How many of the following statements describing the functions of Mn are true?
I .Mn is required during non - cyclic photophosphorylation
II. Mn competes with iron and magnesium for uptake .
III.Mn promotes calcium translocation in the shoot apex.
IV. Mn is an activator of many respiratory enzymes.

Options

A. 3
B. 4
C. 2
D. 1

Answer

To determine how many of the statements regarding the functions of manganese (Mn) are true, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: Mn is required during non-cyclic photophosphorylation.**
- **Analysis:** Manganese plays a crucial role in photosynthesis, particularly in the water-splitting reaction during non-cyclic photophosphorylation. It is essential for the functioning of photosystem II.
- **Conclusion:** This statement is **True**.

2. **Statement II: Mn competes with iron and magnesium for uptake.**
- **Analysis:** Manganese does compete with iron and magnesium for uptake in plants. When there is excess manganese, it can inhibit the absorption of these essential nutrients.
- **Conclusion:** This statement is **True**.

3. **Statement III: Mn promotes calcium translocation in the shoot apex.**
- **Analysis:** This statement is incorrect. Manganese does not promote calcium translocation; rather, it inhibits it. Excess manganese can hinder the movement of calcium to the shoot apex.
- **Conclusion:** This statement is **False**.

4. **Statement IV: Mn is an activator of many respiratory enzymes.**
- **Analysis:** Manganese is indeed an important cofactor for various enzymes involved in respiration, thus playing a significant role in the respiratory processes of plants.
- **Conclusion:** This statement is **True**.

### Final Count of True Statements:
- True Statements: I, II, IV
- False Statement: III

Therefore, the total number of true statements is **3**.