Stomata and Guard Cells: The Dynamic Gatekeepers of Plant Life

Stomata and guard cells are essential structures found in the epidermis of plant leaves and stems. They play a crucial role in regulating gas exchange, controlling water loss, and facilitating the uptake of carbon dioxide for photosynthesis. In this article, we will explore the fascinating world of stomata and guard cells, examining their structure, function, and significance in plant physiology.


What are Stomata?

Stomata are small openings or pores primarily found on the surfaces of leaves and stems. They consist of two specialized cells, known as guard cells, which flank the pore opening.

Structure of Stomata

Each stoma is surrounded by two kidney-shaped guard cells. These cells are connected at their ends and create a pore-like opening between them. The stoma opening size can vary depending on the turgidity and shape of the guard cells.

Function of Stomata

  1. Gas Exchange: Stomata allow for the exchange of gases, such as carbon dioxide (CO2) and oxygen (O2), between the plant and its environment. Carbon dioxide enters the plant through the stomata, while oxygen, a byproduct of photosynthesis, exits.
  2. Transpiration: Stomata also facilitate transpiration, the process by which water vapor is released from the plant. This evaporation of water through the stomata creates a pulling force that helps transport water and nutrients from the roots to the rest of the plant.
  3. Temperature Regulation: Stomata can open or close to regulate the plant’s temperature by controlling the amount of water vapor released. When the plant is under heat stress, the stomata may close partially or completely to reduce water loss and maintain internal moisture.

Guard Cells

Structure of Guard Cells

Guard cells have a unique and specialized structure that allows them to control the opening and closing of the stomata.

  1. Kidney Shape: Guard cells are typically kidney-shaped, with a thickened inner wall and a thinner outer wall.
  2. Cell Wall Flexibility: The inner wall of guard cells contains cellulose microfibrils that are oriented radially. This arrangement allows the cell walls to stretch and change shape when turgor pressure increases or decreases.
  3. Stomatal Pore: The guard cells are connected at their ends, forming a stomatal pore. When the guard cells swell, the pore opens, and when they shrink, the pore closes.

Function of Guard Cells

The primary role of guard cells is to control the opening and closing of the stomata, regulating the exchange of gases and the loss of water in response to various environmental signals.

  1. Turgor Pressure: The opening and closing of stomata are regulated by changes in turgor pressure within the guard cells. When the guard cells absorb water and become turgid, they curve and create an opening. Conversely, when water is lost and turgor pressure decreases, the guard cells become flaccid, closing the stomatal pore.
  2. Environmental Signals: Guard cells respond to various environmental cues, including light intensity, carbon dioxide levels, humidity, and the plant’s water status. These signals trigger biochemical and ion transport processes within the guard cells, leading to changes in turgor pressure and the subsequent opening or closing of stomata.

Significance in Plant Physiology

The stomata and guard cells are crucial for plant survival and growth. They play a vital role in photosynthesis, gas exchange, and water regulation.

  1. Photosynthesis: Stomata facilitate the entry of carbon dioxide, a necessary component for photosynthesis, into the plant’s leaves. This process enables plants to convert sunlight into chemical energy, supporting their growth and development.
  2. Water Regulation: Through the controlled opening and closing of stomata, plants can regulate water loss and maintain proper hydration. This ability is particularly important in arid conditions, where plants need to conserve water while still carrying out photosynthesis.
  3. Plant Defense: Stomata can close rapidly in response to certain stimuli, such as pathogen attacks or extreme environmental conditions. This closure helps prevent the entry of harmful substances and limits the damage caused by external factors.


Stomata and guard cells are remarkable structures in plants, serving as the gatekeepers of vitalprocesses. They enable plants to balance gas exchange, regulate water loss, and optimize photosynthesis. The dynamic nature of stomata and the responsiveness of guard cells to environmental cues allow plants to adapt and thrive in various conditions. Understanding the structure and function of stomata and guard cells deepens our knowledge of plant physiology and highlights the intricate mechanisms that underlie the success of plant life on Earth.

Difference Between Stomata and Guard Cells

Stomata and guard cells are two important components involved in the regulation of gas exchange and transpiration in plants. Following are the differences between stomata and guard cells:


  1. Definition:
    • Stomata: These are small structures found on the surface of leaves, stems, and sometimes on flowers and fruit, which function as pores for the exchange of gases (mainly carbon dioxide and oxygen) and the regulation of water evaporation (transpiration).
  2. Structure:
    • Stomata: Consist of two guard cells that surround the pore. Stomata are usually found in large numbers in the leaf epidermis.
  3. Amount:
    • Stomata: Many are found on the surface of leaves and other parts of plants involved in gas exchange.
  4. Function:
    • Stomata: Regulate gas exchange with the environment, especially carbon dioxide in and oxygen out during photosynthesis, and regulate transpiration or water evaporation.
  5. Opening and Closing:
    • Stomata: Can open and close to regulate gas exchange and avoid excessive water loss.

Guard Cell:

  1. Definition:
    • Guard Cells: These are two cells that surround the stomata and regulate the opening and closing of the stomata.
  2. Structure:
    • Guard Cells: Consist of two cells placed side by side on either side of the stomata.
  3. Amount:
    • Guard Cells: There are always two guard cells adjacent to one stomata.
  4. Function:
    • Guard Cells: Responsible for controlling the opening and closing of stomata, allowing or stopping gas exchange and regulating transpiration rates.
  5. Meiosi During the Night:
    • Guard Cells: During the night, guard cells tend to meiosis, resulting in open stomata, and during the day, they can undergo mitosis, resulting in closed stomata.


  1. Function Dependencies:
    • Stomata and Guard Cells: Guard cells work together with stomata to regulate gas exchange and transpiration according to the needs of the plant.
  2. Reaction to Environment:
    • Stomata and Guard Cells: Both can respond to environmental factors such as light, humidity, and water pressure, regulating the opening and closing of stomata.
  3. Osmotic Pressure Regulation:
    • Guard Cells: Regulating osmotic pressure in guard cells can influence the opening and closing of stomata.

The role of guard cells and stomata is very important in maintaining water and gas homeostasis in plants. Guard cells regulate the opening and closing of stomata to ensure plants can photosynthesize efficiently and avoid excessive water loss.

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