Question

Which of the following statements are true about nitrogen nutrition in plant ?
(A) Nitrogen deficiency symptoms first appears on old leaf.
(B) Excess nitrogen causes early maturity of crop.
(C) Nitrogen translocated from old leaves to new leaves in response to demand.
(D) Nearly 10% of Indian soils are deficient in nitrogen.
(E) Nitrogen is constituent of chlorophyll, amino acids and nucleic acids.
Choose the correct answer from the options given below :

• A. (A), (B) and (E) only.
• B. (A), (B) and (D) only.
• C. (A), (C) and (E) only.
• D. (B), (C) and (D) only.

Hint:

To remember the effects of nitrogen:
- Deficiency \(\rightarrow\) Causes restricted growth and early senescent yellowing of older leaves.
- Excess \(\rightarrow\) Promotes lodging (succulent weak stems) and delays crop maturity.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Nitrogen is a primary macronutrient required by plants in the largest quantity.
It plays a fundamental role in plant biochemistry, serving as a structural block for essential macromolecules and metabolic processes.

Step 2: Detailed Explanation:
Let us evaluate each of the given statements regarding nitrogen nutrition:
- Statement (A): Nitrogen is highly mobile within the plant.
When a deficiency occurs, nitrogen is easily mobilized from older, mature leaves and transported to younger, active growing regions.
Consequently, chlorosis first appears on the older leaves, making this statement true.
- Statement (B): Excess nitrogen application stimulates rapid, vigorous vegetative growth, leading to thin cell walls and succulent tissues.
This delays the transition to reproductive growth and delays crop maturity, making this statement false.
- Statement (C): Because nitrogen is highly mobile, it is actively translocated from older senescing leaves to younger, developing leaves to meet their metabolic demands under nitrogen-limiting conditions, making this statement true.
- Statement (D): Almost all Indian soils are severely deficient in organic matter and nitrogen.
The deficiency level is widespread, typically exceeding 90% of cultivated soils, making the claim that "nearly 10% are deficient" false.
- Statement (E): Nitrogen is a key structural component of amino acids (the building blocks of proteins), nucleic acids (DNA and RNA), and the porphyrin ring of the green photosynthetic pigment chlorophyll, making this statement true.
Therefore, statements (A), (C), and (E) are the correct statements regarding nitrogen nutrition in plants.

Step 3: Final Answer:
The true statements are (A), (C), and (E) only, corresponding to Option C.