Take the 2-minute tour ×
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It's 100% free, no registration required.

I haven't yet found a decent explanation for how water moves throughout plants. It does seem to travel more efficiently upward than out or down. Why is that? How does it travel through the plant?

share|improve this question
add comment

1 Answer

up vote 9 down vote accepted

Most water moves up through the xylem by capillary action. Imagine dipping a pipette into a small pool of water; the water would rush up into the pipette. Or, imagine dipping the edge of a paper towel in water. The water "runs" up the paper towel. This is capillary action.

As water evaporates out of the leaves and such in higher regions of the plant, a capillary force pulls up more water. If for instance, you were to dry the top of your saturated paper towel, more water would be pulled up from the pool below to wet that top section.

As for a molecular explanation, Wikipedia has a good explanation of Cohesion-tension theory.

share|improve this answer
    
@Preecce, I heard of the capillary explanation, but what about a tall tree? Capillary action does not pull water up 100'. –  jmusser Feb 20 '12 at 14:22
2  
Indeed it does. There is tension between the weight of the water and the force of the capillary action, which they think is what limits the height of trees (nature.com/nature/journal/v428/n6985/abs/nature02417.html). Remember that the xylem is like a very, very skinny tube, so it isn't like there is a single massive column of water flowing up. With a narrow tube like that, the weight of the water builds pretty slowly. –  Preece Feb 20 '12 at 15:38
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.