How Plants Breathe: The Stimulating Story of Stomata

By Shannon McKee
Published: February 8, 2018 | Last updated: April 20, 2021 11:21:53
Key Takeaways

Evolutionary wonders, stomata are vital to plant health. Knowing how they work and what they do for the plant is important knowledge for every kind of grower.

Take a second and just breathe. Think about how you are bringing air full of oxygen into your lungs through your mouth. Now, take a drink of water and think of how that water travels through your mouth down toward your stomach. You don’t have to think about the air and water going to the right place unless something goes wrong and it slides down the wrong tube.


You may not consider the fact that plants have a mouth, but they do. Plants have many tiny openings called stomata, which is the Greek word for mouth. These microscopic openings are found on the surface of your plants and they play a significant role in your plants’ survival.

Stomata Basics

When you think about how plants draw in the essential things they need to live, you probably focus on the roots and how they bring in water and nutrients from the soil. The roots are a critical system, but there’s another way that plants bring in the essentials and that’s through their stomata. Stomata are found on the leaves of the plant in the highest concentration, but they’re also located along the stem and other parts that are above the soil. Having a large number of stomata around the entire plant assists in improving the potential of survival for plants.


These tiny openings in the surface of the leaf and other parts of the plant are where gases are exchanged. These stomata open and close to bring in the carbon dioxide that the plant needs to live and releases oxygen that other organisms, like us, need to breathe in to live. Bringing in the carbon dioxide, which is crucial to the photosynthesis process, is like the inhaling part of the process for us. The carbon dioxide is converted by sunlight shining on the plant into sugar that’s used for the plant to grow. The stomata also exhale as they release water molecules, and this process is called transpiration. Transpiration is necessary for cooling the plant, bringing in more carbon dioxide, and helping to improve the amount of nutrients the plant brings in.

Structure of Stomata

Stomata have a very straightforward structure. There are two guard cells on either side of the opening, and it is the opening itself that’s called the stoma. The guard cells open and close the stoma depending on the conditions surrounding it. Light levels, temperature, and other cues influence when the stomata are opened and closed. During the morning hours when the sun rises, the guard cells fill up with water and when they are completely full, the stoma opens. At this point, there’s the exchange of gases and the release of the water molecules.

Plants that are in dry, warmer climates are at risk of drying out from too much water loss from an open stoma. It’s a very careful balancing act for plants to keep the stomata open to bring in carbon dioxide and release the water molecules while keeping them closed for water retention. Some plants have evolved enough to leave their stomata open a slight bit to allow for the exchange of gases while minimizing the amount of water that’s lost out of the opening.


Stomata can be grouped into different types base on the number and characteristics of the surrounding cells. Examples of different types of stomata include:

  • Gramineous Stomata: The guard cells are narrow in the middle and wider at the ends. The subsidiary cells are parallel to the guard cells.

  • Anomocytic Stomata: Possess irregular shaped cells, similar to epidermal cells, that surround each stoma.

  • Anisocytic Stomata: Features include an unequal number of subsidiary cells (three) surrounding each stoma. Two of these cells are significantly larger than the third.

  • Diacytic Stomata: Stomata are surrounded by two subsidiary cells that are perpendicular to each stoma.

  • Paracytic Stomata: Two subsidiary cells are arranged parallel to the guard cells and stomatal pore.

Stomata Problems

Your plant’s stomata are vital to the health of the plant, and when stomata are unable to perform their job, the plant suffers. One way that you may be negatively impacting the stomata is by overcrowding your plants to where they’re unable to adequately function, as there’s little air circulation among the leaves with too many plants in too small a space.

Some diseases and fungal problems can also impact your stomata. Powdery mildew is one that can negatively impact your stomata to the point where your plant may die if not treated. The fungus that gives the leaves the look of having a layer of powder on them will block the stomata and the sunlight being absorbed by the leaves. This layer means that carbon dioxide isn’t being adequately brought into the plant, so the process of photosynthesis is affected.

Stomata may not be a mouth in the same sense as our mouths, but they have a function that’s just as important. Knowing what stomata are can help you to be mindful of how fascinating plants are in taking in carbon dioxide and turning it into oxygen that you can breathe. Plus, it’s helpful to understand so that overcrowding and diseases don’t block your plants from reaching their full potential.


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Written by Shannon McKee | Freelance Writer, Gardener

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Shannon McKee lives in Ohio and has been a freelance writer for several years now, including on her blog, Nicknamed by loved ones a garden hoarder over the past few years, she grows a wide variety of plants in her urban garden.

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