Certified Professional Horticulturist (CPH) Practice Exam

A process whereby plant fluids do not freeze is known as:

1. Extracellular ice formation

2. Intracellular

3. Supercooling

4. Desiccation injury

The correct answer is: Supercooling

Supercooling is the process where plant fluids remain in a liquid state below their normal freezing point, effectively preventing the formation of ice. This phenomenon occurs when the temperature drops, but the fluids do not crystallize immediately, allowing the cells to survive in subzero conditions. In plants, supercooling helps to protect cellular structures and functions during cold weather, which is essential for their survival. Supercooling is often achieved through various physiological adaptations, such as the presence of solutes that disrupt the formation of ice crystals, or through the ability to remain in a liquid state by avoiding nucleation sites where ice might form. The other processes mentioned, such as extracellular ice formation, refer to the creation of ice outside of plant cells, which can lead to cell damage. Intracellular processes involve ice forming within the cells, also resulting in cellular injury. Desiccation injury, on the other hand, relates to damage caused by lack of water rather than low temperatures. Thus, supercooling is the most appropriate term to describe the mechanism by which plant fluids resist freezing, ensuring plant survival in cold environments.