A scientist wanted to genetically engineer a new type of corn plant that could withstand cold temperatures. He decided to try to change the composition of the plant's membrane to lower the temperature of phase transition. Which of the following membrane changes might be expected to improve the cold tolerance of the plants ?

Options

A. Increasing the length of the fatty acyl chains.
B. Eliminating all steroids.
C. Increasing the frequiency of unsaturated fatty acyl chains.
D. Decreasing the frequency of unsaturated fatty acyl chains.

Explanation

To address the question regarding the genetic engineering of a corn plant to improve its cold tolerance through membrane composition changes, we can break down the solution into the following steps:

### Step 1: Understand Membrane Composition
The cell membrane is primarily composed of phospholipids, which consist of fatty acyl chains. The nature of these chains (saturated vs. unsaturated) affects the fluidity and phase transition of the membrane.

**Hint:** Consider how the structure of fatty acids influences the physical properties of the membrane.

### Step 2: Phase Transition and Temperature
At low temperatures, membranes tend to enter a gel-like phase, characterized by high viscosity. Conversely, at high temperatures, membranes become more fluid, exhibiting lower viscosity. The transition temperature at which the membrane shifts from a gel-like state to a more fluid state is known as the phase transition temperature.

**Hint:** Think about how temperature affects the state of the membrane and what changes could help maintain fluidity at lower temperatures.

### Step 3: Role of Unsaturated Fatty Acids
Unsaturated fatty acids contain one or more double bonds in their carbon chains, which introduce kinks in the structure. These kinks prevent the fatty acids from packing closely together, thereby maintaining membrane fluidity even at lower temperatures.

**Hint:** Reflect on how the presence of double bonds in fatty acids can influence the packing of lipids in the membrane.

### Step 4: Evaluate the Options
Now, let’s analyze the given options:
- **a. Increasing the length of the fatty acyl chains**: Longer chains can lead to increased van der Waals forces, potentially making the membrane less fluid at low temperatures.
- **b. Eliminating all steroids**: Steroids (like cholesterol) help maintain membrane fluidity; eliminating them could worsen cold tolerance.
- **c. Increasing the frequency of unsaturated fatty acyl chains**: This would increase the number of kinks in the fatty acid chains, enhancing fluidity and lowering the phase transition temperature, thus improving cold tolerance.
- **d. Decreasing the frequency of unsaturated fatty acyl chains**: This would make the membrane more rigid and less tolerant to cold.

**Hint:** Consider which option would allow the membrane to remain more fluid at lower temperatures.

### Step 5: Conclusion
Based on the analysis, the best option to improve the cold tolerance of the corn plant by altering the membrane composition is **c. Increasing the frequency of unsaturated fatty acyl chains**. This change would help maintain membrane fluidity at lower temperatures, preventing solidification and allowing the plant to withstand cold conditions.

**Final Answer:** Option C - Increasing the frequency of unsaturated fatty acyl chains.