Problem 197 - Objective Biology for NEET

Question

Assertion: Heartwood is more durable than the sapwood. Reason: Heartwood contains organic compound like tannins, resins, oil, gumsaromatic substances and essential oils make it hard and more durable.

Step-by-Step Solution

Answer

The assertion and the reason are both correct and connected. Heartwood is indeed more durable than sapwood due to the presence of compounds like tannins, resins, oil, gums, aromatic substances, and essential oils.

Step 1: Understanding Heartwood and Sapwood

Heartwood and sapwood are two different types of wood in a tree. Heartwood refers to the dead, darker wood in the center, while the sapwood is the lighter, living wood near the outside. Due to the substances it contains, heartwood is usually more durable.

Step 2: Analyzing the Assertion

The assertion here is 'Heartwood is more durable than the sapwood.' Based on our understanding, it is correct because heartwood, with its organic compounds and being the dead, central part of the tree, is indeed known to be more durable than sapwood.

Step 3: Verification of the Reason

The reason is 'Heartwood contains organic compound like tannins, resins, oil, gums aromatic substances and essential oils make it hard and more durable.' This reason is valid as these are the compounds that make Heartwood more resistant to decay and pests, thereby making it harder and more durable.

Key Concepts

Durability of Heartwood

When it comes to the long-lasting quality of wood, heartwood takes the spotlight over its counterpart, sapwood. The very essence of heartwood's durability lies in its position as the innermost part of the trunk. As a tree grows, the inner layers of sapwood gradually die and become heartwood. But it's not merely being at the core that endows heartwood with durability. This transformation process involves the saturation of cells with natural preservatives such as tannins and resins.

Over time, these substances fill up the spaces in the cell walls and thus, transition the wood from a living, nutrient-carrying material to a robust, supportive structure. These compounds are incredibly unappetizing to most wood-boring insects and fungi, which typically cause decay in timber. Consequently, it's these properties that impart heartwood with a sturdiness capable of enduring numerous environmental adversities, from damp conditions to invasive pests, giving it a considerably longer lifespan than sapwood.

Organic Compounds in Heartwood

The natural chemistry of heartwood is both fascinating and vital for its application in various industries. A collage of organic compounds such as tannins, resins, essential oils, and aromatic substances not only contribute to its signature darker color but also to its superior durability. These compounds play a defensive role in the life of the tree.

Tannins

Present in heartwood, tannins are a group of chemical substances derived from phenolic acids. They are widely recognized for their ability to resist fungal and microbial attacks, safeguarding the timber from decay.

Resins

Resins are sticky substances that harden upon exposure to air. They seal off the wood, creating an unwelcoming environment for decay-causing organisms.

Essential Oils

The presence of essential oils imparts a scent that deters many insects, further fortifying the wood against infestation. By providing these natural protective properties, the organic compounds within heartwood confer it with a lifespan that can greatly surpass that of sapwood.

Differences between Heartwood and Sapwood

Heartwood and sapwood differ vastly in both function and structure within a tree. Your initial encounter with these two types of wood highlights an obvious difference in color: heartwood appears darker, whereas sapwood typically showcases a lighter hue. However, the contrasts extend beyond mere pigmentation.

The sapwood, or alburnum, resides on the outer edges of the tree and is actively involved in the transport of water and nutrients upward from the roots. It is younger, and due to its active role, it tends to be more susceptible to damage and decay. Conversely, heartwood, found at the core, is no longer involved in the tree's fluid transportation system. The cells have ceased to function in terms of nutrient transport and instead, are infused with the aforementioned organic compounds which armor the tree interiorly.

Functionally, sapwood serves the living needs of the tree, while heartwood provides structural support and protection. This natural dispositional strategy of the tree contributes to the overall health and longevity of the organism. As such, in woodworking and construction, heartwood is often sought after not only for its strength but also for its innate ability to resist the elements, making it the preferred material for outdoor projects and fine furnishings.