Question

Chilling resistant plants have more percentage of:

• A. Saturated fatty acids
• B. Unsaturated fatty acids
• C. Palmitic acid
• D. Stearic acid

Hint:

Double bonds in unsaturated fatty acids create kinks that prevent close molecular packing, keeping the cell membrane fluid and functioning at chilling temperatures.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Low-temperature stress (chilling and freezing) is a major abiotic factor that restricts the geographic distribution and productivity of crops.
When plants are exposed to low temperatures, the physical state of their cellular membranes undergoes a phase transition from a liquid-crystalline (fluid) state to a solid-gel (rigid) state.
This membrane solidification impairs the function of membrane-bound enzymes, disrupts ion transport, and causes cellular leakage, leading to physiological damage.
To survive chilling temperatures, plants must maintain membrane fluidity at low temperatures, a process known as homeoviscous adaptation.

Step 2: Detailed Explanation:
The physical fluidity of cellular membranes is primarily governed by the lipid composition of the lipid bilayer, specifically the ratio of saturated to unsaturated fatty acids.
Let us compare the properties of these fatty acids:
1. Saturated Fatty Acids (such as palmitic acid and stearic acid):
These fatty acids contain only single carbon-carbon bonds, allowing their hydrocarbon chains to pack together tightly.
Consequently, saturated lipids have high melting points and solidify easily at moderately low temperatures.
2. Unsaturated Fatty Acids (such as oleic, linoleic, and linolenic acids):
These fatty acids contain one or more double bonds in the cis configuration.
The cis double bonds introduce a rigid kink or bend in the hydrocarbon chain, preventing the lipid molecules from packing closely together.
As a result, unsaturated lipids have exceptionally low melting points and remain in a highly fluid, liquid-crystalline state even at low temperatures.
Chilling-resistant plants have evolved biochemical mechanisms to synthesize and incorporate a higher percentage of unsaturated fatty acids into their chloroplast and mitochondrial membranes.
This high unsaturation level lowers the phase transition temperature of the membranes, preventing them from solidifying and suffering structural damage when exposed to cold temperatures.
Conversely, chilling-sensitive plants (such as tropical crops like rice or tomato) contain a higher proportion of saturated fatty acids (like palmitic and stearic acids) in their membranes, making them highly susceptible to chilling injury.

Step 3: Final Answer:
Therefore, plants that exhibit chilling resistance possess a higher percentage of Unsaturated fatty acids in their cellular membranes.