Q.A transverse section of the trunk of a tree shows concentric rings which are known as growth rings. How are these rings formed? What are the significance of these rings?

Step 1. Explain how growth rings form. The vascular cambium's activity varies through the year in response to climatic conditions. In spring, the cambium is highly active, producing xylary elements with wide lumens and thin walls - pale, lower-density spring wood (early wood). As conditions become less favourable toward autumn/winter, cambial activity slows, producing xylary elements with narrower lumens and thicker walls - darker, higher-density autumn wood (late wood). One band of spring wood plus the adjoining band of autumn wood, both laid down within the same year, together make up one growth/annual ring, made visible to the eye by the density contrast between the two bands.

Step 2. State that not every growth ring is strictly annual. The chapter cautions that while each annual ring corresponds to one year's growth, additional 'pseudo-' or 'false-annual' rings can form within a single year if the growing season is disrupted by drought, frost, defoliation, flood, mechanical injury or biotic factors - so growth rings and annual rings, while usually the same thing, are not strictly identical concepts. …

Explain the spring-wood/autumn-wood mechanism behind ring formation, then list the significance points given in the chapter ( …

• Explaining only that rings 'show age' without also explaining the underlying spring-wood/autumn-wood mechanism that forms them. …