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UPSC MainsBOTANY-PAPER-I202010 Marks150 Words
Q5.

Draw a well labelled longitudinal sectional view of the structure of mature sporogonium of Anthoceros.

How to Approach

This question requires a detailed, labelled diagram of the mature sporogonium of *Anthoceros*. The answer should focus on accurately depicting the key structures – foot, seta, capsule, stomata, amphithecium, sterile jacket layer, central strand, archesporium, and spores. A clear, well-labelled diagram is paramount. Briefly mentioning the function of each labelled part will enhance the answer. The answer should be concise and directly address the question, avoiding unnecessary descriptive text.

Model Answer

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Introduction

*Anthoceros*, a member of the hornworts (Bryophyta), exhibits a unique sporophyte structure. The sporogonium, representing the diploid generation, is responsible for spore production and dispersal. Understanding its anatomy is crucial for comprehending the life cycle of bryophytes and their evolutionary significance. The mature sporogonium of *Anthoceros* is characterized by a persistent, horn-like capsule, a distinguishing feature of this genus. This diagrammatic representation will illustrate the internal and external features of this structure, highlighting its adaptations for spore formation and release.

Longitudinal Section of Mature *Anthoceros* Sporogonium

Below is a labelled diagram illustrating the structure of a mature *Anthoceros* sporogonium.

Anthoceros Sporogonium

Key Structures and their Functions:

  • Foot (a): The basal, embedded portion that absorbs nutrients from the gametophyte.
  • Seta (b): The stalk that elevates the capsule for spore dispersal.
  • Capsule (c): The elongated, horn-like structure where spores are produced.
  • Stomata (d): Pores on the capsule surface for gaseous exchange.
  • Amphithecium (e): The outer layer of the capsule wall, contributing to protection.
  • Sterile Jacket Layer (f): Protective layer surrounding the sporogenous tissue.
  • Central Strand (g): Vascular tissue extending from the foot through the seta and into the capsule.
  • Archesporium (h): A group of cells that undergo meiosis to form spores.
  • Spores (i): Haploid reproductive cells produced through meiosis.
  • Columella (j): Central sterile column providing support to the developing spores.

Detailed Explanation of Capsule Structure

The capsule of *Anthoceros* is unique due to its continued growth from a meristematic zone near its base. This allows for prolonged spore production. The capsule wall is multilayered, providing mechanical support and protection. The stomata regulate gas exchange, essential for photosynthesis within the capsule. The archesporium undergoes meiosis to produce numerous haploid spores, which are eventually released for dispersal.

Foot and Seta Function

The foot is crucial for the sporophyte's survival as it is entirely dependent on the gametophyte for nutrition. The seta serves as a conduit for nutrient transport and elevates the capsule, maximizing spore dispersal efficiency. The central strand facilitates this transport.

Conclusion

The mature sporogonium of *Anthoceros* represents a fascinating adaptation within the bryophyte life cycle. Its unique horn-like capsule and persistent growth allow for extended spore production. Understanding the structure and function of each component – from the nutrient-absorbing foot to the spore-producing capsule – is essential for appreciating the evolutionary success of hornworts and their role in plant diversity. Further research into the genetic regulation of sporophyte development in *Anthoceros* could provide valuable insights into plant evolution.

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.

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Additional Resources

Key Definitions

Sporophyte
The diploid, spore-producing phase in the life cycle of plants exhibiting alternation of generations. It arises from the fusion of gametes and produces spores through meiosis.
Gametophyte
The haploid, gamete-producing phase in the life cycle of plants exhibiting alternation of generations. It produces gametes through mitosis.

Key Statistics

Bryophytes, including hornworts like *Anthoceros*, are estimated to comprise approximately 20,000 species globally.

Source: Raven, P.H., Evert, R.F., & Eichhorn, S.E. (2013). Biology of Plants (8th ed.). W.H. Freeman and Company.

Approximately 100 species of hornworts are currently recognized worldwide, with *Anthoceros* being one of the most widespread genera.

Source: Hill, M.O., & Preston, J.M. (2019). Bryophytes and Climate Change. Springer.

Examples

Hornworts in Ecosystems

*Anthoceros* and other hornworts often colonize disturbed habitats, such as recently burned areas or exposed soil, contributing to soil stabilization and nutrient cycling.

Frequently Asked Questions

▶What is the significance of the persistent growth of the *Anthoceros* capsule?

The persistent growth allows for continued spore production over an extended period, increasing the chances of successful dispersal and colonization.

Topics Covered

BotanyBryophytesHornwortsSporophytesAnatomy
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