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: Understanding the Concept:
Nitrogen is an essential macronutrient for plants. While the atmosphere is rich in nitrogen gas (N\(_2\)), plants cannot use it directly. They must absorb nitrogen from the soil in specific inorganic forms. The question asks to identify these forms.
Step 2: Detailed Explanation:


Plants primarily absorb nitrogen from the soil through their root systems.

The two major inorganic forms of nitrogen that plant roots can take up and assimilate are nitrate (NO\(_3^-\)) and ammonium (NH\(_4^+\)).

Nitrate (D) is typically the most abundant form in well-aerated soils and is highly mobile. Once absorbed, it must be reduced to ammonium before it can be incorporated into amino acids.

Ammonium (B) can be taken up directly and is energetically cheaper to use since it does not need to be reduced. However, it is less mobile in soil and can be toxic at high concentrations.

Nitrite (A) is an intermediate in the nitrogen cycle (nitrification and denitrification) but is not a major form of nitrogen taken up by plants; it can also be toxic. Nitric acid (C) is not a form of nitrogen assimilated from the soil.

Step 3: Final Answer:
The two inorganic forms of nitrogen that plants can assimilate are ammonium (B) and nitrate (D).