ISA Certified Arborist Exam Prep Document
2026/2027| Tree Biology, Pruning Standards
and Urban Forest
Tree Biology & Physiology
Question 1
Which layer of cells is responsible for outward trunk growth and increased girth of
a tree?
A) Pith
B) Cambium
C) Epidermis
D) Cortex
Correct ,,,answer,,,: B
Rationale: The cambium is the thin layer of meristematic cells between the xylem
and phloem that produces new xylem (wood) and phloem (inner bark) cells,
enabling the tree to increase in diameter each year.
Question 2
What is the primary function of phloem in a tree?
A) Absorb water from the soil
B) Transport sugars (photosynthates) from leaves to other parts
C) Store nutrients for winter dormancy
D) Anchor the tree in the soil
Correct ,,,answer,,,: B
Rationale: Phloem transports the sugars produced during photosynthesis from the
leaves (sources) to other parts of the tree (sinks) such as roots, branches, and
developing tissues for growth and storage.
Question 3
When cutting through a tree with a chainsaw or drilling into a tree, in which order
would you pass through the layers?
,A) Bark, phloem, cambium, xylem
B) Xylem, cambium, phloem, bark
C) Cambium, phloem, xylem, bark
D) Bark, xylem, cambium, phloem
Correct ,,,answer,,,: A
Rationale: Starting from the outside moving inward, the layers are: bark
(protective outer layer), phloem (inner bark, transports sugars), cambium (thin
meristematic layer), and xylem (wood, transports water).
Question 4
What are mycorrhizae?
A) Collar rot fungi that attack the root flare
B) Elongated underground stems producing sucker sprouts
C) A symbiotic relationship between fungi and tree roots
D) Cells in which photosynthesis takes place
Correct ,,,answer,,,: C
Rationale: Mycorrhizae are beneficial fungi that form a symbiotic association with
tree roots. The fungi enhance the tree's water and nutrient absorption (especially
phosphorus), while the tree provides carbohydrates to the fungi.
Question 5
What is the function of xylem in a tree?
A) Transport water and minerals from roots to leaves
B) Transport sugars from leaves to roots
C) Store starches for winter
D) Protect the tree from physical damage
Correct ,,,answer,,,: A
Rationale: Xylem is the water-conducting tissue that transports water and
dissolved minerals from the roots upward to the leaves. In angiosperms
(hardwoods), the major water-conducting cells are vessel elements.
Question 6
If the terminal bud is removed during pruning, what is the likely result?
A) The tree will stop growing entirely
,B) Growth may be stimulated in lateral buds
C) The root system will die back
D) The tree will produce fewer leaves
Correct ,,,answer,,,: B
Rationale: Removing the terminal bud eliminates apical dominance, the hormonal
suppression of lateral bud growth. This stimulates lateral buds to grow, resulting in
a bushier appearance.
Question 7
What does the CODIT model describe?
A) How trees transport water under drought conditions
B) How trees compartmentalize decay after wounding
C) How trees reproduce sexually and asexually
D) How trees respond to fertilizer applications
Correct ,,,answer,,,: B
Rationale: CODIT (Compartmentalization of Decay in Trees) is the model
describing how trees respond to wounding by creating chemical and physical
barriers to compartmentalize (wall off) decay, preventing it from spreading
throughout the tree.
Question 8
Which of the following statements about tree growth rings is TRUE?
A) Growth rings are visible because of the rapid growth rate of earlywood relative
to latewood
B) Growth rings cannot be counted to approximate a tree's age
C) Only tropical trees produce visible growth rings
D) Growth rings provide no information about past growing conditions
Correct ,,,answer,,,: A
Rationale: Growth rings are visible due to the difference between earlywood
(larger, thinner-walled cells produced in spring) and latewood (smaller, thicker-
walled cells produced in summer). Counting rings approximates age, and ring
width can indicate past growing conditions.
, Question 9
The major water-conducting cells in angiosperms (hardwoods) are called:
A) Tracheids
B) Vessel elements
C) Sieve tube elements
D) Companion cells
Correct ,,,answer,,,: B
Rationale: Angiosperms have vessel elements as their primary water-conducting
cells, which are larger and more efficient than tracheids. Gymnosperms (conifers)
use tracheids for water conduction.
Question 10
Which part of the tree contains the highest concentration of fine, absorbing roots?
A) Directly under the trunk at 6-8 feet deep
B) Near the soil surface, often in the top 12 inches
C) At the drip line only
D) At depths greater than 10 feet
Correct ,,,answer,,,: B
Rationale: Most fine, absorbing roots are found in the top 6-12 inches of soil
where oxygen, water, and nutrients are most available. Roots grow where
conditions are favorable.
Tree Identification & Classification
Question 11
What is the correct way to write the scientific name for Red Oak?
