Question

practical activity: lichens
find out: what is a lichen? what organisms are working together to create lichen?
what kind of symbiosis does the make-up of lichen represent?
do lichens have roots? why not? (hint: find out if either algae or fungus has roots)
what does the algae provide for lichen?
what does the fungus provide for lichen?
observe the lichen on both the wood and the rock under the stereoscope. what do you notice different between the lichens growing on the two substrates?

Explanation:

To answer these questions about lichens, we analyze each one:

1. What is a lichen? What organisms create it?

A lichen is a composite organism resulting from a mutualistic symbiosis between a fungus (usually an ascomycete or basidiomycete) and a photosynthetic partner (either a green alga or a cyanobacterium). The fungus and the photosynthetic organism (alga/cyanobacterium) work together to form the lichen.

2. What kind of symbiosis? What do they represent?

Lichens exhibit mutualism (both partners benefit). The fungus provides a protective structure (thallus) and absorbs water/minerals. The alga/cyanobacterium (photobiont) provides organic carbon (via photosynthesis) and oxygen. The “make - up” of a lichen represents a stable, long - term symbiotic relationship where the fungus (mycobiont) and photobiont are interdependent.

3. Do lichens have roots? Why not?

Lichens do not have true roots. True roots (like in plants) are for water/nutrient absorption and anchoring, and are made of vascular plant tissue. Lichens have rhizines (hair - like structures) for anchoring, but they lack the specialized root - like structures of plants. The fungus absorbs water and minerals directly from the air, rain, or substrate surface, so true roots are unnecessary.

4. What does the algae provide?

The algal (or cyanobacterial) partner in a lichen provides organic compounds (like glucose) through photosynthesis. These compounds are the primary energy source for the lichen. Cyanobacteria also fix atmospheric nitrogen, providing a nitrogen source for the lichen.

5. What does the fungus provide?

The fungal partner provides a protective thallus structure that shields the photobiont from harsh environmental conditions (e.g., UV radiation, desiccation). The fungus also absorbs water and minerals from the surrounding environment (air, rain, substrate) and transports these resources to the photobiont.

6. Observe lichens on wood and rock. What’s different?

• Substrate Interaction: On wood (a carbon - rich, organic substrate), lichens may decompose lignin/cellulose over time (some are “lignicolous”). On rock (inorganic, mineral - rich), lichens contribute to biological weathering (secreting acids to break down rock, aiding soil formation).
• Morphology: Lichens on rock (e.g., crustose lichens) often have a crust - like, tightly attached form to withstand wind/erosion. On wood, they may be more leaf - like (foliose) or branching (fruticose) if the wood is stable and moist.
• Microenvironment: Wood retains more moisture and organic matter, so lichens on wood may have a more diverse community or faster growth (depending on the wood’s decay stage) compared to the often harsher, drier rock surface.

These answers draw from concepts in Biology (specifically mycology, algology, and symbiosis) and Ecology (substrate - organism interactions).

Answer:

To answer these questions about lichens, we analyze each one:

1. What is a lichen? What organisms create it?

A lichen is a composite organism resulting from a mutualistic symbiosis between a fungus (usually an ascomycete or basidiomycete) and a photosynthetic partner (either a green alga or a cyanobacterium). The fungus and the photosynthetic organism (alga/cyanobacterium) work together to form the lichen.

2. What kind of symbiosis? What do they represent?

Lichens exhibit mutualism (both partners benefit). The fungus provides a protective structure (thallus) and absorbs water/minerals. The alga/cyanobacterium (photobiont) provides organic carbon (via photosynthesis) and oxygen. The “make - up” of a lichen represents a stable, long - term symbiotic relationship where the fungus (mycobiont) and photobiont are interdependent.

3. Do lichens have roots? Why not?

Lichens do not have true roots. True roots (like in plants) are for water/nutrient absorption and anchoring, and are made of vascular plant tissue. Lichens have rhizines (hair - like structures) for anchoring, but they lack the specialized root - like structures of plants. The fungus absorbs water and minerals directly from the air, rain, or substrate surface, so true roots are unnecessary.

4. What does the algae provide?

The algal (or cyanobacterial) partner in a lichen provides organic compounds (like glucose) through photosynthesis. These compounds are the primary energy source for the lichen. Cyanobacteria also fix atmospheric nitrogen, providing a nitrogen source for the lichen.

5. What does the fungus provide?

The fungal partner provides a protective thallus structure that shields the photobiont from harsh environmental conditions (e.g., UV radiation, desiccation). The fungus also absorbs water and minerals from the surrounding environment (air, rain, substrate) and transports these resources to the photobiont.

6. Observe lichens on wood and rock. What’s different?

• Substrate Interaction: On wood (a carbon - rich, organic substrate), lichens may decompose lignin/cellulose over time (some are “lignicolous”). On rock (inorganic, mineral - rich), lichens contribute to biological weathering (secreting acids to break down rock, aiding soil formation).
• Morphology: Lichens on rock (e.g., crustose lichens) often have a crust - like, tightly attached form to withstand wind/erosion. On wood, they may be more leaf - like (foliose) or branching (fruticose) if the wood is stable and moist.
• Microenvironment: Wood retains more moisture and organic matter, so lichens on wood may have a more diverse community or faster growth (depending on the wood’s decay stage) compared to the often harsher, drier rock surface.

These answers draw from concepts in Biology (specifically mycology, algology, and symbiosis) and Ecology (substrate - organism interactions).