Arborist Practice is independent and not affiliated with the International Society of Arboriculture. These are original tree biology practice questions written for study. They are not real ISA exam questions, not official ISA material, and not a substitute for the current ISA exam outline or official study materials.
Start here if tree biology is your weak domain
Free ISA tree biology practice questions are useful when you need to test the mechanics behind CODIT, cambium, xylem, phloem, branch collars, reaction wood, and wound response. This domain is small enough to study directly, but it leaks into pruning, diagnosis, risk, and construction questions. If your biology is fuzzy, other sections feel harder than they should.
Use the questions below as a focused diagnostic. Answer them without notes first. Then read the explanation even when you picked the right option. Most misses in this domain come from one of three problems: mixing up tissue functions, treating trees as if they heal like animals, or forgetting the landmarks that control proper pruning cuts.
For the concept review before or after this quiz, use the main tree biology ISA exam guide. If you want mixed-domain practice, start with the broader free ISA Certified Arborist practice questions page.
How to take this tree biology quiz
Do this as a short closed-book set:
- Give yourself 20 minutes for all 15 questions.
- Mark every answer as confident, uncertain, or guessed.
- Score only after answering the full set.
- For each miss, write the concept behind it: CODIT, vascular tissue, branch anatomy, reaction wood, roots, or physiology.
- Review the weak concept, then retake a different tree biology set later instead of memorizing these answers.
The ISA Certified Arborist exam outline is published by ISA, and ISA can update the blueprint. Use the official ISA Certified Arborist credential page and the exam outline PDF as the source of truth for current exam details.
15 ISA tree biology practice questions
1. CODIT and wound response
A branch tear exposes wood on the side of a mature tree. Over time, new tissue forms around the edge of the wound, but the exposed wood itself does not become living tissue again. Which statement best describes the tree response?
A. The tree heals the damaged wood by replacing it with new living cells
B. The tree compartmentalizes the damaged area and grows new wood around it
C. The tree moves phloem into the center of the wound to restart transport
D. The tree dissolves the damaged xylem and converts it into bark
Answer: B. Trees do not heal wounds by replacing damaged tissue the way animals do. They compartmentalize injury, resist decay spread, and grow new wood around the wound margin. That is the basic idea behind CODIT.
2. Strongest CODIT wall
Which CODIT wall is generally considered the strongest?
A. Wall 1, which resists vertical spread through vessels
B. Wall 2, which resists inward spread across growth rings
C. Wall 3, which resists lateral spread through ray cells
D. Wall 4, the new barrier zone formed after injury
Answer: D. Wall 4 is the barrier zone formed by new wood after the wound. It separates wood present at the time of injury from wood produced afterward. Wall 1 is typically the weakest.
3. Cambium function
What does the vascular cambium produce during secondary growth?
A. Xylem inward and phloem outward
B. Phloem inward and xylem outward
C. Bark inward and heartwood outward
D. Roots upward and shoots downward
Answer: A. The cambium is a thin layer of dividing cells. It produces xylem to the inside and phloem to the outside. If you reverse that order, many trunk cross-section questions become confusing.
4. Xylem and phloem
A question asks which tissue primarily transports water and dissolved minerals from roots toward the crown. Which answer is best?
A. Phloem
B. Cambium
C. Xylem
D. Periderm
Answer: C. Xylem moves water and dissolved minerals upward from the roots. Phloem transports sugars and other photosynthates from source tissues to sinks.
5. Girdling damage
A mower injury removes a continuous ring of bark and phloem around a young tree, but much of the xylem remains intact. What is the main long-term problem?
A. Water can no longer move upward through any sapwood
B. Sugars cannot move normally through the phloem to roots and other sinks
C. The tree immediately loses all apical dominance
D. Heartwood begins conducting sugars instead
Answer: B. Girdling interrupts phloem transport. Water movement through xylem may continue for a while, which is why a girdled tree can look alive before root starvation and decline become obvious.
