5. The Fungi Flashcards
1
Q
Describe fungi. 6
A
- 80 000 species identified out of estimated 1.5 million. This is probably an underestimate, as one paper estimated 10M
- Organoheterotrophs. Use organic molecules as an energy source. Hydrolytic enzymes breakdown polymers outside of the cell eg cellulose
Starch
Proteins
Lipids - Have a chitin cell wall
- Invaded the land with plants 430M yrs ago, some of the earliest plants show fungi associations with roots
- Largely haploid and aerobic
- Originally aquatic
2
Q
How do fungi fit into the tree of life? 2
A
- Opisthokonts led to metazoa, including animals and fungi
2. Although this was previously thought false, fungi are more closely related to animals than plants
3
Q
Describe the cellular structure and reproduction of fungi.6
A
- Simple life cycle, either split by asexual or can carry out sexual reproduction
- Most are filamentous, which branch asexually from hyphae. Unicellular yeasts have a sexual life cycle, too.
- Dimorphism fungi can grow in both ways
- Many of these are pathogens
- Eg in the yeast phase, thrush spreads rapidly, then enters the tissue as filamentous
- Dutch elm disease is also dimorphous, it forms a unicellular yeast, which is rapidly distributed by xylem and phloem, then becomes filamentous
4
Q
Describe budding yeast. 3
A
- Daughter cell buds off and grows
- Cells eventually separate
- Some yeast grow filamentously, called mycelial growth
5
Q
Describe filamentous growth of fungi. 6
A
- Spore lands in surface
- Polarised hyphae grow outwards radially
- Branches grow in between so substrate is sufficiently colonised
- No branches, or the fungus would just separate out
- The outside is the growing region
- Hyphae tips secrete enzymes, then digest sugars, amino acids etc.
6
Q
Describe toadstools. 4
A
- Mushrooms/toadstools are the most advanced fungi
- Spread spores
- Most of life cycle is spent as filamentous
- Most fungi don’t do this
7
Q
Describe ‘mould’. 6
A
- A single growth contains 1000-5000 spores per m^3
- If a spore lands on something it can breakdown and utilise, mould grows
- There would be no life without it, a it removed detritus by breakdown
- Powdery mould contains millions of asexual spores usually dispersed by air
- A hyphae fungal colony is an efficient system for breakdown and absorption, a substrate gradient is created
- More nutrients around the outside
8
Q
Describe the process of hyphal growth. 6
A
- Hyphal growth located at tip point and supported by vesicles.
- Transportation of vesicles by Golgi body along actin myosin cytoskeleton to the tip.
- Vesicles contain enzymes for producing new cell wall
- Vesicles fuses with membrane, releases substrate for cell wall growth and chitin
- Moving away from tip, cell wall becomes more rigid and less flexible
- This is driven by osmotic pressure, doesn’t burst due to movement of enzymes
9
Q
Describe hyphal walls. 6
A
- There is an outer wall made of beta 1-3 glycan
- Followed by inner wall of chitin
- Chitin is a polymer of NAG
- It is the main strength building polymer
- This is followed by the plasma membrane
- Not discrete layers, there is mixture and blending of inner and outer walls
10
Q
What are the main divisions of the fungal Kingdom? 5
A
- Chytrids - largely aquatic
- Zygomycetes - associated with plant roots
- Glomeromycetes - associated with grasses
- Ascomycetes - biggest
- Basidiomycetes - mushrooms
11
Q
Describe the chytridomycota group. 5
A
- Aquatic fungi
- Asexual and sexual flagellated spores which swim until they find a suitable surface
- Most primitive fungi (others lack flagellated stage) from which others have evolved
4large thallus from which rhizoids emerge and grow into plants. They contain motile zoospores - Upon reaching a suitable surface, spores attach themselves, lose flagella and invade the tissue
12
Q
What is the relationship between chytridomycota and ruminant animals? 5
A
- Ruminant animals have a modified, chambered stomach
- Anaerobic bacteria, archaea and fungi digest cellulose like and internal fermenter
- These are the only anaerobic fungi
- Digestion pathway: cellulose converted to glucose to fatty acids before absorption
- Ruminant animals include cows
Sheep
Llamas
Deer
Buffalo
Giraffes
Goats
13
Q
Describe the zygomycota. 5
A
- Some cause food spoilage
- Terrestrial with asexual, non motile spores
- They are air dispersed with sporangia which rupture to disperse sporangiospores
- They also have a large, sexual zygospore
- Can produce melanised sexual spores with no male or female, only - and + strains
14
Q
Describe the Ascomycota. 5
A
- Largest and most diverse group
- Produce aerial borne chains of asexual conidiospores, this is their usual method of reproduction
- Also produces ascus(es), which contain 8 sexual ascospores, which are less common
- Group includes many plant pathogens and these responsible for food spoilage - general mould.
- Eg birds nest fungus is small with spores embedded in outer rim, rain splashed distribute the spores
15
Q
Describe the basidiomycota. 6
A
- Most advanced group
- Form visible mushrooms and toadstools
- Usually four sexual basidiospores borne on a basidium, held to it by sterigmata
- Basidia line gills or pores of the mushrooms
- Many form mycorrhizal associations with trees, which is very important for the ecosystem
- 99% of trees have these associations
