Stomata Mechanics: How a Stomata Works

Dillon Broussard (Programmer), Tobi Ray (Editor), and Brittany Schaneman (Researcher)

Humans are a species that need to seek for food, and rely on others for their food sources; however plants can make their own food through the process of photosynthesis. Photosynthesis is the chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight (Webster Dictionary). During photosynthesis the plant makes sugars which serve as a source of energy and food. This process is essential for plants to grow and live which happens when the stomata is open.

The stomata of a plant are an essential structure and are vital for photosynthesis. “The word stoma means ‘mouth’ in Greek because it allows communication between the internal and external environments of the plant” (Swarthout). The stomata are tiny pants structures found on the out later of skin, also known as the epidermis, of plants. Stomata consist of two specialized cells, also known as guard cells that surround a tiny pore called the stoma (Swarthout). The main function of the stomata is to allow gases- mainly carbon dioxide, water vapor and oxygen more rapidly in and out of the leaf of plants. They are found on all above ground parts of plants; including the petals of flowers, petioles, stems and leaves. Stomata’s are formed during the initial stages of development of the plant; therefore they reflect the environment and conditions in which they grow (Swarthout).

The mechanical interpretation of the stomata function was began in 1856 by von Mohl (Sharpe et. al.) He based his observations on six points, relating to stomatal function. According to Sharp and others in Stomatal Mechanics von Mohl six observations are:

1. Guard cells swell by the inflow of water and contract by the loss of water. The pore opens when the guard cells become turgid and closes when they become flaccid.
2. Nonuniform thickening of the guard cell wall influences the changes in cell shape as the pore opens and closes.
3. The water-extracting power (differences in osmotic potential) of guard cells in greater than that of neighboring (epidermal) cells.
4. Guard cells may have a “favorable mechanical relationship” over their surrounding cells. (Our interpretation of this statement is that von Mohl believed the guard cells possessed a mechanical advantage over the epidermal walls, and their higher turgor pressures. As was demonstration later, both theoretically and experimentally, von Mohl has this relationship exactly backwards.)
5. With the expectation of the surface along which they are in contact with the epidermal cells, guard cells may expand without restriction. (Raschke interpreted von Mohl as saying that the effect of epidermal pressure on stomatal opening depends on the ratio of the surface areas on which guard cell and epidermal pressures act. We believe that von Mohl less specific than Raschke indicated.)
6. Guard cells freed from influences of surrounding epidermal cells, as in detached strips with ruptured epidermal cells, may not behave in the same way as on undamaged leaves.

As researchers and science has become better von Mohl’s observations have been modified and restated. Science is changing and scientists are finding out more and more with stomata and how they work.

Stomata counts are critical for plant function. Smaller plants such as grasses do not have as much stomata’s as trees which have a larger mass and there for require more stomata’s for photosynthesis. Shuppan states in the article Stomatal Development,

• “Typically, the plant epidermis is tightly sealed by wax-coated, interlocking epidermal pavement cells which protect the plant body from the dry atmosphere and UV-rays. At the same time plants must be able to breathe, or exchange carbon dioxide and oxygen, for photosynthesis and respiration. Stomata act as a gateway for efficient gas exchange and water movement from the roots through the vasculature to the atmosphere.”

The stomata supplies things such as water and minerals to the entire plant system during transpiration. There are times where some plants encounter conditions such as drought; at this time a plant hormone called abscisic acid alerts the stomata to shut tightly in order to prevent plants from dehydrating and wilting (Shuppan). The stomata are crucial for a plants survival.

There are multiple parts and functions of the stomata that work during the process of photosynthesis. The specialized guard cells in the stomata of plants are called guard cells; the most important part to the stomata. Guard cells control opening and closing of the pores in the response of the environment (Shuppan). They are undersurface of leaves for controlling gas exchange and water loss of the plant. Guard cells are in pairs and shaped like a kidney bean so that stomata can exist between them. During warm weather, when a plant is likely to lose excessive water the guard cells close eliminating as much water evaporation from the interior of the leaf.

Stomatal openings are modulated by what is known as a “potassium pump” which is found in the guard cells. Ritchie states in Stomata A Window to Outside World,

• “Potassium ions (K+) contained in the guard cells influence their osmotic properties. As the K+ concentration increases, the sell osmotic potential drops. This pulls the water into the guard cells, opening the stomata.”

Photosynthesis is essential to the plant; stomata’s are critical to the process of photosynthesis. Without the stomata gasses such as carbon dioxide and oxygen could not get into the plant to make the nutrients and food the plant needs to live or the energy for the plant to grow. But without guard cells the stomata would not be able to open and close to bring in what the plant needs and keep water in. The guard cells need to work for the stomata and the stomata needs to provide a way in and out for gasses for photosynthesis to happen. Unlike humans, plants can’t hunt, gather, go to a restaurant or buy their groceries at the store; plants rely on photosynthesis to receive their essential nutrients and to grow.

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