Which layer of bark is responsible for the transport of nutrients?

The phloem is the layer of bark responsible for the transport of nutrients. This tissue plays a crucial role in conveying the products of photosynthesis, such as sugars, from the leaves where they are produced, down to other parts of the tree, including the roots. The flow occurs in both directions, allowing the tree to distribute nutrients essential for growth and maintenance.

In contrast, the cambium is a layer that produces new phloem and xylem cells, contributing to the tree's growth in diameter but not directly involved in nutrient transport. The xylem, or sapwood, is primarily responsible for transporting water and minerals absorbed from the soil to the leaves and other parts of the tree. Heartwood, on the other hand, is the older, inner core of the tree trunk that no longer participates in transport; it mainly provides structural support. Thus, the phloem is specifically designated for the distribution of nutrients, making it the correct choice.