Question

Plants can assimilate only two inorganic forms of nitrogen. These are:
A. Nitrite (NO\(_2^-\))
B. Ammonium (NH\(_4^+\))
C. Nitric acid (HNO\(_3\))
D. Nitrate (NO\(_3^-\))
Choose the correct answer from the options given below:

• A. A and D only
• B. B and D only
• C. B, C and D only
• D. A, B and D only

Hint:

Remember that plants "eat" nitrogen in two main forms from the soil: nitrate (NO\(_3^-\)) and ammonium (NH\(_4^+\)). All other forms of nitrogen in the soil are generally converted to one of these two forms before the plant can use them.

Answer 1

The Correct Option is B

Step 1: Concept Overview:
Plants require nitrogen as a key macronutrient but cannot directly use atmospheric nitrogen gas (N\(_2\)). They must obtain it from the soil in specific inorganic forms. This question asks us to identify those forms.
Step 2: Detailed Explanation:


Plants absorb nitrogen from the soil via their roots.

The two primary inorganic nitrogen forms absorbed and utilized by plants are nitrate (NO\(_3^-\)) and ammonium (NH\(_4^+\)).

Nitrate (D) is typically abundant in well-aerated soils and is highly mobile. It requires reduction to ammonium before incorporation into amino acids.

Ammonium (B) can be directly absorbed. It's energetically favorable but less mobile and potentially toxic at high concentrations.

Nitrite (A) is an intermediate in the nitrogen cycle, not a major uptake form, and can be toxic. Nitric acid (C) is not assimilated from the soil.

Step 3: Conclusion:
The inorganic nitrogen forms plants assimilate are ammonium (B) and nitrate (D).