Stomata- Definition 

Stomata can be defined as the cell structures, looking like minute pores which are present in the epidermis of the plants. Stomata plays important role in Photosynthesis and Transpiration in plants

Stomata is also found in epidermis of leaves, stems, and other organs of the plant except the roots. These minute pores help in exchange of gasses between the plant and atmosphere. Stomata controls the transpiration rate by allowing it to open and close.

Stomata – Location

• Stomata are most common on green aerial parts of plants, particularly the leaves. Stomata can be easily seen under a light microscope .
• Thousands of these tiny little openings are located on the underside of the leaf. 
• Stomata are also found on stems, and other parts of plants except the roots. 
• In some cases, Stomata is also present in the fruits and colored petals of flower  parts such as stamens and pistils.

Stomata – Structure

• A stomata is formed by the two kidney-shaped guard cells along with an opening in the center called a pore.
• All of the gaseous exchanges, vapor exchanges, and absorption from the atmosphere take place through stomatal pores.
• The cell wall surrounding the pore is tough and flexible.
•  The stomata are bordered by a pair of specialized parenchyma cells which are the guard cells.
• Guard cells have a thick inner cell wall which is concave in shape.  
• Each guard cell consists of a large vacuole, plastids, cytoplasm containing chloroplasts and a nucleus. 
• The opening and closing of the stomata is guarded according to turgidity of guard cells.  
• The guard cells are surrounded by the subsidiary cells which act as accessory cells to guard cells and are found in the epidermis of plants.
• Between guard cells and epidermal cells are subsidiary cells that protect epidermal cells when guard cells expand during stomatal opening.
• The stomatal pore, guard cells and subsidiary cells togetherly form stomatal apparatus or  stomatal complex. 
• The stomata is scattered in the leaves of dicotyledons whereas in monocotyledons, they are arranged in parallel rows. 
• The average number of stomata is about 300 per square mm of the leaf surface. 
• More number of stomata is seen in the upper epidermis than the lower epidermis. 

Guard Cells of Stomata

Guard cells Definition

 Guard cells are crucially important functional elements of a Stomata. They are a pair of kidney-shaped cells with thick inner cell walls that form the opening of the stomata.

Characteristics Of Guard Cells

• These specialized cells surround the stomatal pore.
• They are always present in pairs.
• Guard cells are the only epidermal cells with chloroplasts.
• Along with chloroplasts, they also contain a larger proportion of protoplasm than other epidermal cells. 
• A turgid guard cell (full of water) allows gas to enter into the stomata.
• The guard cells close if they are flaccid (less water) so that air cannot exchange between them and water cannot escape.
• Thus, guard cells expand when turgid and contract when flaccid. 

Important Functions of Stomata

1. The main function of stomata is to open and close the pores in the leaves for an exchange of gasses.
2. Stomata allows the plant to take in carbon dioxide and give out oxygen for photosynthesis.
3. Stomata respond to outside conditions. 
4. When weather conditions are right for photosynthesis, stomata open wide for gas exchange.
5. When it is too dry or dark, stomata close up closed stomata prevent water loss in plants.
6. Stomata helps to expel the excess water out from the leaves in the form of water vapor.

Also Check – 8 Important Functions of the Stomata

Stomata Type

5 Main types of Stomata

There are five main types of stomata based on the subsidiary cells, their number and arrangement: 

1. Anomocytic Stomata
2. Anisocytic Stomata
3. Paracytic Stomata
4. Diacytic Stomata
5. Gramineous Stomata

1. Anomocytic Stomata or Type A 

• They are surrounded by irregularly shaped epidermal cells which are difficult to differentiate from other cells.
• These types of cells are called ranunculaceous cells or irregular-celled-type stomata.
• The guard cells are surrounded by a mix of the subsidiary and epidermal cells. 
• They are found in plants like Tridax, Citrullus etc. 

2. Anisocytic Stomata or Type B

• The stoma is surrounded by  three subsidiary cells which are unequal in size. 
• Two of these cells are significantly larger than the third.
• This is also called an unequal-celled type or cruciferous stomata.
• They are found in plants like Brassica, Sedum, etc. 

