
                        so as to be able to refer to them

                   c.   This temporary name we call a form genus

                   d.   When we have demonstrated the full life cycle of the fungus, it is then named      
                         and assigned to the proper division

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