Friday, September 21, 2012

Rising to the Top


What lifts around 4 tons of water to a height of 300 feet every day, silently and without any moving parts?  This amazing feat is accomplished by the millions of tiny tubes called xylem, micrometers in diameter, in the trunk of the Giant Sequoia tree. Three natural processes combine to enable water (with nutrients) to reach the farthest reaches of these magnificent trees.

Capillary action: The cohesive properties of water make capillary action possible. The simple water molecule, H2O, happens to be electrically polarized, which means it acts like a tiny magnet. When a group of water molecules stick together, surface tension results. Surface tension is one reason rain drops form round shapes, or insects can glide over water. This polarity also helps water molecules adhere to certain surfaces, like glass. Conversely, water is repelled from other molecules like oil. Water in a thin glass tube hugs the interior glass surface and moves up the tube forming a meniscus.  This demonstrates what is called capillary action. The thinner the tube, the higher the water can rise. This is how water behaves in the xylem of the tree.

Adding to the strength of capillary action, trees along with all other plants are made up of cellulose, which is also polar. (Cellulose is made up of oxygen-hydrogen and hydroxyl chains. It is the hydrogen-bonding interactions between water and cellulose, with its hydroxyl side-chains  that provide an energetic gain against the gravity.) This allows the water to ‘hug’ the cellulosic part of the tree as the water climbs. In fact, trees are ‘masters of microfluids.’ The tiny tubes get narrower as the tree grows taller, allowing for water to continue climbing until its pressure decreases as it fights it own weight (gravity). This limits the height of the tree.

Two other processes contribute to the rise of water in the tree: evaporation in the leaves of the tree pulls the water up; osmosis in the roots of the tree pulls water and nutrients into the tree. All this is done without the tree making a sound or using any moving parts. In fact on a global scale, the movement of water through plants makes a major contribution to the hydrologic cycle by providing the particular pathway by which water moves from soil to the atmosphere (see Ref. below).

“Blessed is the man who trusts in the Lord. He will be like a tree planted by the water that sends out its roots by the stream.” (Jeremiah 17:7) Jesus said if we believe in him “streams of living water will flow from within.” (John 7:37)  The amazing process that occurs silently within trees, illustrates the power that is ours in Jesus Christ, as we allow the living water of his spirit to flow through us.
For more information see: ‘Transporting water to the tops of trees’ Physics Today, January 2008; Tree Physics 1: capillary action, the height of trees and the optimal placement of branches:/; and also Action.htm

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