ISA Tree Biology and Physiology 3

Question 1

What is the CODIT model and who developed it?

Accepted Answer

The Compartmentalization of Decay in Trees model, developed by Dr. Alex Shigo

Answer

CODIT (Compartmentalization of Decay in Trees) was developed by Dr. Alex Shigo. It describes how trees actively wall off injured and infected tissue using four barrier walls to limit the spread of decay.

Question 2

What is the primary function of the vascular cambium in a tree?

Accepted Answer

Producing new xylem (wood) cells inward and phloem (inner bark) cells outward, enabling secondary growth

Answer

The vascular cambium is a thin layer of actively dividing meristematic cells that produces xylem toward the inside and phloem toward the outside, enabling the tree to grow in diameter.

Question 3

How do deciduous trees prepare for winter dormancy at the cellular level?

Accepted Answer

They increase sugar concentrations in cells, lower the freezing point of cytoplasm, and move water from cells to intercellular spaces where ice formation is less damaging

Answer

Cold hardening involves increasing intracellular sugar concentrations to depress the freezing point, and promoting controlled dehydration where water moves out of cells to freeze in intercellular spaces, protecting the cell membranes from ice crystal damage.

Question 4

What is the cohesion-tension theory and what process does it explain?

Accepted Answer

How water moves from roots to the top of tall trees through continuous water columns in the xylem, driven by transpiration pull

Answer

The cohesion-tension theory explains water transport in trees. Transpiration from leaf stomata creates negative pressure (tension) that pulls water upward through continuous columns in xylem vessels, held together by water's cohesive properties.

Question 5

What is the difference between heartwood and sapwood in terms of function?

Accepted Answer

Sapwood is the physiologically active outer wood that conducts water and stores reserves; heartwood is the non-conducting inner wood that provides structural support

Answer

Sapwood (outer rings) contains living ray parenchyma cells and functional xylem vessels that conduct water. Heartwood (inner rings) has undergone chemical transformation — cells are dead, vessels are blocked, but it provides critical structural support.

(ISA) ISA Certified Arborist Practice Test

(ISA) ISA Certified Arborist Practice Test

ISA Tree Biology and Physiology 3