What is sapwood?

Sapwood refers specifically to the outer layers of new wood in a tree that are actively involved in the process of transporting water and nutrients. This part of the tree contains living cells and vascular tissue, which is essential for the conduction of sap from the roots to the leaves.

In contrast, the heartwood, which is the hard central part of the tree, no longer functions in conduction and primarily serves as structural support. The roots of the tree function in anchorage and water/nutrient uptake but are not considered sapwood. Lastly, while the bark of a tree plays a role in protecting the tree and can be involved in photosynthesis, the main site for photosynthesis is typically the leaves, not the wood itself.

Therefore, the option that defines sapwood accurately highlights its role in the tree's vascular system.