In reference to biological role, `Ca^(2+)` ions are important in

Options

A. triggering the contraction of muscles
B. generating the right electrode potential across cell membrane
C. hydrolysis of ATP
D. defence mechanism

Explanation

To determine the biological role of \( \text{Ca}^{2+} \) ions, we will analyze each of the provided options step by step.

### Step 1: Analyze Option A - Triggering the Contraction of Muscles
Calcium ions (\( \text{Ca}^{2+} \)) are known to play a crucial role in muscle contraction. When a muscle cell is stimulated, \( \text{Ca}^{2+} \) ions are released from the sarcoplasmic reticulum into the cytoplasm. This increase in calcium concentration allows the interaction between actin and myosin, the proteins responsible for muscle contraction. Therefore, this option is likely correct.

**Hint:** Think about how muscles contract and the role of calcium in that process.

### Step 2: Analyze Option B - Generating the Right Electrode Potential Across Cell Membrane
The generation of the resting membrane potential and action potentials in neurons and muscle cells is primarily due to the movement of sodium (\( \text{Na}^{+} \)) and potassium (\( \text{K}^{+} \)) ions across the cell membrane. While calcium ions do play a role in signaling, they are not the primary ions responsible for establishing the resting membrane potential. Thus, this option can be eliminated.

**Hint:** Consider which ions are primarily involved in generating electrical potentials in cells.

### Step 3: Analyze Option C - Hydrolysis of ATP
ATP hydrolysis is a chemical reaction that releases energy, and it is primarily catalyzed by enzymes such as ATPases. Calcium ions do not directly participate in the hydrolysis of ATP; rather, they may influence certain ATP-dependent processes but are not essential for the hydrolysis itself. Therefore, this option can also be eliminated.

**Hint:** Recall the role of ATP and the enzymes involved in its hydrolysis.

### Step 4: Analyze Option D - Defense Mechanism
Calcium ions are not directly involved in the immune response or the activation of antibodies. The defense mechanisms in the body are primarily mediated by various types of cells and proteins, such as antibodies and white blood cells. Thus, this option is not relevant to the role of \( \text{Ca}^{2+} \).

**Hint:** Think about how the immune system functions and what components are involved.

### Conclusion
After analyzing all the options, we find that the only correct answer regarding the biological role of \( \text{Ca}^{2+} \) ions is:

**Correct Answer: A - Triggering the contraction of muscles.**