Model Answer
0 min readIntroduction
*Polysiphonia* is a red alga belonging to the family Rhodophyceae, commonly found in marine environments. It exhibits a complex life cycle involving alternation of generations between a gametophytic phase (dominant) and a sporophytic phase. Understanding the sporophyte’s structure is vital for comprehending the reproductive strategies of red algae. The sporophyte is heterotrichous, meaning it has two distinct systems of filaments – the pericentral and the epithallial systems. A vertical section reveals the internal organization and developmental stages within the sporophyte, showcasing the characteristic features of red algal reproduction.
Structure of the *Polysiphonia* Sporophyte (V.S.)
The sporophyte develops from a diploid zygote formed after fertilization. The V.S. of the sporophyte reveals several key structures:
1. Cystocarp Development
The sporophyte originates from the cystocarp, a flask-shaped structure developed on the female gametophyte. The V.S. shows the following stages:
- Initial Stage: The zygote undergoes meiosis within the carpogonium, resulting in diploid carpospores.
- Carposporophyte Development: These carpospores germinate and develop into the carposporophyte, which remains embedded within the female gametophyte.
- Cystocarp Wall: The cystocarp is surrounded by a multilayered wall, providing protection to the developing sporophyte.
- Discharge Cells: Specialized cells within the cystocarp facilitate the release of carpospores.
2. Pericentral Filament System
This system forms the main axis of the sporophyte. A V.S. reveals:
- Central Cell: A large, central cell forms the core of the pericentral filament.
- Cortical Cells: Surrounding the central cell are smaller, cortical cells arranged in a single layer.
- Connecting Cells: These cells connect the pericentral filament to the epithallial filament system.
3. Epithallial Filament System
This system forms the outer covering of the sporophyte. A V.S. shows:
- Cuticle: An outer layer providing protection.
- Epithallial Cells: These cells are smaller and more densely packed than the cortical cells of the pericentral filament.
- Branching: The epithallial filaments exhibit branching, contributing to the overall structure of the sporophyte.
4. Carpospore Formation and Release
Within the cystocarp, carpospores mature and are eventually released through an opening called the ostiole. The V.S. shows:
- Mature Carpospores: Diploid carpospores are spherical or oval in shape.
- Ostiole: The opening through which carpospores are released.
- Discharge Mechanism: Specialized cells surrounding the ostiole aid in the release of carpospores.
5. Development into a New Gametophyte
Upon release, carpospores settle and germinate, developing into new female gametophytes, thus completing the life cycle.
Diagrammatic Representation (Conceptual - actual diagram would be hand-drawn for exam):
Imagine a diagram showing a flask-shaped cystocarp embedded in the female gametophyte. The pericentral filament extends from the base of the cystocarp, with a central cell and surrounding cortical cells. The epithallial filament covers the outer surface. Carpospores are visible within the cystocarp, and an ostiole is shown for their release.
Comparison with other Red Algal Sporophytes
| Feature | Polysiphonia | Gracilaria |
|---|---|---|
| Sporophyte Origin | Cystocarp on female gametophyte | Directly from carpospores |
| Filament System | Heterotrichous (pericentral & epithallial) | Simple filamentous |
| Cystocarp Structure | Flask-shaped with ostiole | Absent; carpospores released directly |
Conclusion
The V.S. of the *Polysiphonia* sporophyte reveals a complex and highly organized structure adapted for efficient reproduction. The heterotrichous filament system and the development within the cystocarp are characteristic features of this red alga. Understanding the sporophyte’s anatomy is crucial for appreciating the intricacies of the red algal life cycle and their evolutionary adaptations to marine environments. Further research into the genetic control of sporophyte development could provide valuable insights into algal reproduction and potential biotechnological applications.
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.