Question

The possible resource of phosphorus ions and nitrogen ions in soil generally get depleted, because they are usually found as
A. Positively charged ions
B. Negatively charged ions
C. A disproportionate mixture of negatively charged ion
D. Particle carrying no charge

Answer 1

Hint: Nitrogen and phosphorus are important molecules for the plants. Nitrogen and phosphorus are the important constituents of genetic material DNA, RNA. Phosphorus is important for synthesis of energy molecule ATP.

Complete Answer:
- Soil is a mixture of sand, organic matter, silt, clay. The soil with more sand content has low binding capacity for cations or positively charged ions. The clay and silt are negatively charged so then can easily adsorb and hold cations. This is the reason the cations like calcium, sodium are not easily depleted.
- The nitrogen and phosphorus cannot be absorbed in the molecular form by the plants. They are converted into phosphates, biphosphates or nitrates, nitrites by the bacteria present in the soil. The nitrogen and phosphorus are thus negatively charged. They are loosely held by the clay. This is the reason they are prone to depletion.

Thus the correct answer is (B).

Note: Plants absorb minerals by the active transport against the concentration gradient at the cost of ATP. The anions are more prone to leaching by surface water and water logging. So the plants cannot absorb more of the anions from the soil. The nitrogen and phosphorus are substituted in the oil by the help of fertilizers like urea, super phosphate.