Question

Which of the following element is the latest inclusion as the essential nutrient element

• A. Boron
• B. Cobalt
• C. Chlorine
• D. Nickel

Hint:

Remember the number 17.
Nickel was the "last one in" (1987).
It is needed for "Urea" metabolism. Without Ni, urea accumulates to toxic levels in leaves!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the 17th and most recently officially recognized essential plant nutrient among the choices provided.
Detailed Explanation:

• Criteria for Essentiality:
Arnon and Stout (1939) established the criteria: The plant cannot complete its life cycle without it, its function is specific and cannot be replaced, and it is directly involved in metabolism.

• The Timeline of Discovery:
Most micronutrients (Fe, Mn, Zn, Cu, B, Mo) were identified in the early 20th century.
Chlorine (Cl) was established as essential in 1954.
Nickel (Ni) was the latest addition, officially recognized as essential for all higher plants in 1987 (by Brown et al.). It is a critical component of the enzyme urease, which breaks down urea.

• Analyzing other options:
Boron: Identified in 1923 by Warington.
Cobalt: Essential for nitrogen-fixing bacteria in legumes (beneficial) but not universally essential for all plants.

• Current Count:
There are now 17 universally essential elements: C, H, O (from air/water) and N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl, Ni (from soil).

Step 2: Final Answer:
Nickel is the latest addition to the list of essential plant nutrients.