Model Answer
0 min readIntroduction
*Pila globosa*, commonly known as the apple snail, is a freshwater gastropod mollusk inhabiting ponds, lakes, and slow-flowing rivers. As an aquatic animal, *Pila* requires a specialized respiratory system to extract dissolved oxygen from water and release carbon dioxide. Unlike many aquatic mollusks relying solely on gills, *Pila* exhibits a dual respiratory system, possessing both a lung and gills, allowing it to survive in both submerged and aerial environments. This adaptation is crucial for its survival in fluctuating water levels and oxygen availability. Understanding the structure and function of these organs, and the mechanism of respiration, is key to comprehending the physiological adaptations of this fascinating creature.
Respiratory Organs of *Pila*
*Pila* possesses two primary respiratory organs: the lung and the gills. These organs work in conjunction to ensure efficient gas exchange.
1. The Lung
The lung is a highly vascularized cavity located within the mantle cavity. It is formed by the fusion of the right visceral mass and the right side of the mantle. Key features include:
- Mantle Cavity: This is the main respiratory chamber.
- Pulmonary Sac: A large, sac-like structure richly supplied with capillaries.
- Pneumatic Duct: A narrow opening connecting the pulmonary sac to the exterior through the pneumostome (breathing pore).
- Pneumostome: The external opening for air intake and expulsion, often located on the right side of the whorl. It can be closed by operculum.
The lung functions similarly to the lungs of terrestrial vertebrates, facilitating aerial respiration when the snail is exposed to air.
2. The Gills
The gills, also known as ctenidia, are located within the left side of the mantle cavity. They are filamentous structures richly supplied with blood vessels. Key features include:
- Gill Filaments: Numerous thin, plate-like filaments that increase the surface area for gas exchange.
- Afferent and Efferent Vessels: Blood vessels that carry deoxygenated and oxygenated blood, respectively, to and from the gills.
- Mantle Fold: The gill filaments are enclosed within a fold of the mantle, providing protection and maintaining a constant flow of water over the gills.
The gills function in aquatic respiration, extracting dissolved oxygen from the water when the snail is submerged.
Mechanism of Respiration in *Pila*
The respiratory mechanism in *Pila* is dynamic and adapts to the surrounding environment. It involves a coordinated interplay between the lung and the gills.
1. Aerial Respiration (Using the Lung)
- The snail rises to the water surface or emerges into the air.
- The pneumostome opens, allowing air to enter the pulmonary sac.
- Oxygen diffuses from the air into the blood capillaries surrounding the pulmonary sac.
- Carbon dioxide diffuses from the blood into the air within the pulmonary sac.
- The pneumostome closes, and the snail can descend back into the water.
2. Aquatic Respiration (Using the Gills)
- The snail remains submerged in water.
- Water enters the mantle cavity through the incurrent siphon.
- Water flows over the gill filaments, where oxygen is extracted and carbon dioxide is released.
- The water exits the mantle cavity through the excurrent siphon.
3. Combined Respiration
When *Pila* is partially submerged, both the lung and gills can function simultaneously. The lung provides oxygen from the air, while the gills extract oxygen from the surrounding water. This allows the snail to maintain a consistent oxygen supply even in fluctuating conditions.
Adaptations for Respiration
*Pila* exhibits several adaptations that enhance its respiratory efficiency:
- Dual Respiratory System: The presence of both lung and gills allows for flexibility in different environments.
- Highly Vascularized Respiratory Organs: Rich blood supply maximizes gas exchange.
- Large Surface Area: The filamentous structure of the gills and the extensive folding of the pulmonary sac increase the surface area for diffusion.
- Operculum: The operculum can close the pneumostome, preventing water from entering the lung and protecting it from damage.
Conclusion
In conclusion, *Pila globosa* demonstrates a remarkable adaptation to its aquatic and semi-aquatic lifestyle through its dual respiratory system. The coordinated function of the lung and gills, coupled with specialized structural features, allows for efficient gas exchange in varying environmental conditions. This dual capability is crucial for the survival of *Pila* in freshwater ecosystems characterized by fluctuating water levels and oxygen availability, highlighting the evolutionary success of this gastropod.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.