Lichens are found growing on trees, walls, rocks and soil.
Fig. 9.1 shows a lichen of the genus Usnea. Usnea can tolerate only low concentrations of sulfur dioxide and does not grow in places where the air is polluted with sulfur dioxide
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Usnea is composed of a mixture of two types of cell:
- photosynthetic cells that are classified in the kingdom Protoctista
- fungal cells that are classified in the kingdom Fungi.
(a) Outline the characteristic features of the kingdoms Protoctista and Fungi.
(b) Xanthoria is a lichen that can grow in places where there is a high concentration of sulfur dioxide in the air, for example in towns where homes, factories and vehicles burn fuels.
(i) A student planned a method to measure the relative abundance of Usnea and Xanthoria on trees along a transect from the town centre at 0 km to unpolluted countryside at 4 km.
Suggest why measuring the relative abundance of the two types of lichen gives information that is useful for conservation.
(ii) Although a large biodiversity of lichens can be found in a range of habitats, most people ignore them.
Outline why forms of life that are usually ignored, such as lichens, should be conserved.
▶️ Answer/Explanation
(a) Characteristic features of Protoctista and Fungi:
Protoctista:
- Eukaryotic organisms that don’t fit into other kingdoms
- Most are unicellular but some are multicellular (like algae)
- Can be autotrophic (like algae) or heterotrophic (like protozoa)
- Cell walls when present may contain cellulose
- Reproduce both sexually and asexually
Fungi:
- Eukaryotic, mostly multicellular organisms
- Cell walls made of chitin
- Heterotrophic (saprotrophic or parasitic)
- Body composed of hyphae that form mycelium
- Reproduce via spores (both sexually and asexually)
- Store food as glycogen
Explanation: The Protoctista kingdom is essentially a “catch-all” group for eukaryotic organisms that don’t fit into the other kingdoms. They show great diversity in form and function. Fungi, while also eukaryotic, have distinct characteristics like chitinous cell walls and a filamentous structure that set them apart.
(b)(i) Why measuring lichen abundance is useful for conservation:
- Lichens are excellent bioindicators of air quality, particularly sulfur dioxide pollution
- The relative abundance of pollution-sensitive (Usnea) versus pollution-tolerant (Xanthoria) species provides a visual map of pollution levels across the transect
- This information helps identify areas needing pollution control measures
- Changes in lichen populations can indicate improvements or worsening of air quality over time
- Protecting lichen diversity helps maintain ecosystems where they serve as food and habitat for other organisms
Explanation: Lichens are nature’s pollution monitors. Their sensitivity to air quality changes makes them valuable tools for environmental assessment. By tracking their distribution, we can identify pollution hotspots and monitor the effectiveness of conservation efforts without expensive equipment.
(b)(ii) Why often-ignored organisms like lichens should be conserved:
- Lichens play crucial roles in ecosystems as pioneer species, helping to form soil and create habitats
- They are important food sources for many animals, particularly in harsh environments
- They contribute to biodiversity which maintains ecosystem resilience
- Lichens have potential medicinal uses (many produce unique antibiotic compounds)
- They contribute to nutrient cycling by fixing nitrogen and breaking down rocks
- Ethically, all species have intrinsic value regardless of their visibility or usefulness to humans
- They may hold undiscovered benefits that could be important for future generations
Explanation: While lichens might not be as charismatic as pandas or tigers, they perform essential ecosystem services. Their conservation is important because they represent unique evolutionary adaptations and contribute to the overall health of ecosystems. The fact that they’re often overlooked makes them particularly vulnerable to habitat destruction and pollution, so conscious conservation efforts are needed.