best evidence that the relationship between alga and the fungus in the lichen is mutualistic
One of the best pieces of evidence that supports the mutualistic relationship between algae and fungi in a lichen is the inability of each partner to survive and function independently.
1. Algae, usually green or blue-green algae, provide essential photosynthetic capabilities to the lichen. They convert sunlight and carbon dioxide into organic compounds, such as sugars, which can be used as a source of energy for both the alga and fungus. Without the algae, the lichen would not be able to obtain sufficient energy to survive.
2. On the other hand, fungi provide a protective and supportive structure for the algae. They form a complex network of filaments called hyphae, which create a physical framework for the lichen. This structure offers protection against desiccation, harmful ultraviolet radiation, and extreme temperatures. Without the fungi, the algae would be exposed and vulnerable to these environmental stresses.
3. Another piece of evidence pointing to mutualism is the fact that the growth rate and reproductive success of lichens are often higher when both the alga and fungus are present together. In laboratory studies, when the algae and fungi are artificially separated, the growth of both partners is significantly reduced.
4. Lichens have been found in a wide range of extreme habitats, including deserts, mountains, and polar regions. Their ability to colonize these challenging environments is primarily due to the combined survival strategies of both the alga and fungus. The alga provides nutrients, while the fungus provides physical protection, allowing lichens to thrive in areas where neither partner could survive alone.
5. Genetic and molecular studies have also revealed close and specific interactions between algal and fungal partners. The alga and fungus within a lichen show coordinated gene expression, suggesting a mutualistic relationship in which both partners are dependent on each other for survival and function.
Overall, the interdependence, shared benefits, and inability to survive independently make a strong case for the mutualistic relationship between algae and fungi in lichens.