Which organism forms the fungal partner in a mycorrhizal association with tree roots?

• A. Nematodes
• B. Algae
• C. Bacteria
• D. Mycorrhizal fungus

Answer: (D)

In a mycorrhizal association, the fungal partner is a fungus that forms a symbiotic link with tree roots. The mycorrhizal fungus extends hyphae into the soil, greatly increasing the root’s surface area to absorb water and nutrients (especially phosphorus). In return, the tree supplies the fungus with carbohydrates produced by photosynthesis. Nematodes, algae, and bacteria are different kinds of organisms and do not serve as the fungal partner in this relationship. Therefore, the organism forming the fungal partner is the mycorrhizal fungus.