Both lichens and corals are symbioses involving phototrophic microorganisms

Question

Compare and contrast lichens and corals, including the types of organisms involved, the role of each partner, the specificity of the interaction, and the method of transmission for each symbiosis.
What will be an ideal response?

Answer 1

Answer: Lichens are found on house roofs, tree trunks, rocks, and soils. A lichen contains a fungus, which attaches to the surface and provides its mutualistic partner, either an alga or cyanobacterium, with increased access to inorganic nutrients. The fungus also prevents desiccation of the phototrophs by sequestering water and protects the phototroph from erosion in exposed environments. The phototroph produces organic carbon (sugars), which benefit the fungus. Some cyanobacteria also provide a fixed nitrogen source to the fungi. Many different fungi form associations with only a few different phototrophs, and the same phototroph can form an association with multiple fungi.
Corals are similar to lichens in that the cnidarian coral body provides protection for the phototroph (a dinoflagellate). The two partners also exchange the same nutrients â€" organic carbon in exchange for inorganic nutrients (N, P, and CO2). However, the coral provides an additional benefit to the phototroph by increasing the collection of solar radiation for photosynthesis. Coral symbioses are also different in that the association between the coral host and the dinoflagellate symbiont is much more specific. Transmission of the symbiont is vertical â€" the symbiont is present in the egg before it is released from the parent, although free-living forms of the symbiont do survive outside of the host. The partners have specific recognition signals and specialized structures to coordinate growth and nutritional exchange.