Difference Between Stoma and Stomata

Main Difference – Stoma vs Stomata

Stoma and stomata are the two structures mostly found on the underside of the epidermis of plant leaves. Stoma is formed by the two guard cells, which are specialized parenchyma cells found in the epidermis of plants. Stoma is involved in the gas exchange between the plant body and the external environment. The size of the stoma is regulated depending on the environmental conditions, mainly the availability of water. Carbon dioxide which is required by photosynthesis is taken up into the cell through stoma. Oxygen, which is the byproduct of photosynthesis is also released to the external environment through stoma. The main difference between stoma and stomata is that stoma is the pore, which is surrounded by two guard cells whereas stomata are the collection of stoma found inside the lower epidermis of plant leaves.

This article explains,

1. What is a Stoma
– Structure, Characteristics, Function
2. What are Stomata
– Structure, Characteristics, Function
3. What is the difference between Stoma and Stomata

What is a Stoma

Stoma is a hole found on the underside of the plant leaf, involved in the gas exchange between leaf and the external environment. It is formed by the combination of two guard cells, which are specialized parenchyma cells found in the epidermis of leaves. Guard cells are found in the epidermis of the stems as well. The hole between the two guard cells is called a stomatal pore. The size of the stomatal pore is increased with the availability of water inside the guard cells.

When water is readily available, guard cells become turgid. In contrast, when water is not available in hot and dry conditions, guard cells become flaccid. The turgor pressure of the guard cell is controlled by the water potential inside the cell. A large quantity of sugars and ions are moved into the guard cell by increasing the solute concentration inside the cell. Potassium and chloride ions are the ions which generally move into guard cells. This create a hypertonic situation in the cell, which allows more water to move into the guard cell, increasing the water potential inside the cell. The increased turgor pressure of the cell leads to swelling of the guard cell, increasing the size of the stomatal pore. This situation is called the opening of the stomatal pore.

In a water stress during hot and dry environmental conditions, ions and sugars are released from guard cells, causing the effluxing of osmotic water from guard cells. This leads to the shrinking of guard cells, closing the stomatal pore. Anion channels play a vital role in closing the stomatal pores. Chloride and malate ions are moved from guard cells through anion channels, making a hypotonic situation inside the cell, which allows the excess water to be moved out from the cell. The closing of the stomatal pore is regulated by the plant hormone, abscisic acid.

Figure 1: The opening and closing of stomatal pore

What are Stomata

Stomata are the stomal pores found on the underside of the plant leaf. Stems of the plants also contain stomata. The opening of stomata occurs in the presence of water inside the plant. Opened stomata allow the water vapor to exit from the plant. This process is called transpiration. Transpiration produces a pull on water in the xylem to move upwards inside the stem. It also allows cooling of the plant body.

Stomata are also involved in the gas exchange between the plant body and the external atmosphere. The gases involved in the photosynthesis, oxygen and carbon dioxide, are exchanged through stomata. During photosynthesis, carbon dioxide is fixed by forming glucose. Oxygen is liberated during the light reaction of photosynthesis as a byproduct. Stomata control the entry of carbon dioxide from the external atmosphere and exit of oxygen to the external atmosphere.

During hot and dry conditions, stomata are closed, preventing the gas exchange through the stomatal pores. This leads to low concentration of carbon dioxide inside the leaf of the plant, reducing the efficiency of photosynthesis in C3 plants. The reduced levels of carbon dioxide also lead to the occurrence of photorespiration as well. In contrast in C4 plants, photosynthesis becomes more efficient in low carbon dioxide concentrations by fixing carbon dioxide twice.

Figure 2: Stomata in the underside of a leaf

Definition

Stoma: Stoma is the pore in the underside of the leaves and stems of plants.

Stomata: Stomata are the collection of pores on the underside of the plant leaves.

Function

Stoma: The opening and closing of stoma are controlled by the water potential inside the guard cells.

Stomata: Stomata are involved in the gas exchange between the plant body and external atmosphere.

Conclusion

Stoma and stomata are gas exchanging structures found in the leaves and stems of plants. Stomata is the plural word of the stoma. The opening and closing of stoma are regulated by the water potential inside the guard cells. Pair of guard cells form a stoma. When the water potential is high in guard cells, the turgor pressure inside the cell is increased and the size of the stomatal pore is increased, opening the pore. While the stomata pore is opened, carbon dioxide in the external atmosphere enters into the leaf, increasing the rate of photosynthesis. Oxygen is liberated into the outer atmosphere as a byproduct of the light reaction of photosynthesis. When water potential is low, especially during hot and dry conditions, the turgor pressure of guard cells is decreased, closing the pore. This leads to the low concentrations of carbon dioxide inside the leaf, reducing the rate of photosynthesis of C3 plants. C4 plants bear mechanisms, which can overcome the low concentration of carbon dioxide. However, the main difference between stoma and stomata is their role in the photosynthesis of plant leaves.

Reference:
1. “How Do Stomata Work in Photosynthesis?” Sciencing. N.p., n.d. Web. 20 Apr. 2017.

Image Courtesy:
1. “Guard cells signals” By June Kwak, Pascal Mäser – June Kwak, University of Maryland (Public Domain) via Commons Wikimedia
2. “LeafUndersideWithStomata” By Zephyris – Own work, CC BY-SA 3.0) via Commons Wikimedia