PLANT STOMATA: CHARACTERISTICS AND MAIN FUNCTIONS - BIOLOGY - 2024

The stoma of a plant is a pore, found in the epidermis of leaves, stems, and other organs, that facilitates gas exchange. Plants need to breathe through pores; this is possible through the stomata.

The pore is surrounded by a pair of specialized parenchyma, known as guard cells, which are responsible for regulating the opening size of the stomata.

The term stoma is usually used to refer to the entire stomatal complex, comprising the protective cells and the pore itself, which is referred to as the stomatal opening.

Air enters the plant through these openings due to the diffusion of gases; It contains carbon dioxide and oxygen, which are used in photosynthesis and respiration, respectively.

The oxygen produced as a result of photosynthesis is released into the atmosphere through these same openings. Additionally, water vapor is released into the atmosphere through the stomata in a process called perspiration.

Stomata are present in the sporophyte generation of all groups of terrestrial plants, except the hepatophytes. In vascular plants, the number, size, and distribution of stomata varies widely.

Plant stomata

Stomata are pores found in stems, leaves, and other parts of the plant, which control gas exchange. Through a microscope, stomata look like little soccer balls on the surface of plant structures.

Essentially, these structures allow carbon dioxide to enter and, along with water, carry out photosynthesis in the presence of sunlight to produce glucose.

Oxygen is released through the stomata as a waste product that results from photosynthesis. The plant also leaves behind some water vapor through a process called perspiration.

Plants that reside on land typically have thousands of stomata on the surfaces of their leaves. Most stomata are located on the underside of plant leaves, reducing their exposure to heat and drafts. In aquatic plants, the stomata are located on the upper part of their leaves.

Stomata are surrounded by two types of plant cells that differ from other plant epidermal cells. These cells are called guardian cells and subsidiary cells.

- Protective cells

They are large cells that surround the stoma and are connected on both sides. These cells enlarge and contract to open and close the stomatal pores. These also contain chloroplasts.

- Subsidiary cells

They surround and help the protective cells. They act as a barrier between the guard cells and the epidermal cells, protecting the epidermal cells against the expansion of the guard cells.

The subsidiary cells of the different types of plants exist in different shapes and sizes.

Opening and closing of stomata

Stomata are like a mouth. Just as muscles are needed around the lips to open and close the mouth, stomata also use structures.

Instead of muscles, plants have a specialized structure that opens and closes stomata, called a guard cell.

These cells pump ions, such as calcium and potassium, both into and out of the cell, causing the cell to contract and resulting in the stoma opening or closing. This movement is similar to the way muscles contract and release.

These cells work as a result of environmental triggers, which alter the turgor of the protective cells.

Turgor increases as a result of ions flowing into the guard cells, causing water to enter as well; then the stoma opens.

Conversely, when ions and water flow out of the protective cells, turgor decreases and the stoma closes.

Factors that affect turgor include light levels, water vapor, and carbon dioxide. On hot days, when water is limited and perspiration is high, the stomata usually stay closed.

Very early in the morning many plants have open stomata, as the temperature is cooler and the air is full of water vapor.

Some desert plants, such as succulents, open their stomata at night and can store carbon dioxide until the next day.

In situations where carbon dioxide and water are prevalent, the stomata can open for a long time, as the plant is photosynthesizing and has oxygen and water vapor that it needs to discard through these structures.

Stomatal function

The gas exchange that occurs when the stomata are open facilitates photosynthesis. Photosynthesis is the process by which plants convert sunlight into useful energy.

During photosynthesis, carbon dioxide is taken from the atmosphere through the stomata and oxygen is released as a waste product. Both photosynthesis and the exchange of gases that produce it are essential for the survival of a plant.

An unfortunate effect of opening stomata is that it allows water to leak. Unlike humans, plants do not need sweat to cool themselves and prefer to keep water within them.

However, since the gas exchange of photosynthesis is so vital, some loss of water through the stomata is necessary. This process of losing water is called perspiration.

Although perspiration cannot be avoided, plants can minimize their water loss by controlling how far the stoma opens, as well as what time of day it opens.

Opening the stoma when the surrounding air is more humid means that less water will evaporate from the leaves of the plant. But if the stoma opens when temperatures are warmer, more evaporation will occur.

Likewise, if a plant is already dehydrated, you can close its stomata to prevent additional water loss.

References

1. Plant stomata function (2017). Recovered from thoughtco.com
2. What is a stoma? definition and function. Recovered from study.com
3. Stoma. Recovered from wikipedia.org
4. Stomata of plants: function, definition and structure. Recovered from study.com