ISA Tree Biology & Physiology 2

Question 1

What is translocation and how does it differ from transpiration in trees?

Accepted Answer

Translocation is the movement of sugars and nutrients through the phloem; transpiration is the loss of water vapor through stomata that drives xylem water transport

Answer

Translocation moves photosynthetic products (sugars) and mobile nutrients through the phloem from source (leaves) to sink (roots, growing points). Transpiration is the evaporation of water from leaf stomata that creates the tension driving water up through the xylem.

Question 2

What is the role of stomata in tree physiology and what factors control their opening and closing?

Accepted Answer

Stomata are pores on leaf surfaces that regulate gas exchange (CO2 in, O2 and water out), controlled primarily by light, CO2 concentration, humidity, and water stress

Answer

Stomata are microscopic pores (formed by pairs of guard cells) primarily on leaf undersurfaces. They control the uptake of CO2 for photosynthesis and the loss of water through transpiration, opening and closing in response to environmental signals.

Question 3

What is the difference between ectomycorrhizae and endomycorrhizae (arbuscular mycorrhizae)?

Accepted Answer

Ectomycorrhizae form a fungal sheath around roots without penetrating cells; endomycorrhizae penetrate root cell walls to form arbuscules inside cells — both are beneficial

Answer

Ectomycorrhizae (ECM) form a fungal mantle around root tips and grow between cells (Hartig net) without penetrating cell walls. Endomycorrhizae (AM) penetrate root cell walls to form arbuscules — branched exchange structures inside cells. Both are mutualistic.

Question 4

How does girdling (complete removal of bark around the trunk) kill a tree?

Accepted Answer

It severs the phloem, preventing sugars produced in leaves from reaching the roots, causing root starvation and eventual death of the entire tree

Answer

Girdling removes the bark and phloem, severing the downward translocation pathway. Roots, deprived of sugars from photosynthesis, eventually starve and die. Without functional roots, the above-ground portions then die. Water transport through the xylem continues temporarily because the xylem (wood) is not removed.

Question 5

What is photoinhibition and how does it affect trees adapted to shade?

Accepted Answer

It is the inhibition or damage to the photosynthetic apparatus caused by excessive light intensity, particularly harmful to shade-adapted species suddenly exposed to full sun

Answer

Photoinhibition occurs when the photosynthetic apparatus receives more light energy than it can process, generating reactive oxygen species that damage chlorophyll and photosystem proteins. Shade-adapted trees are especially vulnerable to sudden exposure to intense light.

(ISA) ISA Certified Arborist Practice Test

(ISA) ISA Certified Arborist Practice Test

ISA Tree Biology & Physiology 2