Which statement best describes an annual ring?

Which statement best describes an annual ring?

• A. A layer of bark formed each year
• B. A ring of cambium around the stem
• C. A layer of wood formed by resin canals
• D. Light and dark rings due to variation in cell size during the year

Answer: (D)

Annual rings form because a tree’s growth rate changes with the seasons, producing a distinct pattern in the wood for each year. In spring, the tree makes cells that are large with thin walls (earlywood), which light in color. Later in the season, cell size decreases and walls thicken (latewood), which darkens the wood. The contrast between these light and dark zones creates a visible ring that represents one year of growth. This is why the correct description emphasizes light and dark rings caused by variation in cell size (and wall thickness) during the year. The other statements don’t describe how these rings form: bark layers accumulate outside the wood, not as a yearly ring; the cambium is a continuous layer around the stem, not an annual feature; and resin canals don’t create the annual ring pattern in wood.

Annual rings form because a tree’s growth rate changes with the seasons, producing a distinct pattern in the wood for each year. In spring, the tree makes cells that are large with thin walls (earlywood), which light in color. Later in the season, cell size decreases and walls thicken (latewood), which darkens the wood. The contrast between these light and dark zones creates a visible ring that represents one year of growth. This is why the correct description emphasizes light and dark rings caused by variation in cell size (and wall thickness) during the year.

The other statements don’t describe how these rings form: bark layers accumulate outside the wood, not as a yearly ring; the cambium is a continuous layer around the stem, not an annual feature; and resin canals don’t create the annual ring pattern in wood.