ISA Certified Arborist Practice Exam

What is the primary function of tree bark?

1. To assist in photosynthesis

2. To protect the tree from physical damage and pathogens

3. To store energy

4. To transport nutrients

The correct answer is: To protect the tree from physical damage and pathogens

The primary function of tree bark is to protect the tree from physical damage and pathogens. Bark serves as the outer protective layer of a tree, safeguarding the internal tissues from environmental factors such as extreme weather, pests, diseases, and physical injuries. The bark's structure provides a barrier that helps to prevent moisture loss and serves as the first line of defense against harmful organisms. While it’s true that some bark can assist with the photosynthesis process to a limited extent, its primary role is centered around protection. Storing energy is typically a function associated with the tree’s roots and inner layers, such as the cambium and parenchyma, rather than the bark itself. The transportation of nutrients primarily occurs in the cambium (the layer of growing tissue beneath the bark) and the xylem and phloem, but bark itself does not participate in these transport functions significantly. Therefore, the focus on protection clearly defines the bark's most important role within the tree's overall functionality.