Stomata- Definition, Types, Structure, Functions, Opening and closing of stomata

Plants have tiny pores on their leaf surface, called stomata. However, they perform a huge role in plant life processes. Let us know more about its type, functions, structure and mechanism.

Stomata- Definition, Types, Structure, Functions, Opening and closing of stomata

Like humans or any other living organism, plants also have different parts assigned to perform different functions. One such critical function is to perform the gaseous exchange. This important function is achieved by small pores, called Stomata. In this article, we will learn about the definition of stomata, its type, and its functions. Furthermore, we will be going to learn about the structure and mechanism of stomatal opening and closing.

Author – Parisa Gupta

What is Stomata?

“Stomata are the tiny pores present on leaf epidermis that are responsible for gaseous exchange in plants.”

These tiny openings present on the epidermis are easily visible under a light microscope. On a broad basis, the role of stomata is to help in the exchange of gases. Moreover, it also helps in photosynthesis and controls the transpiration rate by opening and closing the pore.

Stomata under microscope
Stomata, as seen under a microscope.

Types of stomata

Stomata are classified into five different types based on the number and characteristics of the surrounding subsidiary cells. Let us discuss each type:

Diacytic stomata

It is the type of stomata in which the subsidiary cells that are perpendicular to the guard cells, surround the stomatal pore in a leaf.

Paracytic stomata

When two subsidiary cells, which are in parallel to the stomatal pore and the guard cell, surround the stomatal pore, it forms a paracytic stoma.

Gramineous stomata

In this type of stomata, the stomatal pore possesses guard cells that are in the shape of a dumbbell and the arrangement of subsidiary cells is parallel to the guard cells.

Anomocytic stomata

In this type of stomata, the epidermal cells having a fixed shape and size, surround the stomata. Moreover, the stomata appear to be embedded in the epidermal cell.

Anisocytic stomata

When three subsidiary cells that are of equal size, surround the stomatal pore, it forms an anisocytic stoma.

stomata on leaf surface
Several stomata on the epidermal surface of leaves.

Functions of stomata

Stomata have many important functions, such as:

  1. Stomata help in the exchange of gases between the plants and the surroundings.
  2. It also helps in the removal of excess water in the form of vapor with the help of transpiration.
  3. Closing and opening of the stomata help in maintaining the moisture balance.
  4. It also helps in photosynthesis by facilitating carbon dioxide uptake and the release of oxygen.

Structure of stomata

The stomas are the minute pore present in the stomata, surrounded by a pair of guard cells. Generally, the guard cells are bean-shaped. However, the shape of the guard cells differs in monocots and dicots.

Furthermore, guard cells contain chloroplast which contains a green pigment known as chlorophyll responsible for capturing light energy.

The subsidiary cells surround the guard cells. Furthermore, these subsidiary cells are present on the epidermal surface of the plant. The function of the subsidiary cells is to protect guard cells.

guard cells and subsidiary cells of stomata
Stomata, surrounded by guard cells and subsidiary cells as seen under the miscroscope.

Opening and closing of stomata

The guard cells surrounding the stomata are responsible for the opening and closing of the stomata. The guard cells contain sugar and starch. Due to the high concentration of sugar in the guard cells, the water from the cytoplasm moves in the guard cell during the daytime and the stomata opens. During the nighttime, the sugar converts into starch, and hence, the water moves out of the guard cell and the stomata close.

Moreover, guard cells have chloroplast. So, during the daytime, they carry out photosynthesis and accumulate sugar. As a result of this, water enters the guard cell and they swell up. Consequently, the stomata open. Again, in the nighttime, the water moves out of the guard cell and they shrink, leading to the closing of stomata.

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