Transport in Plants & Mineral Nutrition — Essential NEET Facts — Summary

Water potential equation: Ψw = Ψs + Ψp. Ψs is always negative; Ψp is positive in turgid cells. Pure water Ψw = 0. Water moves from higher to lower Ψw.
Plasmolysis occurs when cells are placed in hypertonic solution; protoplast shrinks from cell wall. Incipient plasmolysis: Ψp = 0.
Imbibition = adsorption of water by hydrophilic colloids (cellulose, starch, proteins); no semipermeable membrane needed; generates high imbibition pressure.
Apoplast pathway: through cell walls and intercellular spaces; fast; non-selective.
Symplast pathway: through cytoplasm via plasmodesmata; slow; selective.
Casparian strip: suberin band in endodermal cell walls; blocks apoplast at endodermis; forces all water and minerals into symplast.
Root pressure: positive hydrostatic pressure in root xylem; causes guttation (liquid water through hydathodes at night/early morning).
Cohesion-tension theory (Dixon and Joly): main mechanism of water ascent; transpiration pull creates tension; cohesion (H-bonds) + adhesion maintains continuous xylem water column.
Transpiration: 90–95% stomatal, 5–10% cuticular, <1% lenticular.
Guard cells open stomata via $K^{+}$ influx (light-driven); ABA signals stomatal closure during water stress.
17 essential elements: 9 macronutrients (C, H, O, N, P, K, Ca, Mg, S) + 8 micronutrients (Fe, Mn, Zn, Cu, Mo, B, Cl, Ni).
Arnon & Stout criteria: absolutely necessary, non-substitutable, directly involved in metabolism.
Mobile elements (N, P, K, Mg): deficiency shows first in older leaves.
Immobile elements (Ca, Fe, S, Mn, B): deficiency shows first in younger leaves.
Nitrogenase: Mo-Fe protein; requires 16 ATP; strictly anaerobic; reaction: $N_{2}$ + 8 $H^{+}$ + 8 $e^{-}$ + 16 ATP → $2NH_{3}$ + $H_{2}$ + 16 ADP + 16 Pᵢ.
Leghemoglobin: red pigment in legume nodules; scavenges $O_{2}$ to protect nitrogenase.
Rhizobium: symbiotic nitrogen fixer in legume root nodules.
Azotobacter: free-living aerobic nitrogen fixer.
Clostridium: free-living anaerobic nitrogen fixer.
Heterocysts: thick-walled anaerobic cells in Anabaena and Nostoc where $N_{2}$ fixation occurs.
Nitrification: Nitrosomonas ( $NH_{3}$ → $NO_{2}^{-}$ ) → Nitrobacter ( $NO_{2}^{-}$ → $NO_{3}^{-}$ ); both are chemoautotrophs.
Denitrification: Pseudomonas and Thiobacillus ( $NO_{3}^{-}$ → $N_{2}$ ).