What Happens When Stomata Open?


Stomata open to allow gaseous exchange between the plant and the atmosphere. Carbon dioxide uptake resumes and metabolic processes such as photosynthesis are facilitated. Loss of water vapor is no longer prevented as transpiration continues.


Stomata respond to changes in the environment by closing to protect against pollutants or to prevent water loss during dry conditions. Stomata are found in the above-ground epidermis (surface area) of plants, making diffusion of water vapor, oxygen and carbon dioxide possible. Diffusion occurs in both directions directly across the surface of the leaf.


A stomata refers to a stoma (pore) surrounded by two specialized guard cells. Guard cells shrink to allow opening of the stoma or swell in order to force the stoma shut either partially or completely.


Stomata close at night. Stomata open in daylight to accept carbon dioxide that's converted to food for energy during photosynthesis in the leaf.


The simultaneous process of transpiration (releasing water vapor) is achieved thanks to the diffusion gradient's ability to move water vapor out through the plant's surface. When the size of stomata change so does the rate of photosynthesis and transpiration because changes in the size of the stoma cause diffusion resistance and gas conductance to vary.


Plant respiration uses oxygen to break down glucose acquired through photosynthesis. Carbon dioxide is produced and energy is released in the form of ATP.

The Optimization Theory

A plant's ability to thrive depends on the stomata adapting to surroundings by changing size to achieve the most efficient exchange of carbon dioxide and water possible. Water-use efficiency refers to the ratio of photosynthesis to transpiration.


  • Encyclopedia of Earth: Stomata
Keywords: stomata, plant respiration, transpiration, photosynthesis

About this Author

A lifelong resident of Southern California, Corinna Craddock has been writing since 1993. She is a journalist for the San Diego Examiner and a columnist for, "Stay at Home Mom Answers." Her articles are also featured in "The Celebrity Cafe" magazine. She earned her B.A. in psychology from Ashford University and is currently a graduate student of forensic psychology.