ISA Certified Arborist — Practice Exam
Tree biology: practice questions
Our ISA Certified Arborist bank has 33 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.
Question 1
After compartmentalization, where does wood decay generally take place?
- In wood present at the time of injury
- Evenly through the whole trunk
- Only in the outer bark, never in wood
- Mostly in wood formed after the injury
Show the answer
A. In wood present at the time of injury — The barrier zone tends to resist outward spread into newer wood.
Question 2
Which CODIT wall resists the vertical spread of decay?
- Wall 4
- Wall 1
- Wall 3
- Wall 2
Show the answer
B. Wall 1 — Wall 1 is the weakest, because the tree must keep vertical transport going.
Question 3
In wood, what do the rays (the radial system) mainly do?
- Produce the outer bark on the outside of the trunk
- Provide most of the tree's mechanical strength
- Move materials sideways and store reserves
- Carry water up the trunk from the roots to the leaves
Show the answer
C. Move materials sideways and store reserves — The axial system carries water long distances and gives most mechanical strength.
Question 4
What cell type is found in hardwoods but not in softwoods?
- Parenchyma cells
- Ray cells
- Tracheids
- Vessel elements (pores)
Show the answer
D. Vessel elements (pores) — This is the single most important difference between the two kinds of wood.
Question 5
In the CODIT model, which wall is the barrier zone formed after wounding?
- Wall 3
- Wall 1
- Wall 2
- Wall 4
Show the answer
D. Wall 4 — Walls 1–3 exist before wounding; wall 4 is formed by the cambium afterwards.