Calcium:
(a) Is required by meristematic and differentiating tissues
(b) Is needed during formation of mitotic spindle

Options

A. Only (a) is correct
B. Both (a) and (b) are correct
C. Only (b) is correct
D. Both (a) & (b ) are incorrect

Answer

**Step-by-Step Solution:**

1. **Understanding Calcium's Role in Plants:**
- Calcium is classified as a macronutrient, which means it is required in relatively large amounts by plants. It is absorbed in the form of calcium ions (Ca²⁺).

2. **Calcium in Meristematic and Differentiating Tissues:**
- The first statement claims that calcium is required by meristematic and differentiating tissues. This is true because calcium plays a crucial role in cell division and the synthesis of the cell wall. Meristematic tissues are regions of active cell division, and calcium is essential for the proper functioning of these processes.

3. **Calcium in Mitotic Spindle Formation:**
- The second statement states that calcium is needed during the formation of the mitotic spindle. This is also correct. Calcium ions are involved in the regulation of various cellular processes, including the formation of the mitotic spindle, which is crucial for the separation of chromosomes during cell division. Calcium stimulates the onset of anaphase, a key phase in mitosis.

4. **Conclusion:**
- Both statements (a) and (b) are correct. Therefore, the correct answer is that both A and B are correct.

**Final Answer:**
Both statements regarding calcium are correct.