lecture 19: fungi

Question 1

Morphology of fungi?

Answer 1

Mostly multicellular, some unicellular (yeast), some can change between

Question 2

Cell wall?

Answer 2

Yes, made of CHITIN (unique in fungi)

Question 3

Mode of nutrition?

Answer 3

Chemoheterotrophs —> extracellular digestion and absorptive feeding (release chemicals to break down organic material and then absorb them)

Question 4

Oxygen requirement of fungi?

Answer 4

Mainly aerobic, some yeast are facultative anaerobes

Question 5

Reproduction of fungi?

Answer 5

Asexually or sexually (using spores)

Question 6

Motility?

Answer 6

Not motile, but tropism (grow in direction of food) & dispersed by spores

Question 7

Unique characteristics of fungi?

Answer 7

1. Body structures made of a network of thread-like filaments of cells called HYPHAE
2. Cell walls made of chitin
3. After mating, cells are heterokaryotic (contain 2 or more genetically distinct nuclei in one same cell) before fusion of nuiclei
4. Can reproduce sexually, but most do not produce gametes/any flagellated cells

Question 8

Are fungi more closely related to plants of animals? Why?

Answer 8

Before: considered plant-like
Now: actually more closely related to animals —> share recent common ancestor
- DNA sequence data
- Some animals and all fungi synthesize chitin
- Animal flagella and flagella in some fungi = similar in structure and function
- Both store glucose as glycogen

Question 9

Where do you find fungi?

Answer 9

• Moist terrestrial ecosystems (large network of filaments undergound), some aquatic
• Fruiting bodies = aboveground (like mushrooms)

Question 10

2 growth forms/bodies of fungi

Answer 10

1. Yeast: single-celled forms
2. Mycelia: multicellular, filamentous forms

Some fungi can adopt both forms during their lifecycle

Question 11

What is hyphae? Types?

Answer 11

Form vegetative (non-reproductive = spaced out hyphae)) & reproductive structures (dense hyphae) of multicellular fungi

• Septate (divided) hyphae: each filament is separated into cell-like compartments by cross-walls called SEPTA with gaps called PORES that enable materials to flow between compartments
• Coenocytic hyphae: no division between cells —> produced by mitosis without cytokinesis —> multiple nucleus in a cell

Question 12

What is the body of fungi composed of? What does this material give to fungi?

Answer 12

Mycelium: branching networks of very thin hyphae:

• Gives highest surface-area-to-volume ratio —> increases efficiency of absorption
• Allows fungal mycelia to penetrate tiny fissures in soil and absorb water and nutrients that are inaccessible to other organisms

Question 13

Downside of mycelia?

Answer 13

Makes absorption extremely efficient, but makes fungi prone to desiccation —> Higher surface area so more water loss —> Fungi = restricted to moist, underground habitats

Question 14

How does mycelia allow fungi to do?

Answer 14

• Allow fungi to absorb nutrients
• Mycelia = adaptation to the absorptive lifestyle of fungi
• Fungi secrete digestive enzymes & can absorb the products via the mycelium

Question 15

What are spores?

Answer 15

Fundamental reproductive cell in most fungi

• Vehicles of dispersal of gametes
• Produced in huge number in specialized structures during both asexual and sexual reproduction phases
• Can germinate into new mycelia

Question 16

How are fungal life cycles unusual? (3)

Answer 16

1. Body cells = haploid (n), only diploid cell (2n) = short-lived zygotes
2. Can form heterokaryotic cells (contain haploid nuclei from 2 different individuals) during sexual reproduction
3. Most species reproduce sexually, but few produce gametes

Question 17

How are fungi diverse? (2)

Answer 17

1. Different ways to absorb food from environment
2. Different ways to reproduce —> four types of distinctive reproductive structures —> ex: fruiting bodies aboveground —> thick, fleshy structures

Question 18

Ecological roles of fungi (4)

Answer 18

• Important decomposers in terrestrial ecosystems
• Important mutualists with plants and other organisms
• Parasites of plants and animals
• Food for other organism

Question 19

What do fungi do as decomposers? What fungal species is an important decomposer?

Answer 19

• Saprophytic fungi, in terrestrial ecosystems
• Dispersed via spores/grow towards dead tissue to digest & absorb nutrients
• Particularly important in digestion of WOOD
• Produce digestive enzymes that can hydrolyze:
  1. Cellulose: structural polysaccharide in cell walls of plant cells
  2. Lignin: extremely hard to break down, complex structural polymers in cell walls of some plant cells (ex: wood)

Question 20

What is “mycorrhiza”? (FINAL)

Answer 20

Mutualism between fungi and plants

1. Plants provides SUGARS from photosynthesis
2. Fungi provide water & key nutrients from soil (nitrogen and phosphorus nutrients)
   - Roots of virtually every land plant = colonized by mutualistic fungi —> have huge impact on their growth

Question 21

Mutualism between fungi and lichen (FINAL)

Answer 21

Lichen = photosynthetic partner (cyanobacterium or algae)

1. Lichen provides SUGARS
2. Fungi provides protection from desiccation and nutrients that it traps from the air
   - Lichen partners = so dependent on each other that most cannot survive if separated

Question 22

Importance of lichens (3)

Answer 22

1. Lichens = pioneers in barren areas and initiate soil production
2. Primary food source of many animals
3. Used in production of dyes and perfumes

Question 23

How can fungi be parasites?

Answer 23

Cause illness in humans: athlete’s foot, diaper rash, ringworm, vaginitis, pneumonia
- Opportunistic pathogens: become parasites if our immune system is weaker —> fungal infections can be serious in immunocompromised human hosts and cause opportunistic infections

Question 24

Impact on humans?

Answer 24

1. Rot food
2. Cause disease in plants and animals
3. Produce important products
4. Research, medicine, and biotechnology

Question 25

Use of fungal products?

Answer 25

• Reproductive structures = source of food (mushrooms)

- Source of antibiotics and other products

Question 26

Fungi in research?

Answer 26

• Saccharomyces cerevisiae = Model organism to study eukaryotic cells in molecular biology
• Yeast = unicellular and easy to culture and manipulate in lab (like bacteria)
• Yeast = contributed to our current understanding of cell cycle, gene expression and cell communication in eukaryotic cells

Question 27

Fungi in biotechnology?

Answer 27

• Saccharomyces cerevisiae (Baker’s yeast) = used for fermentation and use of its byproducts in making of food and drinks (alcohol, chocolate, blue cheese)