Fungi

Question 1

Fungi

Answer 1

monophyletic group of eukaryotic heterotrophs closely related to animals
- cells contain nucleus, mitochondria, complex system of internal membrane
- fungal cells do not have chloroplasts or chlorophyll
- lineage that led to fungi + animals is thought to have diverged from the future-plants lineage during the Proterozoic Eon
- believed to diverge from future-animals lineage near end-Proterozoic
- FUNGI ARE MORE CLOSELY RELATED TO ANIMALS THAN PLANTS
- common ancestor of all fungi was likely fungi, flagellated, and single-celled
- the evolutionary relationship between some groups of fungi are not yet resolved

Question 2

Shared Adaptations/Traits in Fungi

Answer 2

• different species of fungi can be mutualistic, parasitic, or serve as decomposers
• fungi can be multicellular or unicellular and have a wide range of body plans
• all fungi have: heterotrophic eukaryotes, cell walls made up of chitin, and external digestion systems

Question 3

Heterotrophic Eukaryotes

Answer 3

all fungi must use existing organic compounds as a source of carbon

Question 4

Chitin Cell Walls

Answer 4

the cell wall provides structural strength to the fungal body
- chitin is a tough polysaccharide that is also a major component of exoskeletons in other organisms

Question 5

External Digestion

Answer 5

all fungi externally digest food - they excrete digestive enzymes outside of their bodies, and the digested nutrients are then absorbed from the external environment
- fungi do not have internal digestive tracts

Question 6

Morphology

Answer 6

most fungi are multicellular but some are unicellular; some can switch between the two states depending on environmental conditions

Question 7

Unicellular Fungi

Answer 7

reproduce via BUDDING, and the new bud separates from the parent cell to form 2 separate, individual cells

Question 8

Multicellular Fungi

Answer 8

have cells that work together in a body structure called MYCELIUM (plural: mycelia)
- composed of branches of cells (HYPHAE)
- produces reproductive units (SPORES) directly or through a FRUITING BODY

Question 9

Hyphae

Answer 9

long, branching filamentous thread-like structures that look like roots
- composed of individual cells connected end-to-end in a long branching thread
- depending on the species, they can grow on the surface, in soil or decaying material, or on living tissue
- excrete digestive enzymes into the environment and absorb nutrients released by digestion

Question 10

Spores/Fruiting Body

Answer 10

the morphology of the reproductive stage varies across fungal species
- some are visible as mushroom fruiting bodies (mushrooms is the only above ground fruiting body and underground hyphae)
- in other fungi, the reproductive stage is microscopic

Question 11

LIFE CYCLE

Answer 11

some fungi reproduce only asexually but some can reproduce both asexually and sexually via the HAPLONTIC LIFE CYCLE
- the multicellular stage is haploid, and the diploid stage (the fertilized egg) exists as a single cell before undergoing meiosis to produce haploid spores
- in both sexual + asexual reproduction, fungi produce spores that disperse from the parent organism by floating on the wind or attaching to an animal
- the large # of spores released increases the likelihood of landing in an environment that will support growth

Question 12

Vegetative Growth (Asexual Reproduction)

Answer 12

the mycelium (the fungal body composed of hyphae) is HAPLOID; the mycelium germinates via mitosis from a haploid spores
- the haploid mycelium can continue to grow via mitosis or reproducing asexually via BUDDING, FRAGMENTATION, or by PRODUCING ITS OWN HAPLOID SPORES

Question 13

Asexual: Budding

Answer 13

controlled growth of a new cell on the side of an existing cell, which detaches

Question 14

Asexual: Fragmentation

Answer 14

breaking into smaller pieces where each piece can continue growing as an independent organism

Question 15

Asexual: Producing Spores

Answer 15

a fungi can produce its own haploid spores via mitosis which disperse and grow a new haploid mycelia
- spores produced via mitosis are genetically identical to the parent (ASEXUAL REPRODUCTION!)

Question 16

Sexual Reproduction

Answer 16

results from the fusing of cells from two mycelia followed by the production of spores by meiosis
THE PROCESS:
1. Plasmogamy + Heterokaryotic Stage
2. Karyogamy
3. Meiosis
4. Germination

Question 17

Sexual: Plasmogamy + Heterokaryotic Stage

Answer 17

to initiate sexual reproduction, haploid cells from two different mycelium fuse together, sharing their cytoplasm (PLASMOGAMY)
- their nuclei DO NOT FURE and remain independent in a structure that is “HETEROKARYOTIC”
- depending on the species, the heterokaryon grows into a fruiting body or remains microscopic

Question 18

Sexual: Karyogamy

Answer 18

at this stage, 2 nuclei within a heterokaryotic cell fuse to form a diploid nucleus
- this stage does not grow any new cells or tissue

Question 19

Sexual: Meiosis

Answer 19

the diploid nucleus undergoes meiosis to produce 4 haploid spores (these spores are a product of sexual reproduction as a result form the meiotic cell division of a diploid cell)

Question 20

Sexual: Germination

Answer 20

the meiotically produced spores are dispersed by wind or animal to a new environment, where they can germinate into a new mycelium + enter a new cycle of growth (sexual or asexual)

Question 21

Common Fungal Metabolism Traits

Answer 21

Because of their varied metabolic pathways (listed below) humans use fungi for applications like producing food, antibiotics, medicine, and tools in bioremediation:
1. External Digestion
2. Decomposers
3. Mutualists
4. Parasites
5. Predators

Question 22

Decomposers

Answer 22

most fungi are decomposers - they derive nutrients from decaying/dead organic material
- fungal decomposers are also called SAPROPHYTIC FUNGI
- fungal digestive enzymes break down insoluble polysaccharides (cellulose + lignin) into absorbable glucose molecules
- fungi decompose matter to release larger, vital elements such as nitrogen and phosphorus
- within decomposers, these nutrients would remain fixed within dead organisms and unavailable for living things

Question 23

Mutualists

Answer 23

some fungi form mutualistic relationships with plants, where fungi trade water and nutrients for exchange for plant sugars
- MYCORRHIZAL FUNGI (~80-90% of plants rely on them for growth)

Question 24

Parasites

Answer 24

some fungi are parasitic, infecting either plants or animals

Question 25

Predators

Answer 25

in environments pour in NITROGEN, some fungi act as predators, trapping small animals like nematodes via a constricting ring within their hyphae that functions as a noose

Question 26

Symbiosis

Answer 26

the ecological interaction between two organisms that live together

Question 27

Mutualistic Symbiosis

Answer 27

a symbiotic relationship in which both members of the association benefit
- fungi form these associations with many organisms like cyanobacteria, algae, plants, and animals

Question 28

Plants + Fungi

Answer 28

• ~80-90% of plants form mutualistic relationships with fungi via their ROOTS (EX: mycorrhizal fungi) to exposes them to more nutrients, nitrogen, and water from decaying organisms in the soil
• in exchange, plants supply the products of photosynthesis (sugars) to fuel the metabolism of fungus

Question 29

Plants + Fungi History

Answer 29

• in EARLY-PALEOZOIC, there way very little soil and most land on Earth was rock; the combined action of early fungi secreting digestive enzymes coupled with erosion slowly created SOIL (plants needed this soil in the future)
• First land plants were Bryophytes, where early fungal associations with these plants helped provide water + nutrients as these plants lacked TRUE ROOTS
• Seedless Vascular Plants that had true roots had selective advantage over bryophytes because they could anchor and extract water. These roots allowed a greater surface area of contact with fungal partners and more mutualistic exchange
• Over time, these interactions led to the evolution of present day mycorrhizae