Model Answer
0 min readIntroduction
Stomata are microscopic pores present on the epidermis of leaves and stems, crucial for gaseous exchange and transpiration in plants. Their structure varies considerably across different plant species, particularly within angiosperms. These variations are categorized into distinct types based on the surrounding subsidiary cells. Understanding these stomatal types provides insights into plant adaptation and evolutionary relationships. The classification, initially proposed by Metcalfe and Chalkley, helps in plant taxonomic studies and understanding physiological processes.
Types of Stomata in Angiosperms
Angiosperms exhibit four main types of stomata:
1. Cydonia Type (Apple Type)
- Surrounded by two subsidiary cells flanking the guard cells.
- Subsidiary cells are kidney-shaped.
- Common in members of the family Rosaceae (e.g., Apple, Pear).
2. Anomocytic Type (Random Type)
- Guard cells are surrounded by a variable number of subsidiary cells, appearing randomly arranged.
- Most primitive type.
- Found in dicotyledonous plants like Solanum (Potato) and Arabidopsis.
3. Dicotyledonous Type (Rubiaceous Type)
- Guard cells are surrounded by two distinct, regularly arranged subsidiary cells.
- Subsidiary cells are rectangular.
- Common in families like Rubiaceae (e.g., Coffee, Cinchona).
4. Actinocytic Type (Cruciferous Type)
- Guard cells are surrounded by several radiating subsidiary cells.
- Subsidiary cells appear star-shaped.
- Characteristic of the family Brassicaceae (e.g., Mustard, Radish).
| Stomatal Type | Subsidiary Cell Arrangement | Occurrence |
|---|---|---|
| Cydonia | Two kidney-shaped cells | Rosaceae |
| Anomocytic | Variable, random | Solanum, Arabidopsis |
| Dicotyledonous | Two rectangular cells | Rubiaceae |
| Actinocytic | Radiating, star-shaped | Brassicaceae |
Conclusion
In conclusion, the diversity in stomatal types within angiosperms reflects adaptations to varying environmental conditions and evolutionary histories. Each type, characterized by its unique arrangement of subsidiary cells, plays a vital role in regulating gas exchange and water loss. Studying these variations is crucial for understanding plant physiology, taxonomy, and responses to environmental stress. Further research into the genetic control of stomatal development could lead to strategies for improving crop resilience.
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.