Which one of the following statements is correct with respect to salt water balance inside the body of living organisms

Options

A. When water is not available camels do not produce urine but store urea in tissues.
B. Salmon fish excretes lot of stored salt through gill membrane when in fresh water.
C. Paramoecium discharges concentrated salt solution by contractile vacuoles
D. The body fluids of fresh water animals are generally hypotonic to surrounding water

Answer

To determine which statement is correct regarding salt water balance in living organisms, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Osmoregulation**:
- Osmoregulation is the process by which organisms regulate the osmotic pressure of their body fluids, maintaining water content and balancing salt concentrations. This is crucial for survival in various environments.

2. **Analyzing the Options**:
- **Option A**: "When water is not available, camels do not produce urine but store urea in tissues."
- Camels are adapted to arid environments and can conserve water effectively. They produce concentrated urine and store urea in their tissues to minimize water loss. This statement is correct.

- **Option B**: "Salmon fish excretes lots of stored salt through gill membrane when in fresh water."
- Salmon are anadromous fish, meaning they live in both salt and fresh water. In fresh water, they actually uptake salts through their gills and excrete dilute urine, not excreting stored salt. This statement is incorrect.

- **Option C**: "Paramecium discharges concentrated salt solution by contractile vacuoles."
- Paramecium uses contractile vacuoles to expel excess water, not concentrated salt. They maintain osmotic balance by removing water, not salt. This statement is incorrect.

- **Option D**: "The body fluid of freshwater animals are generally hypertonic in surrounding water."
- Freshwater animals are usually hypotonic compared to their environment, meaning their body fluids have a lower concentration of solutes than the surrounding water. This statement is incorrect.

3. **Conclusion**:
- After analyzing all options, the correct statement is **Option A**: "When water is not available, camels do not produce urine but store urea in tissues."