Transport in Plants & Mineral Nutrition — 5 Must-Know Facts — Summary

Casparian strip (suberin, endodermis) blocks the apoplast pathway, forcing all water and minerals into the selective symplast — the root's mineral gatekeeper.
Guttation = liquid water through hydathodes at night due to root pressure. Transpiration = water vapour through stomata during the day due to cohesion-tension. Never confuse these two.
Nitrogenase is a Mo-Fe protein requiring 16 ATP and strictly anaerobic conditions; leghemoglobin scavenges $O_{2}$ to protect it in legume nodules.
Nitrosomonas converts $NH_{3}$ → $NO_{2}^{-}$ (step 1); Nitrobacter converts $NO_{2}^{-}$ → $NO_{3}^{-}$ (step 2). Pseudomonas denitrifies $NO_{3}^{-}$ → $N_{2}$ .
Mobile deficiency (N, P, K, Mg) → older leaves affected first. Immobile deficiency (Ca, Fe, Mn, B) → younger leaves affected first.