At high concentrations, ethanol disrupts cell membrane structure because it denatures proteins and increases the distance between neighbouring phospholipid molecules. Consequently, cell membranes may reduce in thickness by as much as $30\%$ and become more permeable. Yeast cells produce ethanol as a waste product of metabolism. When the ethanol concentration in their surroundings rises, yeast cells can increase the tolerance of their cell membrane to ethanol. Which statement correctly explains a response to ethanol that could account for the increase in tolerance of yeast cell membranes to ethanol?
- ADecreasing the ratio of saturated fatty acids to unsaturated fatty acids within cell membranes helps to prevent the tails of phospholipids on one side of the bilayer from sliding past the tails of phospholipids on the other side of the bilayer.
- BIncreasing the proportion of palmitoleic acid (a $\text{C}_{16}$ unsaturated fatty acid) to oleic acid (a $\text{C}_{18}$ unsaturated fatty acid) in the phospholipids of the bilayer increases the fluidity of the cell membrane.
- CActivating a cell‑signalling pathway triggers the unfolded protein response in the endoplasmic reticulum. The unfolded protein response pauses protein synthesis and initiates cell death in yeast cells with a high proportion of mis‑folded proteins.
- DIncreasing the proportion of ergosterol in the cell membrane prevents the accumulation of polar molecules, such as ethanol, within the cell. Ergosterol in yeast cells has a similar effect on membrane permeability as cholesterol in mammalian cells.