(a) Protein carrier molecules : Carrier proteins facilitate the diffusion of different molecules, to which they have specificity, one molecule at the time is allowed to bind to carrier protein and is released on the other side of the membrane. These are present in plasmalemma. These molecules take energy from ATP molecules and then pick up mineral molecules from the soil and carry them inward and release into cytoplasm.
Hidden hunger refers to a situation in which a crop needs more of a given nutrient yet has shown no deficiency symptoms. The nutrient content is above the deficiency symptom zone but still considerably needed for optimum crop production
The nitrogenase enzyme is very sensitive to the molecular oxygen. It requires anaerobic conditions to work. The leg-haemoglobin in the nodule acts as an oxygen scavenger just meainting the anaerobic condition needed by the enzyme.