Transport in Plants & Mineral Nutrition — Mistakes to Avoid — Summary

Confusing guttation with transpiration: Guttation is liquid water loss through hydathodes driven by root pressure at night. Transpiration is water vapour loss through stomata driven by cohesion-tension during the day. They are mutually exclusive mechanisms.
Reversing Nitrosomonas and Nitrobacter: Nitrosomonas converts $NH_{3}$ → $NO_{2}^{-}$ (step 1). Nitrobacter converts $NO_{2}^{-}$ → $NO_{3}^{-}$ (step 2). Exam setters routinely swap the two — fix the order with "Nitroso first, Nitro second."
Thinking apoplast crosses membranes: The apoplast pathway is entirely extracellular — it never crosses a plasma membrane. Only the symplast pathway involves membrane crossings.
Placing Casparian strip in the wrong layer: It is in the endodermis, not the cortex or pericycle. It is on the radial and transverse walls, not the tangential walls.
Mobile vs immobile nutrient location: Mobile deficiency (N, P, K, Mg) appears in older leaves first. Immobile deficiency (Ca, Fe, Mn, B) appears in younger leaves first. Mixing these up is the single most common error in this chapter.
Nitrogenase and oxygen: Nitrogenase is irreversibly inhibited by $O_{2}$ — it is not merely slowed down, it is permanently destroyed. Leghemoglobin's role is therefore protective, not catalytic.
Misidentifying leghemoglobin's function: Leghemoglobin scavenges free oxygen; it does not fix nitrogen. Students sometimes attribute nitrogen fixation to leghemoglobin itself.
Counting essential elements: There are 17 essential elements — 9 macro + 8 micro. Nitrogen (N) is a macronutrient; Iron (Fe) is a micronutrient despite its historical inclusion in the "C. Hopkins CaFe Mg" mnemonic.
Root pressure vs transpiration pull in tall trees: Root pressure is insufficient to raise water to the top of tall trees. The cohesion-tension (transpiration pull) mechanism is the primary driver of water ascent.
Imbibition vs osmosis: Imbibition does not require a semipermeable membrane and involves adsorption by colloids. Osmosis requires a semipermeable membrane and involves concentration gradients.