Model Answer
0 min readIntroduction
Bryophytes, representing a transitional phase between algae and vascular plants, exhibit a distinct life cycle characterized by alternation of generations. *Anthoceros*, belonging to the class Anthocerotopsida, is a genus of hornworts known for its persistent, horn-like sporophyte. The sporophyte is the diploid, spore-producing generation and is nutritionally dependent on the gametophyte. Understanding the anatomy of the *Anthoceros* sporophyte is crucial for comprehending its role in reproduction and dispersal, and its evolutionary significance within the plant kingdom. This answer will detail the longitudinal section (LS) of the *Anthoceros* sporophyte, highlighting its key features.
Longitudinal Section of *Anthoceros* Sporophyte
The sporophyte of *Anthoceros* is a relatively simple structure, but its internal organization is vital for spore formation and release. A longitudinal section reveals three main parts: the foot, the seta, and the capsule.
1. Foot
The foot is the basal, embedded portion of the sporophyte. It anchors the sporophyte to the gametophyte and is responsible for absorbing nutrients and water from the gametophyte tissue. It lacks chlorophyll and is entirely dependent on the gametophyte for sustenance. The foot region shows a network of haustorial cells penetrating the gametophytic tissues.
2. Seta
The seta is the stalk-like structure that elevates the capsule. It is typically short and cylindrical, and its cells are elongated and contain chloroplasts, though its photosynthetic contribution is minimal. The seta’s primary function is to provide mechanical support to the capsule, positioning it for optimal spore dispersal. The seta is not uniformly thick; it often exhibits a slight swelling near the capsule.
3. Capsule
The capsule is the spore-producing organ and constitutes the major portion of the sporophyte. It is horn-shaped, hence the name "hornwort." The capsule wall is composed of a single layer of cells. Let's examine the internal structures of the capsule:
- Sporogenous Tissue: This is the central core of the capsule and is responsible for producing spores through meiosis. The sporogenous cells undergo reduction division to form haploid spores.
- Elaters: Interspersed among the spore mother cells are elaters. These are elongated, hygroscopic cells with spiral thickenings. They play a crucial role in spore dispersal. As they dry, the spiral thickenings unwind, causing the elaters to twist and jerk, scattering the spores.
- Stomata: The capsule epidermis contains numerous stomata. These pores regulate gas exchange, facilitating respiration within the capsule and aiding in the drying process necessary for elater function.
- Pseudoelaters: These are also present within the capsule, but unlike true elaters, they lack spiral thickenings. Their function is not fully understood, but they are believed to aid in spore dispersal by creating air spaces.
- Columella: A central sterile column of cells, the columella, extends through the length of the capsule, providing structural support.
Internal Capsule Structure - Detailed
The capsule's internal structure is characterized by a central sterile columella surrounded by sporogenous tissue and interspersed with elaters and pseudoelaters. The capsule wall is relatively thin, allowing for efficient spore release. The stomata are particularly abundant towards the capsule apex, facilitating rapid drying and elater activation.
| Structure | Function |
|---|---|
| Foot | Anchorage & Nutrient Absorption |
| Seta | Support for Capsule |
| Capsule | Spore Production & Dispersal |
| Sporogenous Tissue | Meiosis & Spore Formation |
| Elaters | Spore Dispersal (Hygroscopic Movement) |
| Stomata | Gas Exchange & Drying |
Conclusion
The sporophyte of *Anthoceros* represents a fascinating example of adaptation within the bryophyte lineage. Its relatively simple structure belies the sophisticated mechanisms employed for spore production and dispersal. The interplay between the foot, seta, and capsule, along with the specialized cells within the capsule, ensures successful reproduction and continuation of the species. Further research into the precise functions of pseudoelaters and the regulation of stomatal opening in *Anthoceros* will continue to refine our understanding of bryophyte evolution and ecology.
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.