The requriement of essential element must be (A)____ and not replaceable by another (B)_____

Answer

To answer the question regarding the requirement of essential elements in plants, we can break it down into two parts:

1. **Requirement of Essential Element Must Be (A)**: The essential elements required by plants must be specific. This means that each essential element has a unique role in the plant's physiological processes. For example, nitrogen is crucial for protein synthesis, while phosphorus is important for energy transfer and nucleic acid formation. Therefore, the requirement of essential elements must be **specific**.

2. **Not Replaceable by Another (B)**: Essential elements cannot be substituted by other elements. This means that if a plant requires a specific element for a particular function, no other element can fulfill that role. For instance, if a plant needs magnesium for chlorophyll production, it cannot replace magnesium with calcium or any other element. Hence, the essential elements must be **non-substitutable**.

Putting it all together, the complete answer to the question is: The requirement of essential element must be **specific** and not replaceable by another **non-substitutable**.