3. Paracytic Stomata or Type C

• Paracytic Stomata have two subsidiary cells which are arranged parallel to the guard cells and stomatal pore.
• The advantage of this arrangement is that it facilitates the guard cells to expand and contract. 
• They are found in members of Rubiaceae, and genera such as Vigna, etc. 

4. Diacytic Stomata or Type D

• Diacytic Stomata have two subsidiary cells which are arranged perpendicular to each stoma.
• It is  also known as caryophyllaceous or cross-walled stomata.
• They are found in Ocimum, Caryophyllaceae etc. 

5. Gramineous Stomata : 

• Gramineous Stomata consists of two dumbbell-shaped guard cells and two corresponding subsidiary cells.
•  The guard cells are narrow in the middle and wider at the ends. 
• They are found in Gramineae and Cyperaceae of monocotyledons. 

Frequently Asked Questions on Stomata

What are Stomata?

Stomata are tiny pores present in the epidermis of plants that help in the exchange of gasses between the plant and the atmosphere.

What is the role of Stomata in plants?

Stomata plays an important role in photosynthesis and transpiration in plants.

Where are Stomata located in plants?

Stomata are most commonly found on the green aerial parts of plants, particularly on leaves. They are also found on stems and other parts of the plant except for the roots.

How are Stomata structured?

Stomata are formed by two kidney-shaped guard cells with an opening in the center called a pore. The cell wall surrounding the pore is tough and flexible and the Stomata are bordered by a pair of specialized parenchyma cells. The opening and closing of the Stomata is guarded according to turgidity of guard cells.

What are guard cells?

Guard cells are a pair of kidney-shaped cells with thick inner cell walls that form the opening of the Stomata. They are crucially important functional elements of a Stomata.

What are the functions of Stomata?

The main function of Stomata is to open and close the pores in the leaves for an exchange of gasses. Stomata allows the plant to take in carbon dioxide and give out oxygen for photosynthesis. Stomata helps to expel the excess water out from the leaves in the form of water vapor.

What are the different types of Stomata?

There are five main types of Stomata based on the subsidiary cells, their number and arrangement: anomocytic Stomata, Anisocytic Stomata, Paracytic Stomata, Diacytic Stomata and gramineous Stomata.

Where are the different types of Stomata found?

Anomocytic Stomata are found in plants like Tridax and Citrullus, Anisocytic Stomata are found in plants like Brassica and Sedum, paracytic Stomata are found in members of Rubiaceae and genera such as Vigna, Diacytic Stomata are found in Ocimum and Caryophyllaceae and gramineous Stomata are found in grasses.

What is the role of subsidiary cells in Stomata?

Subsidiary cells are specialized epidermal cells that surround the guard cells in Stomata. They help to regulate the opening and closing of the Stomatal pore and also protect the epidermal cells when the guard cells expand during Stomatal opening.

Why do plants need to regulate transpiration?

Transpiration is the process by which plants lose water through their leaves. While some amount of transpiration is necessary for the plant’s survival, excessive transpiration can lead to water stress and dehydration. Therefore, plants need to regulate transpiration by opening and closing their Stomata in response to various environmental factors.

How do Stomata respond to changes in environmental conditions?

 Stomata can respond to changes in light, temperature, humidity and other factors by opening or closing their pores. For example, when light levels are high, Stomata will typically open to allow for more photosynthesis. Conversely, when light levels are low, Stomata may close to reduce water loss. Similarly, Stomata may close in response to high temperatures or low humidity to conserve water.

What is the difference between dicotyledon and monocotyledon Stomata?

 In dicotyledon plants, Stomata are scattered randomly on the upper and lower surfaces of the leaves. In monocotyledon plants, Stomata are arranged in parallel rows on the upper surface of the leaves.

Can Stomata be found in all parts of a plant?

 Stomata are typically found on the leaves and stems of plants, but are not present on the roots. In some cases, Stomata may also be present in other parts of the plant such as the fruits or colored petals of flowers.

Also Check – Mechanism of opening and Closing of the Stomata

Also Check – Stomatal Transpiration

Also Check – What is Guard Cells ? Definition,Location, Structure, Function and Diagram of Guard Cells

Also Check – Exchange of Gases in Plants