Question

In old trees, central dark coloured, non-conductingn secondary xylem is referred to as (a) heartwood (b) sapnood (c) softwood (d) hardwood.

Short answer

The correct answer is (a) heartwood.

Step-by-step solution

Understanding the Terms

The exercise provided requires knowledge of the terminology related to the anatomy of trees. Specifically, it refers to the part of the tree's secondary xylem, which is non-conducting and has a dark colour due to the deposition of organic compounds.

Identifying the Correct Term

Heartwood refers to the darker, non-conducting central part of the tree’s secondary xylem. Sapwood is the outer, living part of the secondary xylem that conducts water and nutrients. Softwood and hardwood refer to types of trees, not parts of wood anatomy specifically related to xylem.

Making the Correct Choice

Given the description in the exercise, the term 'heartwood' correctly matches the characteristics of central dark coloured, non-conducting secondary xylem in old trees.

Key concepts

Heartwood

When discussing the internal structure of trees, the term 'heartwood' refers to the innermost portion of the trunk. This core part of the tree becomes darker in color over time as it ceases to transport water and minerals. Instead, it serves a support function and often becomes filled with resins, oils, and other compounds that can repel insects and prevent decay.

Despite being non-conductive and not participating in the transport of sap, heartwood is a critical structural component. It provides strength and stability, enabling trees to grow tall and withstand environmental stresses such as wind and weight of snow or ice.

Sapwood

In contrast to heartwood, sapwood consists of the younger, outer layers of secondary xylem which actively participate in the transport of sap. The sap is composed of water and dissolved minerals, which are moved from the roots to the leaves and help in the growth and maintenance of the tree.

The sapwood is lighter in color and contains live cells. It makes up the functional part of the tree's vascular system. As a tree ages, the inner layers of sapwood will convert into heartwood, and new sapwood is formed from the cambium, a layer of actively dividing cells just beneath the bark.

Tree Anatomy

A tree's anatomy is complex and includes various structural components that perform specific functions. The primary parts of a tree include the roots that anchor the plant and absorb nutrients, the trunk that supports the tree and transports nutrients, the branches and leaves that are involved in photosynthesis, and the reproductive structures like flowers or cones.

The trunk can be further categorized into the bark, cambium, sapwood, and heartwood, each layer being vital to the tree's biology. Understanding these parts helps in identifying the role each plays in a tree's growth and survival.

Xylem Function

The xylem is a crucial component in tree anatomy responsible for the movement of water and minerals from the roots to the rest of the plant. It is made of specialized cells that form long tubes extending from the root tips to the leaves.

In addition to transport, the secondary xylem, which forms after the primary growing phase, contributes to thickening the trunk and branches, providing additional support. The xylem's combined roles of conduction and support are fundamental to the successful life history of a tree.