Chapter 20 - Chapter 20 The Diversity of Fungi Key Features...

Chapter 20:
The Diversity of Fungi

1. Fungi Obtain Their Nutrients
from Other Organisms
2. Fungi Propagate by Spores
3. Most Fungi Can Reproduce
Both Sexually and Asexually
Key Features of Fungi

Body Structure
•
Most fungi are multi cellular
•
Cells are surrounded by cell walls
composed of chitin, a nitrogen-containing
polysaccharide
•
Body of almost all fungi is a mycelium an
interwoven mass of threadlike filaments
called hyphae (singular, hypha)
•
Figure 20-1(a,b),p. 388 illustrates the
filamentous body of a fungus

hyphae

Hyphae
•
Hyphae of most species are divided into
many cells by partitions called septa
(singular, septum); each cell possesses one
or more nuclei
–
Pores in the septa allow cytoplasm to stream
from one cell to the next.
•
Hyphae of some fungi lack septa, consisting
of single elongated cells with hundreds or
thousands of nuclei
•
The nuclei of most species are haploid

cell wall
septum
cytoplasm
pore
two haploid
nuclei

Nutrition and Fungal Lifestyles
•
All are heterotrophic (secrete enzymes
outside their bodies and absorb the digested
nutrients)
•
Have diverse lifestyles
–
Fungal decomposers (saprobes) feed on dead
organic material and waste
–
Fungal parasites absorb nutrients from cells of
living hosts and may cause disease
–
Some symbiotic fungi live in mutually beneficial
relationships with other organisms
–
Fungal predators consume living organisms

Fungi Reproduce by Means of
Spores
•
Spores are haploid reproductive cells
capable of developing into an adult fungus
–
Usually produced in large numbers
–
Dispersed by animals on air currents
•
Most fungi can reproduce both sexually
and asexually
•
Both asexual and sexual reproduction
involve the production of spores within
fruiting bodies

Spores being
dispersed
after a drop of
water hits the
fungus

Asexual Reproduction
•
Typically occurs under stable conditions
•
Can occur either by:
–
Fragmentation of the mycelium
–
Asexual spore formation
•
Spores germinate and develop into a new
mycelium by mitosis
•
Results in the rapid production of
genetically identical clones

Sexual Reproduction
•
Typically occurs under conditions of
environmental change or stress
–
Two different hyphae fuse so that the nuclei share
a common cell
–
The different haploid nuclei fuse to form a diploid
zygote
–
Zygote undergoes meiosis to form haploid sexual
spores
–
Spores germinate and develop into a new
mycelium by mitosis
•
Results in the production of genetically
diverse fungal bodies