which of the following statements is correct w.r.t. osmoregulation in Marine environment?

Options

A. entry of excess water in body followed by removal of large quantities of urine
B. optic of monovalent and divalent ions by ionocytes actively
C. loss of water from the body replenished by drinking sea water and eliminating monovalent ions actively
D. loss of divalent ions are actively through ionocytes

Answer

To solve the question regarding osmoregulation in the marine environment, we will analyze the statements provided and determine which one is correct based on our understanding of osmoregulation.

### Step-by-Step Solution:

1. **Understand Osmoregulation**:
- Osmoregulation is the process by which organisms regulate their internal osmotic pressure, balancing water and salt concentrations in their bodies.

2. **Marine Environment Characteristics**:
- In the marine environment, seawater is hypertonic, meaning it has a higher concentration of salts compared to the body fluids of marine fish, which are hypotonic (lower salt concentration).

3. **Water Movement**:
- Due to the hypertonic nature of seawater, water tends to move from the fish (hypotonic) to the seawater (hypertonic), resulting in a loss of water from the fish.

4. **Compensating for Water Loss**:
- To compensate for this water loss, marine fish drink large quantities of seawater.

5. **Salt Regulation**:
- The intake of seawater increases the salt concentration in the fish's body.
- Marine fish actively expel excess salts to maintain osmotic balance.
- Monovalent ions (like sodium and chloride) are expelled through specialized cells called ionocytes (or chloride cells) in the gills, while divalent ions (like magnesium and sulfate) are expelled through the kidneys.

6. **Analyzing the Statements**:
- **Statement A**: "Entry of excess water in body followed by removal of large quantities of urine."
- This is incorrect because marine fish lose water and produce minimal urine, not large quantities.
- **Statement B**: "Optic of monovalent and divalent ions by ionocytes actively."
- This is incorrect because while monovalent ions are expelled by ionocytes, divalent ions are expelled by the kidneys.
- **Statement C**: "Loss of water from body replenished by drinking seawater and eliminating monovalent ions actively."
- This is correct as marine fish do drink seawater to compensate for water loss and actively expel monovalent ions.
- **Statement D**: "Loss of divalent ions are actively through ionocytes."
- This is incorrect as divalent ions are expelled through the kidneys, not ionocytes.

7. **Conclusion**:
- The correct statement regarding osmoregulation in the marine environment is **Statement C**: "Loss of water from body replenished by drinking seawater and eliminating monovalent ions actively."

### Final Answer:
**C**: Loss of water from body replenished by drinking seawater and eliminating monovalent ions actively.

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