Read the following statements regarding muscle contraction
(i) One ATP utillised for making and breaking of the cross bridge.
(ii) The sarcomere lies between 2 Z-lines
(iii) Troponin blocks the active sites in resting stage
(iv) `Ca^(++)` ions help in unmasking active sites on HMM
Choose the correct option

Options

A. Only (i) is false
B. Only (ii) and (iii) are ture
C. Only (iv) is false
D. Only (ii) is false

Answer

To solve the question regarding muscle contraction, we will analyze each statement one by one to determine which ones are correct.

### Step-by-Step Solution:

1. **Statement (i): One ATP utilized for making and breaking of the cross bridge.**
- **Analysis:** This statement is incorrect. ATP is not used directly for making and breaking the cross-bridge; rather, it is hydrolyzed (split) to provide energy for the conformational changes in the myosin head that allow it to attach to and detach from actin.
- **Conclusion:** This statement is **false**.

2. **Statement (ii): The sarcomere lies between 2 Z-lines.**
- **Analysis:** This statement is correct. A sarcomere is defined as the segment of a myofibril that lies between two Z-lines (or Z-discs). It is the basic structural and functional unit of muscle contraction.
- **Conclusion:** This statement is **true**.

3. **Statement (iii): Troponin blocks the active sites in resting stage.**
- **Analysis:** This statement is also correct. In the resting state of muscle fibers, troponin binds to tropomyosin, which in turn blocks the active sites on actin filaments, preventing myosin from binding to actin.
- **Conclusion:** This statement is **true**.

4. **Statement (iv): Ca^(++) ions help in unmasking active sites on HMM.**
- **Analysis:** This statement is incorrect. Calcium ions (Ca^(++)) bind to troponin, causing a conformational change that moves tropomyosin away from the active sites on actin, thus allowing myosin to bind to actin. It does not specifically unmask active sites on heavy meromyosin (HMM).
- **Conclusion:** This statement is **false**.

### Summary of Findings:
- Statement (i): False
- Statement (ii): True
- Statement (iii): True
- Statement (iv): False

### Final Answer:
The correct options are **Statement (ii)** and **Statement (iii)**.