Lesson 5.01: Tree Parts and Functions

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What is a tree? A tree is a woody plant that has a well-defined stem and a formed crown.  The tree has three major parts called the roots, the trunk and the crown.

Roots – The roots are the part of the tree that is typically found below ground.  The root system serves as an anchor and supports the tree.  The roots take up water and nutrients that are held within the soil.  The roots are also where manufactured food is stored within the plant. There are two basic types of tree roots called the tap and fibrous root system.

1. The fibrous system has many branching roots that spread throughout the soil.  An example of a fibrous root system tree is the White Oak.
2. The taproot system has one large root that grows downward from which other roots sprout laterally. An example of the taproot system is the Longleaf Pine, which is Alabama’s state tree.

View the following video clip on root cells. Click here to view the instructions for logging in to Discovery Education Streaming videos. Plant Cells: Function of Root and Leaf Cells (1:46)

Trunk– The trunk or bole is the main structural portion of the tree.  The trunk conducts nutrients and water from the roots to the manufacturing part of the tree, which is referred to as the crown.  The trunk is also the most valuable portion of the tree in terms of value to the landowner.  The trunk contains a majority of the useful wood in a tree that is turned into lumber, furniture, paper and many other forest products.  The cross-section of the trunk contains a series of rings.  These rings are sometimes called annual rings, which under normal conditions are produced each year.

Read Reading the Rings of a Tree to learn what all you can discover about a tree from its rings.

View the following video clip on trees to learn more about the trunk. Click here to view the instructions for logging in to Discovery Education Streaming videos. Life Science: Trees (3:02)

1. In larger, older trees the center of the trunk is dark in color and is referred to as heartwood.  The cells in this portion of the trunk no longer function and now only serve to give strength to the tree. 
2. The lighter-color wood outside of the heartwood is the xylem or sapwood of the tree.  This is the living portion of the tree.  This is also where nutrients and water are carried from the roots to the crown.  Remember, "Zip up the Xylem!"  Finally, the sapwood or xylem serves for storage of food that is made in the leaves.
3. The portion outside the sapwood and inside the bark is called the cambium.  The cambium is responsible for tree growth and forming annual rings. 
4. Outward from the cambium are the living cells called the inner bark or the phloem.  This plant tissue carries food that was made in the leaves down to the trunk, branches and roots.  Remember, "Flow down the Phloem!"
5. The bark is the part of the tree that protects the trunk.  It is formed by a thin layer of cells referred to as the cork cambium.

The crown is the top part of the tree that contains the branches, buds, twigs, flowers, fruit and leaves.  This is the manufacturing plant of the tree.  The major role of the crown is to contain the leaves to collect sunlight so photosynthesis can take place.  The crown also is beneficial to wildlife to serve as an area for nests.

View the following video clip to learn more on twigs and leaves. Click here to view the instructions for logging in to Discovery Education Streaming videos. Jay's Journal: Leave Us Alone (2:28)

Read How a Tree Eats, Drinks, and Breathes to learn more about the parts of a tree.

Visit Dr. Arbor's Tree Notes and explore all four sections of Dr. Arbor's Lecture to understand more about trees and how they function. The four sections include:

• Roots
• Leaves
• Trunk
• Twigs and Buds

Listen to each page as Dr. Arbor discusses and shows you how a tree functions. As you read and listen, complete the Tree Notes study guide to help prepare for your quiz.