Lichens

Question 1

What is lichenology?

Answer 1

Lichenology is the study of lichens.

Question 2

Define a lichen thallus and its components.

Answer 2

A lichen thallus is the plant body of lichens, which consists of a symbiotic relationship between fungi (mycobiont) and algae (phycobiont).

Question 3

What is the difference between a mycobiont and a phycobiont?

Answer 3

The mycobiont is the fungal component, usually an ascomycete, while the phycobiont is the algal component, which may be green algae or cyanobacteria.

Question 4

Name the three layers of the lichen thallus.

Answer 4

The three layers are the cortex, algal layer, and medulla.

Question 5

Describe the structure and function of the cortex in lichens.

Answer 5

The cortex is the protective outer layer composed of tightly packed fungal hyphae. It reduces UV radiation and prevents microbial invasion.

Question 6

What are the roles of haustoria in lichens?

Answer 6

Haustoria are specialized fungal hyphae that penetrate algal cells, aiding in nutrient absorption.

Question 7

Explain the medulla layer in lichens and its significance.

Answer 7

The medulla consists of loosely packed fungal hyphae and functions as a water reservoir and stores lichen acids.

Question 8

List two types of algae commonly found as phycobionts in lichens.

Answer 8

Green algae (e.g., Trebouxia) and cyanobacteria (e.g., Nostoc).

Question 9

Name the four growth forms of lichens with examples.

Answer 9

Crustose (e.g., Graphis), foliose (e.g., Parmelia), fruticose (e.g., Usnea), and squamulose (e.g., Placidium).

Question 10

How do crustose lichens differ from foliose lichens?

Answer 10

Crustose lichens are closely attached to substrates,have 3 distinct layers whereas foliose lichens have leaf-like structures and have rhizines that emerge from lower cortex with 4 layers; cortex, algal, medulla, lower cortex.

Question 11

What are squamulose lichens?

Answer 11

Squamulose lichens consist of tightly packed and slightly flattened pebble-like structures.

Question 12

Describe fruticose lichens and provide two examples.

Answer 12

Fruticose lichens are shrubby or hair-like and include species like Cladonia and Usnea.

Question 13

What are soredia, and how do they help in vegetative propagation?

Answer 13

Soredia are clumps of algal cells enveloped by fungal hyphae, aiding in asexual reproduction.

Question 14

Define isidia and their role in lichen reproduction.

Answer 14

Isidia are finger-like outgrowths on the upper cortex containing both fungal and algal components, are fragile and when broken off the pieces act as vegetative propagules. Found in folios and fructose

Question 15

Differentiate between cyphellae and pseudocyphellae.

Answer 15

Cyphellae are large pits for gas exchange found on the lower cortex, while pseudocyphellae are smaller and occur on both surfaces.

Question 16

What are the main fruiting bodies in lichens, and how do they differ?

Answer 16

The main fruiting bodies are perithecia (flask-shaped) and apothecia (cup-like).

Question 17

Describe the role of apothecia in lichen reproduction.

Answer 17

Apothecia produce spores in asci, which must meet compatible algae to form new lichens.

Question 18

What are lichen acids, and how are they formed?

Answer 18

Lichen acids are secondary metabolites secreted by fungal hyphae, providing UV protection and deterring herbivores.

Question 19

Explain the economic relevance of lichens in the textile industry.

Answer 19

Lichens produce dyes (e.g., Parmelia saxatilis) used in fabrics.

Question 20

How are lichens used as indicators of air pollution?

Answer 20

Lichens are sensitive to air pollution esp. sulfur dioxide and indicate air quality.

Question 21

Describe the importance of lichens in nitrogen fixation.

Answer 21

Lichens containing cyanobacteria (e.g., Nostoc) fix atmospheric nitrogen.

Question 22

What is the significance of the lichen species Trebouxia?

Answer 22

Trebouxia is a common unicellular green alga found as a phycobiont in lichens.

Question 23

How does the medulla contribute to water retention in lichens?

Answer 23

The medulla’s loosely packed hyphae store water for the lichen.

Question 24

Describe the relationship between lichens and UV protection.

Answer 24

Pigments and lichen acids in the cortex protect lichens from UV damage.

Question 25

How are lichens utilized in traditional medicine?

Answer 25

Lichen extracts, such as usnic acid, are used to treat wounds and sore throats.

Question 26

What pigments are found in lichens, and how are they used in systematics?

Answer 26

Pigments like parietin and usnic acid are used to classify lichens.

Question 27

Explain how lichens contribute to rock degradation.

Answer 27

Lichen acids chemically weather rocks, aiding in soil formation.

Question 28

What is the role of lichens in supporting animal diets?

Answer 28

Lichens, especially fruticose types, provide food for animals like reindeer.

Question 29

Discuss the structural adaptations that allow lichens to survive extreme conditions.

Answer 29

Lichens have a water-retentive medulla and UV-protective cortex.

Question 30

Compare haploid and diploid structures in the life cycle of lichens.

Answer 30

The fungal component is haploid, while the spore formation involves transient diploid stages.

Question 31

Give 5 general characteristics of lichens

Answer 31

• They grow in humid areas but can also withstand harsh conditions.
• The plant body is called thallus (not differentiated)
• Lichen thallus consists of 2 components; fungi and algae living in a symbiotic r/ship
• The mycobiont in most cases is an ascomycete, while the phycobiont consists of free-living algae eg chlorophyta and cyanophyta
• Lichen thallus has 3 main layers ; cortex, algal layer, medulla.

Question 32

Give 3 characteristics of the cortex

Answer 32

• it is a protective layer in contact with the environment.
• mainly composed of fungal hyphae
• serves to keep away other organisms and help reduce intense UV radiation which may damage algal cells
• may contain orange and yellow pigments, anthraquinones, pulvic derivatives, usnic acid.

Question 33

Give xtics of symbiotic layer

Answer 33

• also called algal layer
• composed of algal partner cells.
• are in close contact with fungal hyphae through haustoria
• haustoria - specialised food absorbing hyphae that penetrate algal cells and membanes

Question 34

What are the 5 different vegetative structures in lichens?

Answer 34

• soredia
• isidia
• cyphellae
• pseudocyphellae
• cephalodia

Question 35

What are cephalodia?

Answer 35

• outgrowths of the thallus containing foreign alga different from the host phycobiont.
• common in fruticose

Question 36

Describe and draw the structures of apothecia and perithecia

Answer 36

Perithecia
- consists of a fertile and sterile layer
- fertile; is called hymenium and contains asci(spore) bearing structures.
- mature spores are released through pore at top of perithecium called ostiole
- sterile layer; hamathecium consists of structures called papraphyses that aid is dispersal of spores.

Question 37

Differentiate between primary and secondary metabolites in lichen

Answer 37

primary ;
- produced by phycobiont and mycobiont
- carbohydrates, proteins, lipids and other structures that make up lichen
secondary;
- produced by mycobiont only
- are also called lichen acids
- function as general biocides; deter slugs, bacteria and other fungi.
- protect plant from harmful radiation thru sunlight
- e.g parietin and usnic acid

Question 38

what is the economic relevance of lichens?