Lichens

Question 1

Describe the lichen organism

Answer 1

The plant bod of the lichens is called phallus; no differentiation into roots, stems and leaves
- Lichen phallus consists of 2 unrelated components;

Question 2

What are the 3 main layers found in the lichen thallus?

Answer 2

Cortex

Question 3

Describe the composition of the cortex

Answer 3

Mainly composed of fungal hyphae compressed and tightly packed
The surface of the cortex is often covered with a thin homogeneous cuticle
In some cases I.e in followed lichens, there may be a lower cortex below the media which consists of thin and loosely packed fungal hyphae often covered with anchoring strands of hyphae or rootlike structures called rhizines.

Question 4

What is the role of the cortex?

Answer 4

Serves to keep away other organisms
Helps to reduce intensity UV radiation of which may damage the algal cells

Question 5

In what ways are algae benefitting from symbiotic relationship of lichen?

Answer 5

Metasth cells secrete a substance that is unpalatable protecting it from predation?
Cortex keeps away other organisms

Question 6

Describe Haustoria

Answer 6

The algal layer and fungal layer are in close contact due to Haustoria.Haustoria are special food absorbing hyphae;since algae make food by photosynthesis the fungi use Haustoria that penetrate the algal cells to absorb food (beneficial to fungi)

Question 7

In what ways do the fungi benefit from symbiotic relationship in lichen?

Answer 7

They absorb food using Haustoria from algae.

Question 8

Describe medulla of lichen

Answer 8

• medulla has a water holding capacity and functions as the region of water storage.It occurs below the algal layer and consists of loosely packed fungal hyphae

Question 9

Describe fruticose lichens

Answer 9

• thallus may be round or flattened, unbranched or richly branched
• anchored by basal rhizoidal strands found in cortex.

Question 10

Describe the vegetative structures - soredia

Answer 10

• the vegetative structures are found in the dorsal or ventral surface of the thallus
• soredia (singular ; soredium) are clumps of algal cells …
• soredia are the main propagules used by lichen for reproduction.
• when they land on favourable environment after detaching from lichen, they divide mitoticalky to form new lichen thallus

Question 11

Describe the Isidia vegetative structures

Answer 11

• composed of algal and fungal tissues
• are cylindrical finger-like protruberances
• one of main propagules used in reproduction…
  -…

Question 12

Describe Cyphellae vegetative structures

Answer 12

• large round pits in lower cortex (foliose genus)
• thought to take part in gaseous exchange and aeration of
• no medullary hyphae protrude into depressions

Question 13

Describe ps….. vegetative structures

Answer 13

• smaller depressions compared to cyphallae
• can occur on lower or upper cortex
• gas exchange and aeration of thallus
• medulla hyphae protrude

Question 14

Describe Cephalodia vegetative structures

Answer 14

• are purgrowths of the thallus containing foreign alga different from the host phycobiont
• is a foreign alga joining already formed symbiotic relationship
• common in fruticose liche s

Question 15

Describe Cephalodia vegetative structures

Answer 15

• are purgrowths of the thallus containing foreign alga different from the host phycobiont
• is a foreign alga joining already formed symbiotic relationship
• common in fruticose lichens

Question 16

Describe the main fruiting bodies of lichens - Perithecia

Answer 16

• Perithecia ; flask-shaped structure that can be immersed within a thallus or sessile on it
  Mature spores are usually released through a pore at the top of the perithecium called ostiole
  Fertile layer called
  The sterile layer (dont have spores)consists of structures called paraphyses hamathecium.These structures aid in the dispersal of spores
  During the wet season ____ swell and during the dry season _____ shrinks.This mov’t aids dispersal of ascia….
  Apothecia -

Question 17

What are the 2 main fruiting bodies of the lichen

Question 18

Describe the fruitive body - Apothecia

Answer 18

• are saucer shaped
• sessile or stalked
• vary in shape
• mainly distributed at the margin but at times also found on lower surface of thallus
• spores are produced in structures called asci (s; ascus)
• spores must meet with a compatible alarm partner before a functional lichen can form (they are produced from fungal component)
• ## reproduction is mainly asexual/ vegetative means of soredia and isidia

Question 19

Distinguish btn the primary and secondary lichen products (metabolites)

Answer 19

Primary metabolites include carbohydrates, protein, lipids and other substances that make up the lichen structure
Are produced by both the myco- and phycobiont components
Secondary metabolites/ acids…
Produced by …. only.
Lichen acids are thought to function as general biocides; may deter slugs, bacteria and