Unit 1 - Structural Units & Functions

Lesson 9: Transport in Trees


Water is the single most important substance for tree life; all the vital life processes of a tree take place in water. 

Water is essential for tree life and it's primary use is for the transport of essential materials from roots to leaves.



Read the following to understand how trees transport water and nutrients

When a plant has enough water, there is enough water pressure (turgor force) within the cells to keep the cell walls rigid.
Without enough water, there is not enough water pressure within the cells. As a result, each cell's plasma membrane shrinks away from the cell wall. Without turgor pressure pressing against the cell wall, the cell walls collapse and the plant wilts. 

In trees and other vascular plants, water travels from the roots to the leaves. In Lesson 6 (trunks and branches), we learned about a tissue known as the xylem or sapwood. The xylem is composed of little tubes that transport water upwards.
But how does the tree pump water from the roots to the height of its highest branches? To find out, look at the image to the right.
   


Besides water, trees and plants require 13 different minerals from the soil, including nitrogen, phosphorous, and potassium.

As water is drawn upwards in the xylem through the process of transpiration, dissolved mineral nutrients from the soil are also carried to every cell in the tree or plant.




The carbohydrates produced in the leaves during the process of photosynthesis are known as organic nutrients. This food must be transported to every cell in the tree or plant, including the roots.

The phloem extends from the trunk to the branches to the leaves, where it is located very close to the photosynthetic tissue. As carbohydrates are produced, they accumulate in the phloem. Water then flows into the phloem cells through osmosis and drives the carbohydrates to areas where food energy is required.