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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: rj1027 on October 07, 2004, 10:01:34 PM

Title: what formula would i use
Post by: rj1027 on October 07, 2004, 10:01:34 PM

This question asks for calculations and I dont know which ones to use:

the sequoia trees of northern California are the tallest trees in the world reaching over three fundred feet.  Explain how water can be transported from the roots to this height.  Support you answer with calculations?  

Title: Re:what formula would i use
Post by: Donaldson Tan on October 08, 2004, 02:25:26 PM

Hydrolysis of ATP provides energy for the active transport of water

Title: Re:what formula would i use
Post by: Demotivator on October 09, 2004, 01:18:08 AM

Nope. Active transport with ATP provides for the movement of molecules (nutrients) or ions  or protons across membranes against a concentration gradient. But If a plant had to use just atp to transport the enormous quantities of water, it would die from exhaustion!  ;D

Now it would help if rj1027 provides the context with which he asks questions, like what equations he has available as candidates to choose from. In the absence of such information I propose the following.

Water is transported through a combination of capillaty action (due to surface tension) and evaporative transpiration through the leaves which cause a pressure gradient to keep pulling the water.
The equation for capillary action is:
h=2Ycos(theta)/rgp
for water, theta is about 0, Y is surface tension = .07275 J/m2
g=9.8m/sec2,  p = density of water = 1000 kg/m3
So for  tree capillaries of r =.000015 meter, height achieved is about 1 meter.
Now, 1 meter or 3 ft does not explain a 300 ft tree. But when combined with the pull of  evaporative pressure and high cohesion of water (ie the hydrogen bonds keep water as a chain from getting pulled apart), water flows up the tree.