Here's how they work:

* Location: Guard cells are located on either side of small openings on the leaf surface called stomata (singular: stoma).

* Function: Guard cells can change shape, opening and closing the stomata. This regulates the flow of gases like carbon dioxide (CO2) into the leaf for photosynthesis and oxygen (O2) out of the leaf as a byproduct of photosynthesis.

* Mechanism: The guard cells contain chloroplasts and can take in water, which makes them swell and open the stomata. When they lose water, they shrink and close the stomata. This process is influenced by factors like light intensity, carbon dioxide levels, and water availability.

Let me know if you'd like to learn more about how guard cells work!