the hypha and the mycelium

Question 1

determinate multicellularity

Answer 1

• strict body plan (eutely)
• genetically hardwired development
  e.g. humans

Question 2

indeterminate multicellularity

Answer 2

• developmentally plastic
• can adapt growth to respond to environment
• important in sessile organisms such as plants and fungi
• modular growth

Question 3

the hypha

Answer 3

• basic growth unit of fungi
• apical growth is driven by osmotic pressure from the uptake of nutrients
• cytoplasm flows towards the tip and the cell wall stretches

Question 4

anastomoses

Answer 4

• fusion of hyphae, allows for radial communication across the colony

Question 5

AVC

Answer 5

• apical vesicular complex, the hyphal tip
• spitzenkorper = organisational centre, joins to cytoskeleton and controls movement of vesicles
• vesicles containing cell wall building blocks brought to tip by microfibrils
• lots of mitochondria due to high energy demand

Question 6

glucans

Answer 6

• amorphous branches sugar polymers
• packs between chitin in cell wall
• enhances strength of chitin
• protection against bending

Question 7

chitin

Answer 7

• amino sugar similar to cellulose
• high tensile strength
• N-acetylglucosamine subunits
• made by chitin synthase
• woven fibres

Question 8

melanin

Answer 8

• phenolics and oxygen
• insoluble
• pigmented
• hydrophobic
• insulates internal mycelia to stop them from absorbing nutrients, as nutrients are depleted within the mycelial network

Question 9

hydrophobins

Answer 9

• small protein
• self-assembling waterproof monolayer
• diffuses away when growing in substrate
• gives fungi the ability to form aerial hyphae

Question 10

cell wall expansion, Bartnicki-Garcia Balanced Lysis model

Answer 10

• vesicles containing lytic enzymes like chitinase break cell wall
• cell wall expands
• vesicles containing chitin and glucan subunits/precursors
• new parts of cell wall rebuilt by synthase enzymes

Question 11

septa

Answer 11

• ingrowths of the cell wall (contain lots of chitin) that act as valves controlling the flow of materials within the mycelium
• can close in case of damage to hypha so cytoplasm doesn’t flow out the mycelium

Question 12

simple pore vs dolipore septa

Answer 12

• simple pore septa is ingrowth of cell wall that can be plugged with woronin body
• dolipore septa are more complex, only in Basidiomycetes, nuclei can’t flow between
• probably related to the large body size and lifespan of basidiomycetes

Question 13

hyphal branching

Answer 13

• usually monopodial, branches alternate
• explore environment and grow towards nutrients
• density of branches depends on how nutritious the medium is
• growth rate and diameter decreases from primary to secondary to tertiary hypha

Question 14

why are hyphal branches formed?

Answer 14

• relieves pressure
• friction restricts rate of flow and creates turbulent flow from friction with the sides of the hypha
• new AVC often formed where there is turbulent flow, wall softens to allows second branch to grow

Question 15

tropic responses of hypha

Answer 15

• chemotropism, towards oxygen and nutrients
• phototropism, towards light, usually fruiting body
• changes in apex direction, branch frequency and branch angle

Question 16

yeast growth, budding

Answer 16

• daughter cell ‘buds’ off mother cell
• nuclear division then cell division
• can leave bud scars on mother cell

Question 17

yeast vs mycelial growth

Answer 17

• yeast has non-polar growth, mycelia have polar (directional) growth
• yeast grows on liquid or on a surface, mycelial grow on an interface and penetrate the surface
• yeast are mobile in liquid, mycelia are sessile, are stuck to substrate
• yeast have a lower SA:V, mycelia have elongated cells so a high SA:V

Question 18

yeast, mycelial dimorphism

Answer 18

• some yeast species such as candida albicans can be both body forms
• mother and daughter cells don’t detach, gain or polar growth
• chain of cells can then branch
• sometimes limited flow of cytoplasm between cells

Question 19

mycelial dimorphism, Candida albicans

Answer 19

• live on mucous membranes
• grows as a mycelium then yeast cells bud off ends of hyphae to spread down gut and colonise more areas

Question 20

the mycelium

Answer 20

• functionally coenocytic (hyphae only joined by septa)
• can communicate via cytoplasm
• system driven by osmotic pressure
• hyphae explore the environment in search of nutrients

Question 21

fairy rings

Answer 21

• originated from 2 spores meeting in centre of ring then outward growth
• mushrooms usually above biggest density of mycelium