Certified Professional Horticulturist (CPH) Practice Exam

What is the process called when water removed from cells during freezing is reabsorbed during thawing without injury?

1. Extracellular ice formation

2. Intracellular ice formation

3. Supercooling

4. Desiccation injury

The correct answer is: Extracellular ice formation

The correct answer refers to the process where water that was initially removed from cells during the freezing stage is safely reabsorbed when the cells thaw without leading to any damage. While the terminology in horticulture regarding freezing and thawing processes can be complex, the key here is understanding how ice formation interacts with cellular water content. Extracellular ice formation occurs when ice forms outside the cell membranes. This process allows the majority of the cellular water to exit into the intracellular space and form ice outside the cell, rather than within the cell. As a result, when temperatures begin to rise again, and thawing occurs, this water can be reabsorbed back into the cells without causing physical injury or damage due to the lack of ice formation inside the cells. This reabsorption without injury is critical for the survival of many plant tissues during freezing and thawing cycles. Understanding this concept is particularly important in horticulture when considering plant hardiness and frost resistance strategies. The other terms listed pertain to different phenomena that do not align specifically with the harmless reabsorption of water during thawing.