ISA Certified Arborist Exam Prep Document
2026/2027 | Tree Biology, Pruning Standards &
Urban Forestry Practices | 200 Verified
Questions with Detailed Rationales
SECTION 1: TREE BIOLOGY
1. The primary function of the xylem tissue in a tree is to:
• A) Transport sugars from leaves to roots
• B) Transport water and minerals from roots to leaves
• C) Store starches and carbohydrates
• D) Produce new growth in the cambium layer
Correct Answer: B) Transport water and minerals from roots to leaves
Rationale: Xylem is the water-conducting tissue in trees. It transports water and
dissolved minerals from the roots upward to the leaves through the transpiration
stream. Phloem, by contrast, transports sugars (photosynthates) from the leaves
to the rest of the tree. The cambium produces new xylem and phloem cells, and
parenchyma cells are primarily involved in storage.
2. The zone of cell division in a tree root is located:
• A) Behind the root cap
• B) In the root hairs
• C) At the root tip, protected by the root cap
• D) In the mature root tissue
Correct Answer: C) At the root tip, protected by the root cap
,Rationale: The root apical meristem (zone of cell division) is located at the very tip
of the root, just behind the root cap. The root cap protects the meristem as the
root pushes through the soil. Root hairs are located in the zone of maturation
(behind the elongation zone) and are responsible for water and nutrient
absorption.
3. Which of the following is the primary function of stomata?
• A) Absorb carbon dioxide and release oxygen
• B) Absorb water from the atmosphere
• C) Store carbohydrates for winter
• D) Transport sugars from leaves to roots
Correct Answer: A) Absorb carbon dioxide and release oxygen
Rationale: Stomata are small pores on the leaf surface that regulate gas exchange.
They allow carbon dioxide (CO₂) to enter the leaf for photosynthesis and release
oxygen (O₂) and water vapor (transpiration) into the atmosphere. The stomata
open and close in response to environmental conditions (light, humidity, CO₂
concentration) to balance photosynthesis and water loss.
4. The process of photosynthesis occurs primarily in which cells?
• A) Xylem cells
• B) Phloem cells
• C) Palisade mesophyll cells
• D) Epidermal cells
Correct Answer: C) Palisade mesophyll cells
Rationale: Palisade mesophyll cells are located just below the upper epidermis of
the leaf and contain the highest concentration of chloroplasts, making them the
primary site of photosynthesis. Spongy mesophyll cells also contain chloroplasts
but have fewer than the palisade layer. Xylem and phloem are vascular tissues, not
,photosynthetic tissues. Epidermal cells generally lack chloroplasts (except in some
guard cells).
5. The heartwood of a tree is composed of:
• A) Living xylem cells that transport water
• B) Dead xylem cells that provide structural support
• C) Living phloem cells that transport sugars
• D) Dead phloem cells that form the bark
Correct Answer: B) Dead xylem cells that provide structural support
Rationale: Heartwood is the central, darker-colored wood of a tree. It is composed
of dead xylem cells that no longer transport water. These cells have been filled
with extractives (chemicals that increase resistance to decay) and provide
structural support. The living, water-conducting xylem is the sapwood, which is
located just inside the cambium.
6. The vascular cambium in a tree is responsible for producing:
• A) New xylem and phloem cells
• B) Bark and cork cells
• C) New leaves and buds
• D) Root hairs
Correct Answer: A) New xylem and phloem cells
Rationale: The vascular cambium is a lateral meristem (a layer of undifferentiated
cells) located between the xylem and phloem. It produces secondary xylem (wood)
to the inside and secondary phloem (inner bark) to the outside. This is what causes
the tree to increase in girth (diameter growth). Cork cambium (phellogen)
produces cork cells that form the outer bark.
7. What is the correct order of tissue layers from the outside of a mature tree
trunk inward?
, • A) Bark → Phloem → Cambium → Xylem → Heartwood
• B) Phloem → Cambium → Bark → Xylem → Heartwood
• C) Bark → Xylem → Cambium → Phloem → Heartwood
• D) Xylem → Cambium → Phloem → Bark → Heartwood
Correct Answer: A) Bark → Phloem → Cambium → Xylem → Heartwood
Rationale: The correct order from the outside inward is: Outer Bark (cork and cork
cambium) → Inner Bark (secondary phloem) → Vascular Cambium → Sapwood
(secondary xylem, active water conduction) → Heartwood (dead xylem, structural
support). This layered structure allows the tree to transport water and nutrients
while providing structural integrity.
8. Which of the following tree species is classified as a conifer (softwood)?
• A) Quercus alba (White Oak)
• B) Acer saccharum (Sugar Maple)
• C) Pinus strobus (Eastern White Pine)
• D) Fraxinus pennsylvanica (Green Ash)
Correct Answer: C) Pinus strobus (Eastern White Pine)
Rationale: Conifers are gymnosperms that produce cones and have needle-like or
scale-like leaves. Eastern White Pine is a classic conifer. Oaks (Quercus), Maples
(Acer), and Ashes (Fraxinus) are deciduous hardwoods (angiosperms) that lose
their leaves in winter.
