The Evolution of Stomata in Land Plants

The Evolution of Stomata in Land Plants - The Evolution of...

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The Evolution of Stomata in Land Plants Emmanuelle Bailey-Greene General Biology II Professor Ejiofor Fall 2011 Contents I. Introduction II. Background III. The First Stomata IV. The Move to Land V. Modern Diversity VI. Conclusion VII. Literature Cited Introduction
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Stomata are tiny pores located in the endodermis of plant leaves and, to a lesser extent, stems. They control gas exchange, allowing carbon dioxide to enter the plant while also releasing water. The delicate balance between the two processes played a large role adaptation to the evolutionary move to land by many plants, beginning in the Silurian Period of the Paleozoic Era. This paper will investigate the evolutionary development of stomata in relation to the evolutionary development of land plants, focusing on the changes in density and placement of stomata throughout the course of history. In addition, this paper will explore the relationship between some of Earth’s various habitats and the development of stomata as a necessary physiological component of nearly all land plants. Background Stomata are pores in plants that work primarily to balance the rate of transpiration with the rate of uptake for carbon dioxide. They exist microscopically in the epidermis of plants and are surrounded by two guard cells that regulate the opening and closing of the pores in response to various stimuli. These stimuli include “carbon dioxide concentration, humidity, blue and red light, and the plant hormone abscisic acid” (Withers et al ., 2011). According to Peterson et al . (2010), each stoma is surrounded by two guard cells that control the opening and closing of the pore. Not only are these cells symmetrical, but they also operate by changes in turgor pressure. When a plant is placed into an aquatic environment, the guard cells will constrict, opening the stomata and allowing an intake of water. Conversely, if the plant were to be placed in a dry environment, the 2
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guard cells will expand, closing the stomata and putting the plant into a state where water conservation is a priority. This system creates a virtually perfect system by which a plant can have a beneficial rate of transpiration and water intake. The First Stomata According to Berry et al (2010), the earliest stomata-like plant parts have been discovered in fossils approximately 418 million years old in the extinct genus Cooksonia . Some aquatic, microscopic plant life formed symbiotic relationships with fungi that had the ability to travel toward land to absorb minerals from soil. However, when plants began the move to land approximately 400 million years ago, it was more beneficial for the plants to directly absorb the minerals from the soil.
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