Lecture 10

Question 1

What is the most common form of sexual reproduction in fungi?

Answer 1

Asexual.

Question 2

What is the general life-cycle of fungi?

Answer 2

1. Spore: small, dormant reproductive structure. Germinates into hypahe
2. Hypahe: long, branching filamentous structure which is the main mode of vegetation growth.
3. Mycellium: collective mass of hyphae which is great for nutrient absorption but bad for water loss.

Question 3

Describe the structure of hyphae.

Answer 3

Cells are surrounded by cell walls and are sometimes divided by internal cross walls called septa- usually perforated to allow movement of organelles and communication between cells.

Question 4

Describe the structure of fungal cell walls.

Answer 4

Chitin microfibrils and protein surrounded by other proteins, a reticulum of mixed glucans and protein and an outer mix of glucans.

Question 5

What is the function of the fungal cell wall?

Answer 5

Maintains cell structure, prevents osmotic lysis, has antigenic properties, regulates interactions with other organisms, melanised for UV protection and is a binding site for enzymes.

Question 6

How do hyphae grow?

Answer 6

Grow from the tip where there is abundant mitochondria. Branching occurs just behind the tip. Vesicles add new sections to the cell walls.

Question 7

How do fungi feed?

Answer 7

They feed on simple sugars, polypeptides and complex carbohydrates which are too big to be absorbed through cell walls. Therefore they are externally digested and the soluble products are absorbed.

Question 8

Describe the process of fungal digestion.

Answer 8

Golgi packages proteins and enzymes into vesicles which are transported along microtubules and actin filaments to the hyphal tip. Vesicles exocytose enzymes into the environment (amylases, lipases, proteases etc.) where they digest organic polymers. Nutrients then absorbed through plasma membrane protein.

Question 9

What allows extension of the hyphal tip?

Answer 9

Water follows nutrients being absorbed into the hyphal tip.

Question 10

What are the 4 zones of fungal colony structure?

Answer 10

1. Edges are the extension zone where hypahe reach out to find fresh nutrients.
2. Productive zone where hyphae are linked by anastomosis into a network to allow communication with itself. There is a net increase in biomass here.
3. Fruiting zone initiates fruiting bodies.
4. Aged zone where hyphae are self-digested and become vacuolated and empty.

Question 11

What are fairy rings?

Answer 11

Where N is released back into the soil at night which promotes the growth of other plants.

Question 12

What does isogamous mean?

Answer 12

When gametes are similar (in most of fungi) so male and female do not apply.

Question 13

What is the difference between homothallic and heterothallic?

Answer 13

Homothallic species can mate with themselves whereas heterothallic species can only mate with isolates of the opposite mating type.

Question 14

Define higher fungi.

Answer 14

Asomycota and Basidiomycota which have separate hypahe and are more advanced.

Question 15

What other groups of fungi are there?

Answer 15

Zygomycota which have no septa between cells and imperfect fungi.

Question 16

How are fungi phyla classified?

Answer 16

By their sexual reproductive structures and their hyphae structures (separated or not).

Question 17

What are the 3 main phyla of fungi?

Answer 17

Basidiomycota, ascomycota, zygomycota.

Question 18

What defines basidiomycota?

Answer 18

35,000 spp. Have basidium, a microscopic spore producing structure each of which produces 4 basidiospores (+ or - type).

Question 19

Describe bio-luminescence.

Answer 19

Luciferin + reductase + luciferase. All peak at night, particularly in tropical rainforests where there is little wind. Suggest they may help aid spore dispersal via animals.

Question 20

Describe reproduction in Basidiomycota.

Answer 20

1. Basidium release spores that land and germinate (if conditions are right) into hyphae (haploid).
2. Hyphae fuse by plasmogamy.
3. Fruting bodies (basidiocarp) develop underground. and the gills on them have hymenium tissue which develops into basidia.
4. Fertilisation occurs in the basidium. Karyogamy (fusing of 2 haploid nuclei).
5. Meiosis: basidiospores are formed and released (haplod).

Question 21

Define plasmogamy.

Answer 21

When the cytoplasm of 2 parent cells fuse without fusing nuclei. Nuclei cohabit a cell. Not haploid or diploid and is unique to fungi.

Question 22

What defines Asomycota?

Answer 22

64,000 spp (largest phylum). Also known as sac fungi as they have ascus which is a microscopic sac like sexual structure in which spores are formed.

Question 23

Describe reproduction in asomycota.

Answer 23

1. Spores are released actively or passively from acrospores.
2. Acrospores germinate and gametagenia sexual structures form from the fungi. There are 2 different types, ascogonium and antheridium.
3. Very fine hyphae called trichohyne emerges from the ascogonium and merges with the antheridium.
4. Nuclei in antheridium migrates into the ascogonium (plasmogamy).
5. Fruiting body (ascocarp) forms including hymenium which develops into asci at the bottom of the cup.
6. Karyogamy occurs in the ascus followed by meiosis and mitosis.

Question 24

What defines zygomycota?

Answer 24

1050 spp. Most primitve conjugating fungi. Lack septa between cells. Molds, plant symbionts, animal pathogens.

Question 25

How does zygomycota reproduce?

Answer 25

1. Hyphae of 2 different mating types grow side by side and produce branches that grow towards each other. 2. Tips of these develop into gametagenia which produce gametes. 3. Undergo plasmogamy to form zygosporangium. 4. Undergo karyogamy fertilisation to form multinucleate zygospore within sporangium.