6. Branch collar cuts
When removing a branch, why should the final cut normally stay just outside the branch collar?
A. The collar contains tissue involved in closing and compartmentalizing the wound
B. Cutting through the collar prevents all sprouting
C. The collar is dead tissue and should be removed for appearance
D. A flush cut reduces the wound surface in every case
Answer: A. The branch collar is part of the tree's natural defense and wound-closure structure. A flush cut removes tissue the tree needs for compartmentalization. A stub cut leaves tissue the tree cannot close over efficiently.
7. Branch bark ridge
A pruning diagram labels the raised line of bark on the upper side of a branch union. What is that landmark called?
A. Root flare
B. Branch bark ridge
C. Reaction zone
D. Absorbing root
Answer: B. The branch bark ridge helps locate the proper cut angle when removing a branch. Pair it with the branch collar instead of using a simple flush-to-trunk rule.
8. Sapwood vs. heartwood
Which statement best separates sapwood from heartwood?
A. Sapwood is active xylem involved in water transport; heartwood is older, mostly nonliving xylem used mainly for support
B. Sapwood is outside the bark; heartwood is the living phloem layer
C. Sapwood only exists in roots; heartwood only exists in leaves
D. Sapwood conducts sugars downward; heartwood conducts water upward
Answer: A. Sapwood is the active conducting xylem. Heartwood is older xylem with a structural role and reduced or absent conductive function.
9. Reaction wood in conifers
A conifer has a leaning stem and produces reaction wood to resist the lean. Where is compression wood usually formed?
A. On the upper side of the lean
B. On the lower side of the lean
C. Only in the phloem
D. Only at branch collars
Answer: B. Conifers form compression wood on the lower side of a leaning stem. Hardwoods typically form tension wood on the upper side. The exam can swap those directions as a distractor.
10. Apical dominance
A young tree loses its terminal leader and then develops several competing upright shoots near the top. Which concept best explains this response?
A. Soil pH buffering
B. Apical dominance being disrupted
C. Heartwood conversion
D. Wall 2 of CODIT becoming stronger
Answer: B. Apical dominance is influenced by hormones produced near the shoot tip. Removing the leader can release lateral buds and create competing shoots. That is one reason structural pruning matters when trees are young.
11. Photosynthesis source and sink
Leaves in the outer crown produce carbohydrates during photosynthesis. Which tissue moves much of that sugar to growing roots, developing shoots, and storage tissues?
A. Phloem
B. Heartwood
C. Outer bark
D. Cork cambium only
Answer: A. Phloem transports sugars from sources to sinks. In exam questions, watch whether the item asks about water and minerals or sugars and carbohydrates.
12. Root flare and trunk tissue
Why is burying the root flare during planting a tree biology problem, not only an installation problem?
A. Trunk tissue is adapted to remain buried and wet
B. Buried trunk tissue and hidden girdling roots can interfere with normal gas exchange, wound response, and root function
C. The root flare should be removed before planting
D. Burying the flare forces heartwood to become absorbing root tissue
Answer: B. The root flare is the transition zone between stem and roots. Planting too deeply can hide defects, encourage girdling roots, and create moisture and oxygen problems around tissue that should not be buried.
13. Included bark
Two codominant stems have bark trapped between them at the union. Why is this a structural concern?
A. Included bark can prevent strong wood-to-wood attachment and increase the chance of failure
B. Included bark always improves compartmentalization
C. Included bark means the tree has no cambium
D. Included bark proves the roots are dead
Answer: A. Included bark can weaken attachments because the stems do not form a strong continuous wood connection. This tree biology concept shows up again in pruning and tree risk questions.
14. Epicormic shoots
After heavy canopy reduction, a tree produces many shoots from dormant or adventitious buds along older limbs. What are those shoots commonly called?
A. Absorbing roots
B. Epicormic shoots
C. Mycorrhizae
D. Scaffold roots
Answer: B. Epicormic shoots often appear after stress, over-pruning, sudden light exposure, or loss of normal hormonal control. On the exam, they may signal stress response rather than healthy structural growth.
