Stomata

What Are Stomata?

Stomata refers to small openings or pores mainly in plants' leaves and stems that provide gas exchange. Each stomata is bordered by two specialised cells, called guard cells, which control the stomata's opening and closing.

Stomata are essential in photosynthesis since they are responsible for taking in carbon dioxide gas and giving out oxygen gas. They can also promote cooling in plants by facilitating transpiration and allowing the flow of specific nutrients within the plant.

The structure, types, functions, mechanisms, and adaptations of stomata all help explain the importance they play in agriculture and evolution. This paper will also showcase factors that impact stomatal movement and stomatal density to provide the reader with basic knowledge through advanced understanding.

Structure Of Stomata

The structure of stomata is complex and of prime importance for its function in plant physiology. Knowledge of this structure helps in understanding how they work.

• Guard Cells: Bean-shaped cells surrounding the stomata and in charge of its opening and closing by taking different shapes.

• Stoma (Pore): This refers to the actual opening through which the gas exchange occurs.

• Accessory Cells: These are cells alongside the guard cells that support stomatal function in some plant species.

Types Of Stomata

The various types of stomata display diversity in plant species to the number and arrangement.

Classification Based on Number and Arrangement

Anisocytic

• Stomata are flanked by three subsidiary cells of unequal sizes.

• Examples include members of the family Brassicaceae, like mustard.

Anomocytic

• Stomata are surrounded by cells which are similar in size and shape.

• Commonly occurs in most dicots, for example, Sunflower.

Diacytic

• Stomata are accompanied by two subsidiary cells oriented at right angles to the guard cells.

• Commonly found in plants like members of the family Caryophyllaceae.

Paracytic

• Stomata are flanked by one or more subsidiary cells parallel to the guard cells.

• Typical in the Rubiaceae family.

Gramineous

• Specialised form occurring in grasses; guard cells are dumbbell-shaped.

• Occurs in monocots like maize and wheat.

Structure And Function Of Stomata

The stomata carry out several vital functions that are essential for the survival and growth of the plants.

Gas Exchange

• Stomata facilitate the entry of CO2 into the leaf, which is used in the process of photosynthesis.

• Permit issuance of oxygen, which is a by-product of photosynthesis.

Transpiration

• The stomata control the loss of water vapour, which in turn cools down the plant and has a role in the water balance.

Mechanism Of Stomatal Movement

The movement of stomata, i.e., opening and closing of stomata is a complicated process controlled by several factors.

Opening And Closing Mechanism

• Role of Guard Cells: The guard cells become turgid to open the stoma and flaccid to close it.

• Role of Turgor Pressure: The changes in turgor pressure in guard cells are responsible for the opening and closing of stomata.

Factors Influencing Stomatal Movement

• Stomata usually open during light to permit CO2 for photosynthesis.

• High internal CO2 closes the stomata.

• Low humidity closes the stomata to prevent loss of water.

• High temperatures raise the rate of transpiration, which can impact stomatal behaviour.

Density And Distribution Of Stomata

The stomata density and its distribution vary in different plants and are dependent on environmental and genetic factors.

Factors Affecting Stomatal Density

• Environmental Factors: Light intensity, CO2 levels, availability of water.

• Genetic Factors: Native traits in plant species.

Distribution Patterns On Leaf Surfaces

• Dorsiventral Leaves (Dicots): Stomata more on the lower surface.

• Isobilateral Leaves (Monocots): Stomata equally distributed on both surfaces.

Adaptations Of Stomata

Plants developed several stomata adaptations to adapt to different environments.

Stomata Adaptation in Different Environments

• Xerophytes: Reduced number, sunken to reduce loss of water.

• Hydrophytes: Stomata on upper surfaces for exchange of gases in water.

• Mesophytes: Stomata are evenly distributed for optimum gas exchange and water conservation.

Stomata Evolution And Plant Classification

Stomata have had a significant role in plant evolution, thus helping classify plant groups.

Evolutionary Significance Of Stomata

• Adaptation to Terrestrial Life: Enabled plants to handle loss of water while letting gasses cross through.

Stomata In Various Plant Groups

• Bryophytes: Insignificant, rather non-specialised stomata.

• Pteridophytes: More developed structures of stomata.

• Gymnosperms: Well-developed stomata to adapt to various environments.

• Angiosperm: Highly specialised stomata mirroring a wide range of habitats.

Importance Of Stomata In Agriculture

• Stomata play a very critical role in agriculture since proper functioning has direct links to crop productivity and resilience.

• Plant breeding with optimal stomatal functioning therefore holds great potential in improving water-use efficiency in crops.

• Selecting for stomatal traits that confer greater drought tolerance may lead to better performance of crops.

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