A) Quercus Rubra
B) Quercus rubra
C) quercus Rubra
D) quercus rubra
Correct ,,,answer,,,: B
2026/2027| Tree Biology, Pruning Standards
and Urban Forest
Tree Biology & Physiology
Question 1
Which layer of cells is responsible for outward trunk growth and increased girth of
a tree?
A) Pith
B) Cambium
C) Epidermis
D) Cortex
Correct ,,,answer,,,: B
Rationale: The cambium is the thin layer of meristematic cells between the xylem
and phloem that produces new xylem (wood) and phloem (inner bark) cells,
enabling the tree to increase in diameter each year.
Question 2
What is the primary function of phloem in a tree?
A) Absorb water from the soil
B) Transport sugars (photosynthates) from leaves to other parts
C) Store nutrients for winter dormancy
D) Anchor the tree in the soil
Correct ,,,answer,,,: B
Rationale: Phloem transports the sugars produced during photosynthesis from the
leaves (sources) to other parts of the tree (sinks) such as roots, branches, and
developing tissues for growth and storage.
Question 3
When cutting through a tree with a chainsaw or drilling into a tree, in which order
would you pass through the layers?
,A) Bark, phloem, cambium, xylem
B) Xylem, cambium, phloem, bark
C) Cambium, phloem, xylem, bark
D) Bark, xylem, cambium, phloem
Correct ,,,answer,,,: A
Rationale: Starting from the outside moving inward, the layers are: bark
(protective outer layer), phloem (inner bark, transports sugars), cambium (thin
meristematic layer), and xylem (wood, transports water).
Question 4
What are mycorrhizae?
A) Collar rot fungi that attack the root flare
B) Elongated underground stems producing sucker sprouts
C) A symbiotic relationship between fungi and tree roots
D) Cells in which photosynthesis takes place
Correct ,,,answer,,,: C
Rationale: Mycorrhizae are beneficial fungi that form a symbiotic association with
tree roots. The fungi enhance the tree's water and nutrient absorption (especially
phosphorus), while the tree provides carbohydrates to the fungi.
Question 5
What is the function of xylem in a tree?
A) Transport water and minerals from roots to leaves
B) Transport sugars from leaves to roots
C) Store starches for winter
D) Protect the tree from physical damage
Correct ,,,answer,,,: A
Rationale: Xylem is the water-conducting tissue that transports water and
dissolved minerals from the roots upward to the leaves. In angiosperms
(hardwoods), the major water-conducting cells are vessel elements.
Question 6
If the terminal bud is removed during pruning, what is the likely result?
A) The tree will stop growing entirely
,B) Growth may be stimulated in lateral buds
C) The root system will die back
D) The tree will produce fewer leaves
Correct ,,,answer,,,: B
Rationale: Removing the terminal bud eliminates apical dominance, the hormonal
suppression of lateral bud growth. This stimulates lateral buds to grow, resulting in
a bushier appearance.
Question 7
What does the CODIT model describe?
A) How trees transport water under drought conditions
B) How trees compartmentalize decay after wounding
C) How trees reproduce sexually and asexually
D) How trees respond to fertilizer applications
Correct ,,,answer,,,: B
Rationale: CODIT (Compartmentalization of Decay in Trees) is the model
describing how trees respond to wounding by creating chemical and physical
barriers to compartmentalize (wall off) decay, preventing it from spreading
throughout the tree.
Question 8
Which of the following statements about tree growth rings is TRUE?
A) Growth rings are visible because of the rapid growth rate of earlywood relative
to latewood
B) Growth rings cannot be counted to approximate a tree's age
C) Only tropical trees produce visible growth rings
D) Growth rings provide no information about past growing conditions
Correct ,,,answer,,,: A
Rationale: Growth rings are visible due to the difference between earlywood
(larger, thinner-walled cells produced in spring) and latewood (smaller, thicker-
walled cells produced in summer). Counting rings approximates age, and ring
width can indicate past growing conditions.
, Question 9
The major water-conducting cells in angiosperms (hardwoods) are called:
A) Tracheids
B) Vessel elements
C) Sieve tube elements
D) Companion cells
Correct ,,,answer,,,: B
Rationale: Angiosperms have vessel elements as their primary water-conducting
cells, which are larger and more efficient than tracheids. Gymnosperms (conifers)
use tracheids for water conduction.
Question 10
Which part of the tree contains the highest concentration of fine, absorbing roots?
A) Directly under the trunk at 6-8 feet deep
B) Near the soil surface, often in the top 12 inches
C) At the drip line only
D) At depths greater than 10 feet
Correct ,,,answer,,,: B
Rationale: Most fine, absorbing roots are found in the top 6-12 inches of soil
where oxygen, water, and nutrients are most available. Roots grow where
conditions are favorable.
Tree Identification & Classification
Question 11
What is the correct way to write the scientific name for Red Oak?
A) Quercus Rubra
B) Quercus rubra
C) quercus Rubra
D) quercus rubra
Correct ,,,answer,,,: B