15. Reading the question carefully
A tree has good leaf color in early spring but declines through summer during drought. The question asks which tissue transports water from roots to leaves. Which detail should guide your answer?
A. The season, because spring growth always uses phloem for water transport
B. The transport function being asked about, because water movement points to xylem
C. The leaf color, because green leaves mean heartwood is conducting sugars
D. The drought, because drought converts phloem into xylem
Answer: B. Many tree biology questions include field context, but the tested concept may be simple. Water transport means xylem. Sugar transport means phloem. New radial growth means cambium.
Score guide
Use your score to choose the next action, not to feel good or bad about the domain.
- 13–15 correct: Tree biology is probably not your main leak. Review uncertain answers, then test pruning or diagnosis because those domains reuse this material.
- 9–12 correct: You know the language but still have concept gaps. Re-read the CODIT, cambium, and branch-collar sections, then take another focused set.
- 0–8 correct: Stop taking mixed mocks for a day. Draw a trunk cross-section, memorize the CODIT walls, and practice cut-placement diagrams before moving on.
A score from 15 questions is noisy. The useful signal is the pattern. Missing three xylem/phloem items is different from missing three branch-collar items.
What tree biology questions usually test
Tree biology questions are rarely trivia for its own sake. They usually ask you to connect structure to function:
- Wounds and decay: Does the tree heal, seal, compartmentalize, or replace tissue?
- Transport: Is the question about water and minerals, or sugars and storage?
- Growth: Which tissue produces new xylem and phloem?
- Pruning anatomy: Which cut preserves the collar and respects the branch bark ridge?
- Stress response: Is the tree reacting to lean, over-pruning, girdling, drought, or root-zone damage?
That is why this domain matters beyond one section of the exam. A pruning question about a flush cut is also a tree biology question. A risk question about weak attachments may test included bark. A diagnosis question about drought stress may test xylem function and root health.
Where to go next
If you missed CODIT, cambium, xylem, phloem, or branch collar questions, read the tree biology ISA exam guide before doing more quizzes. If you missed cut-placement questions, move to the ISA pruning exam study guide. If root flare, girdling, or establishment questions caused trouble, use the installation and establishment guide.
For a broader map, review the ISA Certified Arborist exam domains and then take mixed free ISA Certified Arborist practice questions. When your weak domains are no longer obvious, switch to a timed ISA Certified Arborist practice test so pacing and stamina become part of the measurement.
How Arborist Practice fits
Arborist Practice gives you more than a static quiz page. Use it for original ISA-style practice questions, domain practice, answer explanations, bookmarks, glossary support, timed mock exams, an AI tutor, and study analytics. The goal is simple: find the domain that is costing you points, fix it, and test again under more realistic conditions.
Start with this page if you only need a quick tree biology check. Use Arborist Practice when you need repeated reps and domain-level feedback across the full exam blueprint.
FAQ
Are these official ISA tree biology questions?
No. They are original study questions from Arborist Practice. They are not real ISA exam questions, not official ISA practice material, and not endorsed by ISA.
How many tree biology questions are on the ISA Certified Arborist exam?
ISA publishes the current domain outline through its official exam materials. Prep sites commonly describe Tree Biology as one of the ten domains and often list it near 11% of the exam, but you should confirm the current weighting in ISA's own exam outline before relying on any number.
Should I study tree biology before pruning?
Usually, yes. Tree biology explains why proper cuts, branch collars, reaction wood, decay response, and stress symptoms matter. If you understand CODIT and vascular tissue first, pruning and diagnosis questions become easier to reason through.
Is a short tree biology quiz enough for exam readiness?
No. A short quiz can expose a weak concept. It cannot measure full exam pacing, stamina, or mixed-domain readiness. Use short domain quizzes early, then move to longer mixed quizzes and timed mock exams when your weak domains are improving.