Problem 3 - Campbell Biology

Question

Heartwood and sapwood consist of (A) bark. (B) periderm. (C) secondary xylem. (D) secondary phloem.

Step-by-Step Solution

Answer

C. secondary xylem

Step 1 - Understand Key Terms: Heartwood and Sapwood

Heartwood and sapwood are parts of the woody tissue in trees. These are involved in water transport and support.

Step 2 - Determine the Functions

Heartwood is the central, non-living part of the wood which provides structural support. Sapwood is the outer, living part of the wood that carries water and nutrients.

Step 3 - Identify Components

Heartwood and sapwood are composed of the same types of tissue. Knowing their functions can help us determine which tissue is involved.

Step 4 - Eliminate Incorrect Options

Bark (option A) is the outermost layer of trees, not specifically related to heartwood or sapwood. Periderm (option B) is part of the protective layers and also not related to the water-conducting tissues. Secondary phloem (option D) is part of the bark and transports nutrients, not water.

Step 5 - Confirm the Correct Option

Secondary xylem (option C) is responsible for water conduction and structural support, found in both heartwood and sapwood.

Key Concepts

Heartwood

Heartwood is the dense, inner, non-living part of a tree's wood. It provides structural support to the tree.
As trees age, the inner cells of the sapwood become filled with chemical substances such as resins, oils, and tannins. This process turns the sapwood into heartwood.
The primary role of heartwood is to keep the tree upright and stable. It no longer participates in water transport.
Its strength and durability also make it highly sought after for furniture and construction use.

Sapwood

Sapwood is the outer, living part of the wood in a tree. It plays a critical role in transporting water and nutrients from the roots to the rest of the tree.
Unlike heartwood, sapwood is lighter in color and less dense. This is because its cells are still active in water conduction.
Sapwood functions as a nutrient pipeline, helping the tree grow and thrive. As new layers of sapwood are formed, the older sapwood gradually transforms into heartwood.

Secondary Xylem

Secondary xylem is the technical term for the wood in a tree. It is found in both heartwood and sapwood.
The main purposes of secondary xylem are to conduct water and to provide structural support. It is produced by the vascular cambium, a layer of cells between the bark and the wood.
Secondary xylem cells are elongated and have thick walls, which helps to give the tree strength. The presence of lignin in the cell walls also contributes to the tree's rigidity and resistance to decay.

Tree Structure

A tree's structure is made up of several key layers, each performing essential functions.
From the outside in, these layers include:
- Bark: The protective outer layer that shields the tree from environmental damage.
- Periderm: Part of the protective layers, also includes cork.
- Phloem: Responsible for transporting nutrients throughout the tree.
- Cambium: A thin layer of cells that produce new phloem and xylem cells.
- Xylem: Includes both secondary xylem (wood) and primary xylem, conducting water and providing support.
Each of these layers plays a part in maintaining the health and growth of the tree. Together, they ensure the tree can transport nutrients, resist damage, and stay strong and upright.