9. The primary function of the root hairs on a tree root is to:
• A) Anchor the tree into the soil
• B) Increase the surface area for water and nutrient absorption
• C) Store carbohydrates for winter dormancy
• D) Produce new root growth
2026/2027 | Tree Biology, Pruning Standards &
Urban Forestry Practices | 200 Verified
Questions with Detailed Rationales
SECTION 1: TREE BIOLOGY
1. The primary function of the xylem tissue in a tree is to:
• A) Transport sugars from leaves to roots
• B) Transport water and minerals from roots to leaves
• C) Store starches and carbohydrates
• D) Produce new growth in the cambium layer
Correct Answer: B) Transport water and minerals from roots to leaves
Rationale: Xylem is the water-conducting tissue in trees. It transports water and
dissolved minerals from the roots upward to the leaves through the transpiration
stream. Phloem, by contrast, transports sugars (photosynthates) from the leaves
to the rest of the tree. The cambium produces new xylem and phloem cells, and
parenchyma cells are primarily involved in storage.
2. The zone of cell division in a tree root is located:
• A) Behind the root cap
• B) In the root hairs
• C) At the root tip, protected by the root cap
• D) In the mature root tissue
Correct Answer: C) At the root tip, protected by the root cap
,Rationale: The root apical meristem (zone of cell division) is located at the very tip
of the root, just behind the root cap. The root cap protects the meristem as the
root pushes through the soil. Root hairs are located in the zone of maturation
(behind the elongation zone) and are responsible for water and nutrient
absorption.
3. Which of the following is the primary function of stomata?
• A) Absorb carbon dioxide and release oxygen
• B) Absorb water from the atmosphere
• C) Store carbohydrates for winter
• D) Transport sugars from leaves to roots
Correct Answer: A) Absorb carbon dioxide and release oxygen
Rationale: Stomata are small pores on the leaf surface that regulate gas exchange.
They allow carbon dioxide (CO₂) to enter the leaf for photosynthesis and release
oxygen (O₂) and water vapor (transpiration) into the atmosphere. The stomata
open and close in response to environmental conditions (light, humidity, CO₂
concentration) to balance photosynthesis and water loss.
4. The process of photosynthesis occurs primarily in which cells?
• A) Xylem cells
• B) Phloem cells
• C) Palisade mesophyll cells
• D) Epidermal cells
Correct Answer: C) Palisade mesophyll cells
Rationale: Palisade mesophyll cells are located just below the upper epidermis of
the leaf and contain the highest concentration of chloroplasts, making them the
primary site of photosynthesis. Spongy mesophyll cells also contain chloroplasts
but have fewer than the palisade layer. Xylem and phloem are vascular tissues, not
,photosynthetic tissues. Epidermal cells generally lack chloroplasts (except in some
guard cells).
5. The heartwood of a tree is composed of:
• A) Living xylem cells that transport water
• B) Dead xylem cells that provide structural support
• C) Living phloem cells that transport sugars
• D) Dead phloem cells that form the bark
Correct Answer: B) Dead xylem cells that provide structural support
Rationale: Heartwood is the central, darker-colored wood of a tree. It is composed
of dead xylem cells that no longer transport water. These cells have been filled
with extractives (chemicals that increase resistance to decay) and provide
structural support. The living, water-conducting xylem is the sapwood, which is
located just inside the cambium.
6. The vascular cambium in a tree is responsible for producing:
• A) New xylem and phloem cells
• B) Bark and cork cells
• C) New leaves and buds
• D) Root hairs
Correct Answer: A) New xylem and phloem cells
Rationale: The vascular cambium is a lateral meristem (a layer of undifferentiated
cells) located between the xylem and phloem. It produces secondary xylem (wood)
to the inside and secondary phloem (inner bark) to the outside. This is what causes
the tree to increase in girth (diameter growth). Cork cambium (phellogen)
produces cork cells that form the outer bark.
7. What is the correct order of tissue layers from the outside of a mature tree
trunk inward?
, • A) Bark → Phloem → Cambium → Xylem → Heartwood
• B) Phloem → Cambium → Bark → Xylem → Heartwood
• C) Bark → Xylem → Cambium → Phloem → Heartwood
• D) Xylem → Cambium → Phloem → Bark → Heartwood
Correct Answer: A) Bark → Phloem → Cambium → Xylem → Heartwood
Rationale: The correct order from the outside inward is: Outer Bark (cork and cork
cambium) → Inner Bark (secondary phloem) → Vascular Cambium → Sapwood
(secondary xylem, active water conduction) → Heartwood (dead xylem, structural
support). This layered structure allows the tree to transport water and nutrients
while providing structural integrity.
8. Which of the following tree species is classified as a conifer (softwood)?
• A) Quercus alba (White Oak)
• B) Acer saccharum (Sugar Maple)
• C) Pinus strobus (Eastern White Pine)
• D) Fraxinus pennsylvanica (Green Ash)
Correct Answer: C) Pinus strobus (Eastern White Pine)
Rationale: Conifers are gymnosperms that produce cones and have needle-like or
scale-like leaves. Eastern White Pine is a classic conifer. Oaks (Quercus), Maples
(Acer), and Ashes (Fraxinus) are deciduous hardwoods (angiosperms) that lose
their leaves in winter.
9. The primary function of the root hairs on a tree root is to:
• A) Anchor the tree into the soil
• B) Increase the surface area for water and nutrient absorption
• C) Store carbohydrates for winter dormancy
• D) Produce new root growth
