Lichens Flashcards
1
Q
What are lichens?
A
- symbiotic association of several Kingdoms
- have emergent properties resulting from this association
- evolved independently
2
Q
What are the photosynthetic partners in lichens?
A
- usually unicellular or filamentous green algae
- less commonly they are cyanobacteria
- both fix atmospheric nitrogen (N2)
3
Q
General structure of lichens:
A
- fungal hyphae provides most of the mass and provides its overall shape (medulla and cortex)
- algal component occupies inner layer below fungal surface
4
Q
What are the reproductive part of lichens and ascomycetes?
A
- ascomycetes in sac fungi, produce ascocarp
- in lichens it is the apothecium that is a cup shaped, spore producing structure formed by fungal compenent of lichens
5
Q
Asexual reproduction in lichens:
A
- soredia = granular or powdery asexual reproductive structures
- comprised of fungal hyphae and algal cells produced on the thallus where the cortex ruptured
- isidia = asexual reproductive structures
- small peg shaped structure produced by upper cortex of thallus
6
Q
What is the structure below referring to?
A
Soredia
7
Q
What is the symbiosis relationship in lichens?
A
- algae provides fungus with food by ‘leaking’ carbohydrates
- cyanobacteria provide organic nitrogen through N2fixation
- the fungus provides suitable habitat for algae and cyanobacteria growth
- by retaining water and minerals
- facilitating gas exchange
- protection from UV
- toxic deterrent to herbivores
8
Q
What is the function of lichen acids?
A
- secreted by fungus secondary metabolism
- they block UV
- antimicrobial
- bioaccumulators of minerals
9
Q
Why are lichens important?
A
- important pioneers on recently exposed mineral soil and rock surfaces
- lichen acids penetrate the outer crystals of rocks and help break down the rock
- facilitates soil-trapping and starts primary succession process
- some nitrogen-fixing lichens add organic nitrogen to ecosystems
10
Q
Tolerance to cold and hot climates:
A
Cold habitat:
- reindeer lichen (Cladonia rangiferina) grow as carpet and provide winter food for caribou and reindeer in the arctic tundra
Dry habitat:
- lichens absorb water quickly for fog or rain
Arid habitat:
- lichens rapidly dehydrate and stop photosynthesis
- lichens grow more slowly
11
Q
What are lichens bioindicators for?
A
- air quality
- they can retain contaminants, like heavy metals
- sensitive to air pollution (NOX and SOX) and their decrease = early warning to deteriorating air quality
- some lichens are nitrophilous and increase in areas where NH3 is sprayed as fertilizer
12
Q
What are the lichen growth forms?
A
- foliose
- crustose
- fruticose
- squamulose
13
Q
What is foliose?
A
- growth form of lichen
- has lower cortex and usually loosely attached by rhizines
- can be attached by umbilicule cord = umbilicate lichens at a central point
14
Q
What is crustose?
A
- lichen growth form where the thallus appears as smear of paint since entire lower surface is completely attached to substrate
- lacks a lower cortex and rhizines
- grow tightly attached to rocks, trees or soils and are hard to remove without damaging substrate beneath
15
Q
What is fruticose?
A
- lichen growth form resembling mini shrubs growing upward or hanging down in strands
- often attached at a single point
- they are often round in cross section = terete
- most are multi branched
16
Q
What is squamulose?
A
- have scale like lobes called squamules, usually small and overlapping
- squamules that form thallus also occur on erect structures called podetia (apothecia at top of podetia)
17
Q
Identify the lichen growth forms below:
A
- there is fruticose, foliose, crustose
