USA Biology Olympiad (USABO) Practice Exam

What is the primary function of arbuscules in endomycorrhizae?

1. Serve as a nutrient/water bridge between fungus and plant root.

2. Facilitate gas exchange between soil and plant.

3. Store excess carbohydrates during photosynthesis.

4. Conduct defense responses against pathogens.

The correct answer is: Serve as a nutrient/water bridge between fungus and plant root.

The primary function of arbuscules in endomycorrhizae is to serve as a nutrient/water bridge between the fungus and the plant root. Arbuscules are specialized structures formed by the fungal partner during the symbiotic interaction with plant roots. They increase the surface area for exchange, allowing for more efficient transfer of essential nutrients, such as phosphorus, and water from the fungus to the plant. In turn, the plant provides carbohydrates to the fungus, which are produced during photosynthesis. This mutualistic relationship enhances nutrient uptake for the plant, especially in nutrient-poor soils, highlighting the importance of arbuscules in facilitating this critical exchange in mycorrhizal associations.