Answer: Ectomycorrhizae form a sheath around roots and penetrate between cortical cells (Hartig net) but not into cells; arbuscular mycorrhizae penetrate into cortical cells forming arbuscules (tree-like structures).
- A Both fungal types are sometimes reported to penetrate root cortical cells in a largely identical structural manner, with little meaningful difference between them in most textbook accounts during normal conditions
- B Ectomycorrhizae form a sheath around roots and penetrate between cortical cells (Hartig net) but not into cells; arbuscular mycorrhizae penetrate into cortical cells forming arbuscules (tree-like structures)
- C Ectomycorrhizae are described as being associated mainly with agricultural crop plants in general; arbuscular mycorrhizae mainly with large forest trees instead as generally observed in typical laboratory settings
- D Arbuscular mycorrhizae are sometimes said to form a largely parasitic, mostly non-mutualistic relationship with their host plant in many documented cases under usual circumstances according to most researchers
Correct answer: B. Ectomycorrhizae form a sheath around roots and penetrate between cortical cells (Hartig net) but not into cells; arbuscular mycorrhizae penetrate into cortical cells forming arbuscules (tree-like structures)
Explanation: Ectomycorrhizae: hyphae form a mantle around roots and grow between cortical cells (Hartig net); found in many trees (oak, pine). Arbuscular (endomycorrhizae/AM fungi): penetrate into cortical cells forming arbuscules for nutrient exchange and vesicles for storage; most common type, found in ~80% of plant species.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.