AP Biology
LECTURE NOTES: Chapter 31
Fungi
CHARACTERISTICS OF FUNGI - Fungi are diverse and widespread. They are essential for the well-being
of most terrestrial ecosystems because they break down organic material and recycle vital nutrients.
Fungi are heterotrophs that feed by absorption (do not ingest their food).
• Fungi secrete into their surroundings exoenzymes that break down complex molecules and then absorb the remaining
smaller compounds
• Fungi exhibit many diverse lifestyles
–
Decomposers
–
Parasites
–
Mutualistic symbionts
FIGURE 31.1 & 31.2 - Extensive surface area and rapid growth adapt fungi for absorptive nutrition.
Except for yeasts, ALL fungi are multi-cellular and composed of tiny filaments called hyphae.
• The bodies of multicellular fungi are composed of many hyphae tangled together into a thick mass called a mycelium.
• The mycelium is well suited to absorb food.
• The fruiting body is a reproductive structure that develops from a mycelium that grows below the surface of the ground.
Most fungi have cell walls made of chitin. Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell
movement of materials:
• Coenocytic fungi lack septa
• Some unique fungi have specialized hyphae that allow them to penetrate the tissues of their host
Mycorrhizae are mutually beneficial relationships between fungi and plant roots
•
A symbiotic associations of plant roots and fungi.
• Fungi increases the surface area of the plants roots. Its presence is often necessary for the growth of many plants.
FIGURE 31.3 - Fungi disperse and reproduce by releasing spores that are produced sexually and asexually.
Fungi produce spores through sexual or asexual life cycles
•
Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually
The sexual life cycle of fungi involves
• Cell fusion, plasmogamy
• Nuclear fusion, karyogamy
• An intervening heterokaryotic stage occurs between plasmogamy and karyogamy in which cells have haploid nuclei from
two parents
• The diploid phase following karyogamy is short-lived and undergoes meiosis, producing haploid spores
Many fungi that can reproduce asexually grow as mold, sometimes on fruit, bread, and other foods
• Other asexual fungi are yeasts that inhabit moist environments which produce by simple cell division
• Many molds and yeasts have no known sexual stage. Mycologists have traditionally called these deuteromycetes, or
imperfect fungi
AP Biology
LECTURE NOTES: Chapter 31
Fungi
FIGURE 31.4 & TABLE 31.1 - Fungi are classified according to their structure and method of reproduction.
The 5 main groups of fungi are:
1. Chytridiomycota (spore fungi)
• Chytrids are unique among fungi in having flagellated spores, called zoospores
2.
Zygomycota (common molds)
• Bread molds (ex. Rhizopus stolonifer – black bread mold)
• 3 Types of Hyphae:
 Stolons: Stem like hyphae - run along top of food source
 Rhizoids: Root like hyphae – Penetrate & release digestive enzymes, absorb organic matter
 Sporangiophores : hyphae that push up in air…release spores into the air
3.
Ascomycota (sac fungi)
• Club fungi, yeasts
• The phylum Ascomycota is named for the ascus, a reproductive structure that contains spores.
• Ascomycetes are the largest phyum in the kingdom Fungi
• Some are large and some are microscopic.
• Examples: cup fungi (large) and yeasts (microscopic).
 yeasts are unicellular fungi that have only an asexual life cycle
4.
Basidiomycota (club fungi – common mushrooms)
• The phylum Basidiomycota gets its name from a specialized reproductive structure (called a basidium) that
resembles a club.
• Fruiting bodies are the visible mushrooms
• Produced by vast underground networks of mycelium (bundles of hyphae) when ready to reproduce
 Gills – part on mushroom which contain Basidia
 Basidia have 2 nuclei fuse to make 2N zygote cell
 Zygote undergoes meiosis making Basidiospores which are scattered
 Mating types (+) and (-) can fuse sexually to make secondary mycelium network
5.
Deuteromycota (imperfect fungi)
• Deuteromycota is an extremely varied phylum composed of those fungi that are not placed in other phyla.
• The term imperfect implies that these fungi do not appear to have sexual reproduction.
• Ex: Penicillium notatum – the source of antibiotic penicillin.
FIGURE 31.20 & 31.21 - Though we rarely notice, fungi are all around us as major forces in the dynamics of
all ecosystems. Ecosystems depend on fungi as decomposers and symbionts.
Fungi are found in every ecosystem, where they recycle nutrients by breaking down the bodies and wastes of other organisms.
• Without decay, the energy-rich compounds that organisms accumulate during their lifetime would be lost forever.
• Fungi have a powerful impact on ecosystems and human welfare
• Fungi are well adapted as decomposers of organic material
– Performing essential recycling of chemical elements between the living and nonliving world
• Fungi form symbiotic relationships with
– Plants, algae, and animals
• Some fungi share their digestive services with animals
– Helping break down plant material in the guts of cows and other grazing mammals
AP Biology
LECTURE NOTES: Chapter 31
Fungi
Fungi are heterotrophic decomposers. ALL FUNGI ARE HETEROTROPHS – BUT THEY OBTAIN NUTRIENTS IN VARIOUS
WAYS:
– Many are saprobes, organisms that obtain food from decaying organic matter.
– Some are parasites which harm other organisms.
– Some are symbionts that live in close and mutually beneficial association with other species.
Saprobes – fungi that obtain food by breaking down dead and decaying orgs
– Can be decomposers – good for nutrient cycle
– Earth needs this to maintain life!
– Can be “predators” - some fungi poison and decompose worms which feed on them
Symbiotic Relationships with Fungi:
• Lichen: symbiosis between fungus and photosynthetic green algae or bacteria
– Photosynthetic organism– provides the food (sugar)
– Fungus provides nutrients and minerals
– The lichen break down the bare rock, allowing other plants to grow (pioneer species)
–
Mycorrhizae : symbiosis of a plant root and fungi
– Fungus increases the surface area of plant root and provides plant with water, minerals
– Plant Provides fungus with photosynthetic food
– Fungal presence is often necessary for the growth of many plants
Some fungi produce antibiotics – Penicillium makes penicillin (discovered by Alexander Fleming).
Fungi & Disease: Some Fungi are Pathogenic
– Plant diseases – “Rusts”, Root Rot
– Animal diseases - Ringworm, Yeast infections, Athlete’s Foot