Problem 196 - Objective Biology for NEET

Question

Assertion: Growth rings are also called as annual rings. Reason: Generally the growth ring is formed in each year.

Step-by-Step Solution

Answer

Yes, the assertion is correct. Growth rings are also called annual rings because one ring is typically formed each year.

Step 1: Understand the Terms

Firstly, understand both the terms 'growth rings' and 'annual rings'. Growth rings are concentric layers that are visible in a cross-section of a tree trunk or a woody stem. Each pair of dark and light rings can represent a year in the tree's life. These are also known as annual rings

Step 2: Connect the Reason to the Assertion

Now, one can link the reason (a growth ring is formed each year) to the assertion (growth rings are also called annual rings). Since each of these rings represents a year in a tree's life, it makes sense to call them 'annual rings'.

Step 3: Confirm the Assertion

Putting it together, we can confirm the assertion based on the reason given. Because one ring is typically formed each year (hence the term 'annual'), the terms 'growth rings' and 'annual rings' can be used interchangeably. Therefore, the assertion is correct.

Key Concepts

Annual Rings

Trees have a unique way of recording their own history through growth patterns within their trunks. Known as 'growth rings' or 'annual rings,' these concentric layers tell a detailed story about a tree's age and the conditions it has endured.

Each year, typically during the growing season, trees add a layer of new growth between the bark and the wood, which we are then able to observe as rings when looking at a cross-section of the trunk. A pair of rings usually consists of a lighter ring formed during rapid spring growth and a darker ring formed in the slower growing winter season.

The thickness of these rings can provide insights into the conditions for that year. For example, a thick ring could indicate a year of plentiful resources, while a thin ring might reveal a time of drought or other stress. By counting these rings, researchers can determine not only the age of the tree but can also infer information about the historical climate and environmental conditions.

Tree's Life Cycle

The life cycle of a tree is a journey from seed to maturity and ultimately to decay, and each phase of this cycle is reflected in its growth rings. Initially, as a seedling, the tree will establish roots and begin the process of annual growth. Over the years, as the tree matures, its growth rate may fluctuate due to environmental factors like rainfall, temperature, nutrient availability, and competition for light.

During favorable years, a tree grows more vigorously, resulting in wider annual rings. Conversely, slower growth years, possibly from limited resources or harsh weather, lead to narrower rings. Eventually, as the tree reaches old age or encounters adverse conditions, growth can slow significantly, which may be evidenced by a series of very narrow rings before the tree's life ends. Understanding these patterns not only aids in aging a tree but also in studying ecological and evolutionary adaptations occur over time.

Woody Stem Cross-section

Examining the cross-section of a woody stem offers a window into a tree's structural and functional history. This cross-section reveals various layers, each playing a crucial role in the tree's growth. At the center lies the heartwood, the oldest part of the stem, providing structural support but no longer actively conducting water or nutrients.

Surrounding the heartwood is the sapwood, which is actively involved in the transport of sap. Then we encounter the growth rings, which are essentially the sapwood's historical record. The outermost layers include the cambium, a thin layer of growth tissue where new cells are produced. Beyond the cambium are the phloem and bark, responsible for nutrient transport and protection, respectively.

A thorough analysis of a tree's woody stem cross-section reveals not just the age through the growth rings but also presents a picture of the tree's health and the environmental conditions it has faced throughout its life.