Practice question

Arbuscules denote finely branched intracellular haustorial structures formed by glomeromycotan mycorrhizal fungi within root cortical cells of vascular plants including most crops. Arbuscule branches massively increase interfacial surface area for bidirectional nutrient exchange: fungus delivers phosphate and micronutrients absorbed from soil via extraradical hyphae to plant, plant supplies photosynthate carbohydrates and lipids to obligate fungal symbiont. Formed during arbuscular mycorrhizal symbiosis oldest and most widespread mutualism dating ~400 million years. Not associated with parasitic, saprophytic or predatory strategies but mutualistic mycorrhizal interface.