**Explanation:**

Submerged hydrophytes are plants that grow completely or partially submerged in water. These plants have adaptations to cope with the challenges of living in an aquatic environment, including the exchange of gases.

**General Surface:**
Submerged hydrophytes exchange gases through their general surface, which includes the outer surface of their leaves, stems, and roots. The general surface of the plant is in direct contact with the surrounding water, allowing for the exchange of gases such as oxygen and carbon dioxide.

**Mechanism of Gas Exchange:**
The exchange of gases occurs through simple diffusion. Gases move from an area of higher concentration to an area of lower concentration until equilibrium is reached. The concentration of gases within the plant tissues is different from that of the surrounding water, allowing for the exchange of gases.

**Factors Affecting Gas Exchange:**
Several factors can affect the rate of gas exchange in submerged hydrophytes, including temperature, concentration gradients, and the presence of barriers such as cuticles or epidermal layers.

**Importance of Gas Exchange:**
Gas exchange is crucial for the survival of submerged hydrophytes as it allows for the uptake of oxygen necessary for respiration and the release of carbon dioxide produced during metabolic processes. Without efficient gas exchange, these plants would not be able to carry out essential physiological functions.

**Conclusion:**
In conclusion, submerged hydrophytes exchange gases through their general surface, which is in direct contact with the surrounding water. Gas exchange occurs through simple diffusion, allowing for the uptake of oxygen and the release of carbon dioxide. This mechanism is crucial for the survival of submerged hydrophytes as it enables them to carry out essential metabolic processes.

Exchange of gases occurs through general surface in submerged hydrophytes. Totally submerged plants are the true water plants or hydrophytes. Because they are truly aquatic they have the greatest number of adaptations to life in water