As the concentration of potassium inside guard cells increases, water enters the cell by osmosis. But why does the swollen causes the stoma to open? Does it relate to the thickness of the cell wall? If so, how?

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    – tyersome
    Feb 11, 2020 at 21:24
  • $\begingroup$ @tyersome, thank you for telling me that. However I have tried to do some research on it and I know how the concentration of potassium ions affects the cell's water potential which makes them swell or shrink.But my question is how swollen change the shape of cells and therefore open the stomata---why don't cells come more closely when swelling as they have larger volumes? ( and unfortunately I can't find the answers on the internet.) $\endgroup$
    – Emily
    Feb 12, 2020 at 13:42
  • $\begingroup$ Sorry I should have looked at that page closer, you are correct it doesn't actually answer your question. This site seems to have a reasonably clear explanation, though it doesn't address all types of stomata. Does that help? $\endgroup$
    – tyersome
    Feb 12, 2020 at 14:43

1 Answer 1


The link that @tyersome mentioned in the comment does a great job of answering your question. In the event that you read it and still have some confusion, here is a metaphor: imagine guard cells as two modeling balloons (the long kind that clowns use to make figurines) that are slightly inflated and attached together at both ends. Since they are only slightly inflated, they are able to sit flush next to each other. Now let's say you inflate the balloons. Since they are still attached to each other at both ends inflating them will cause them to bow outward and away from each other. The expansion will cause there to be space between the two balloons.

This is not a perfect analogy since guard cells have a varied amount of rigidity in their cell walls contributing to the shape when water enters. But maybe this can help you visualize the concepts introduced in the link above intuitively.


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