ISA - ISA Certified Arborist Tree Biology and Physiology 1

Question 1

In which direction does the phloem primarily transport photosynthates (sugars) within a tree?

Accepted Answer

From leaves and other sources to roots and other sinks

Answer

From roots upward to leaves via transpiration pull

Answer

Exclusively laterally through ray parenchyma cells

Answer

From the pith outward through the bark

Question 2

What is the Casparian strip, and what is its primary role in tree root physiology?

Accepted Answer

A waxy band in endodermal cells that forces water and ions to pass through cell membranes before entering the vascular cylinder

Answer

A layer of cork cells that waterproofs the root exterior

Answer

A ring of sclerenchyma fibers that provides structural support to the root

Answer

A region of meristematic cells that produces lateral roots

Question 3

What is the term for the model describing how trees limit the spread of internal decay through the formation of four distinct chemical and structural boundaries?

Accepted Answer

Compartmentalization of Decay in Trees (CODIT)

Answer

Wound wood occlusion

Answer

Lignotuber formation

Answer

Tylosis development

Question 4

Which process causes water droplets to exude from leaf hydathodes at leaf tips and margins, particularly during periods of high soil moisture and low transpiration?

Accepted Answer

Guttation driven by root pressure

Answer

Dew condensation on the leaf surface

Answer

Cavitation within the xylem vessels

Answer

Osmotic leakage from phloem sieve tubes

Question 5

What is the primary role of mycorrhizal associations in tree physiology?

Accepted Answer

To extend the effective absorptive surface area of roots and improve uptake of water and phosphorus in exchange for photosynthates

Answer

To fix atmospheric nitrogen directly into usable forms for the tree

Answer

To protect roots from soil-borne pathogens by producing antifungal compounds

Answer

To break down heartwood cellulose, releasing nutrients back into the soil

Question 6

What initiates the annual formation of a distinct abscission zone in deciduous trees, leading to autumn leaf drop?

Accepted Answer

Decreasing photoperiod (shorter days) sensed by phytochrome triggers hormonal changes that form the abscission zone

Answer

A drop in soil temperature below 10°C triggers ethylene production in roots

Answer

Frost damage to leaf mesophyll cells causes mechanical separation of the leaf

Answer

Depletion of soil nitrogen causes the tree to shed leaves to conserve nutrients