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.
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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:/npand.worpress.com/2008/08/05/tree-physics-1; and also
www.dacid1neslon.md/zadero/Trees&Capillary Action.htm