Lecture 14: Fungi

Question 1

What are fungi?

Answer 1

• Eukaryotes that are more closelyl related to animals than plants
• Decomposers and symbionts
• Frequently mutualistic symbiosis

Question 2

Why are fungi important?

Answer 2

• fungal mutualisms are very important for plants to obtain nutrients and protect plants from herbivores
• animals participate in fungual mutualisms as well
• nutrient cycling

Question 3

Why do people care about fungi?

Answer 3

1. disease
2. essential for crop growth
3. important in crop spoilage
4. food source
5. antibiotics
6. bread, beer, cheese, etc.
7. industrial enzymes

Question 4

What evidence proves fungi are more closely related to animals than land plants?

Answer 4

• Fungal infections in humans are more difficult to treat than bacterial infections
• Key traits linking animals and fungi include:
  1. DNA sequence data
  2. both synthesize chitin
  3. Flagella are similar
  4. Both store flucose as glycogen

Question 5

What are the relationships among the major fungal groups?

Answer 5

1. Glomeromycota is monophyletic
2. Basidiomycetes (club fungi) are monophyletic
3. Ascomycetes (sac fungi) are monophyletic
4. Basidiomycota and ascomycota form a monophyletic group (they both form septate hyphae and large “fruiting” structures
5. Sister group to fungi comprises animals plus choanoflagellates

Question 6

What are the two growth forms of fungi?

Answer 6

1. Single celled yeasts
2. Multicellular, filamentous mycelia

Question 7

What are the advantages and disadvantages of mycelia being made of hyphae?

Answer 7

Advantages ->
- Fungi have highest surface area to volume ratio of all multicellular organisms
- Nutrient absorption is extremely efficient

Disadvantages ->
- Prone to drying out
- More abundant in moist environments
- reproductive spores are resistant to drying out and can endure dry periods then germinate

Question 8

What does it mean that all mycelia are dynamic?

Answer 8

They constantly grow in the direction of food sources and die back in areas where food is running out

Mycelia are an adaptation that supports external digestion and the absorptive lifestyle of fungi

Question 9

What are the reproductive structures of fungi?
What divides the hyphae into compartments?

Answer 9

Fungi produce dense, fleshy reproductive structures

The hyphae are separated by septa. Pores allow materials to flow between compartments.

Question 10

What is coenocytic?

Answer 10

Coenocytic means that they lack septa (fungi).
- Many nuclei are scattered throughout the mycelium
- Nutrients can move rapidly through septa pores or through coenocytic fungi from uptake to growth areas

Question 11

What are the key stages of the chytrid life cycle?

Answer 11

1. Haploid adults from gametangia (mitosis produces swimming gametes)
2. Gametes fuse to form a diploid zygote
3. The zygote grows into a diploid sporophyte
4. Haploid spores, which disperse by swimming, are produced by meiosis inside the sporophyte’s sporangium

There is no heterokaryotic stages

Gametes (sexual) and spores (asexual) have flagella. The only known motile fungal cells.

Question 12

How do zygomycetes reproduce?

Question 13

What is zygosporangia?

Answer 13

Zygosporangia are distinctive spore-producing structures of zygomycetes
- They are formed from fusion of cells from joined-together haploid hyphae from two individuals

Question 14

How do basidiomycetes reproduce?

Answer 14

• Basidiomycetes produce mushrooms as their sexual reproductive structures
• All basidiomycete reproductive structures originate from the dikaryotic hyphae of mated individuals

• The club-like, spore-producing cells, called basidia form at the ends of dikaryotic hyphae
• Karyogamy occurs within the basidia

Question 15

What are basidia?

Answer 15

Basidia are formed by basidiomycetes. They are specialized club-like cells at the ends of hyphae.
Each basidium produces four spores.

Question 16

How do ascomycetes reproduce?

Answer 16

• Hyphae from different mating types fuse
• Short dikaryotic hypha with cells containing two nuclei emerges
• After karyogamy, meiosis and one round of mitosis results in the production of 8 haploid spores
• When the ascus matures, spores inside are forcibly ejected

Question 17

What are asci?

Answer 17

Asci are reproductive sac-like cells at the ends of hyphae produces by ascomycetes.
Each ascus produces 8 spores.

Question 18

What themes occur in the diversification of fungi? (are similar)

Answer 18

• All fungi absorb food from their surroundings
• Evolution of novel methods for absorbing nutrients from a wide array of food sources drove the diversification of fungi

Question 19

What are the 3 types of symbiosis?

Answer 19

1. Mutualism
2. Parasitism
3. Commensalism

Question 20

What are ectomycorrhizal fungi (EMF)?

Answer 20

• Found on many tree species in temperate regions
• Form a dense network of hyphae that cover plant roots and extend into soil but do not enter root cells
• EMF hyphae penetrate decaying material and release peptidases

-Peptidases cleave proteins, releasing amino acids that the hyphae transport to spaces between plant root cells
- Emf also provide phosphate ions to the host plant and receive sugars in return

Question 21

What are arbuscular mycorrhizal fungi (AMF)?

Answer 21

• Hyphae grow into the cells of root tissue
• Hyphae inside the plant cell wall are an adaptation that increases surface area for exchange of molecules between fungi and host
• Hyphae form a pipeline extending from inside plant roots into the soil well beyond the root

Question 22

What are endophytes?

Answer 22

Endophytes are organisms that live between and within plant cells.
- They live in close association with roots or aboveground itssues of land plants

• Some increase drought tolerance of their host plants
• some produce compounds that benefit plants by killing herbivores
• Receive benefits by absorbing sugars from plants

Question 23

What adaptations make fungi such effective decomposers?

Answer 23

• Given enough time, fungi can turn trees into soft soils
• Large surface area of mycelium makes nutrient absorption exceptionally efficient
• Saprophytic fungi can grow toward the dead tissues that supply their food

Question 24

What is extra cellular digestion?

Answer 24

Fungi must digest their food before they can absorb it, so they perform extracellular digestion.
- Digestion takes place outside the organism
- Simple compounds result from enzymatic action that are absorbed by hyphae
- The two most abundant organic molecules on earth are digested by fungi: Lignin and Cellulose

Question 25

What are saprophytes?

Answer 25

Saprophytes are fungi that digest dead plant material. They help cycle carbons through terrestrial systems.
- Saprophytic fungi connect the two components of the carbon cycle: fixation of carbon and release of CO2

Without fungi, a lot of carbon would be locked away in dead plant matter

Question 26

What are saprophytes?

Answer 26

Saprophytes are fungi that digest dead plant material. They help cycle carbons through terrestrial systems.
- Saprophytic fungi connect the two components of the carbon cycle: fixation of carbon and release of CO2

Without fungi, a lot of carbon would be locked away in dead plant matter

Question 27

How do saprophytic fungi break down lignin and cellulose?

Answer 27

Saprophytic fungi use lignin peroxidase to break down lignin and expose cellulose, but they can’t live on lignin alone.

Fungi secrete cellulases into the extracellular environment and convert cellulose into glucose that can be absorbed and used as food.