Q.60 If a plant is shifted to cold temperature, which of the following changes would take place in its
membrane?
(A) Ratio of unsaturated to saturated fatty acids would increase
(B) Ratio of unsaturated to saturated fatty acids would decrease
(C) Absolute amount of both fatty acids would increase keeping the ratio same
(D) Absolute amount of both fatty acids would remain unchanged

Plants shift fatty acid composition in membranes when exposed to cold temperatures to maintain fluidity and prevent damage. The correct answer to the query is option (A), where the ratio of unsaturated to saturated fatty acids increases.​

Correct Answer Explanation

Cold temperatures reduce membrane fluidity as saturated fatty acids pack tightly, risking phase transitions that impair function. Plants respond by upregulating desaturases, converting saturated fatty acids like palmitic acid to unsaturated ones such as linolenic acid, raising the unsaturated-to-saturated ratio. This adaptation lowers the phase transition temperature, preserving membrane stability in cold-tolerant species.​

Option Analysis

• (A) Ratio of unsaturated to saturated fatty acids would increase: Correct. Studies on plants like Zanthoxylum bungeanum show higher unsaturated fatty acid content under cold stress, enhancing cold resistance via increased desaturase activity.
  ​

• (B) Ratio of unsaturated to saturated fatty acids would decrease: Incorrect. Decreasing unsaturation would stiffen membranes further, exacerbating cold damage seen in sensitive plants.
  ​

• (C) Absolute amount of both fatty acids would increase keeping the ratio same: Incorrect. While total fatty acids may rise slightly, the key change is the shift toward more unsaturated forms, altering the ratio.
  ​

• (D) Absolute amount of both fatty acids would remain unchanged: Incorrect. Cold induces synthesis of additional unsaturated fatty acids, changing both amounts and proportions.​