Plant physiology in cold stress: Plants are killed in winter by frost primarily due to what immediate tissue-level effect? State the dominant mechanism responsible for lethal injury during freezing. Choose the correct process.

Given data

• We must identify why frost (freezing temperatures) kills plants in winter.

Concept / Approach
In most plant tissues, freezing begins in the extracellular spaces. Ice outside the cells lowers water potential and draws water out of the cytoplasm, causing severe dehydration and mechanical stress on membranes.

Step-by-step reasoning
• Extracellular ice → water efflux from cells → concentration of solutes and membrane damage.• Intracellular ice is also lethal but usually occurs after severe supercooling failure; the dominant field mechanism is dehydration due to extracellular freezing.

Common pitfalls

• Assuming enzymes are heat-denatured by cold; enzyme activity decreases but the lethal event is membrane/cell injury from dehydration/ice.
• Equating frost injury with ordinary plasmolysis; here the driver is ice-induced water withdrawal, not added solute outside the cell.

Final Answer
Extracellular ice formation causing cellular dehydration is the primary lethal mechanism.