Final answer:
In a glacier ice environment, a unicellular eukaryotic organism's plasma membrane would predominantly contain unsaturated fatty acids to maintain membrane fluidity, which is crucial for cell survival in cold temperatures.
Step-by-step explanation:
The plasma membrane of a unicellular eukaryotic organism thriving in glacier ice is expected to have a predominance of unsaturated fatty acids in its phospholipids. This is because unsaturated fatty acids contain double bonds in their hydrocarbon chains, which create kinks that prevent the fatty acid tails from packing tightly together. This structural feature allows the membrane to maintain its fluidity in cold temperatures, preventing the membrane from becoming too rigid and possibly rupturing.
Phospholipids are indeed important components of the plasma membrane of cells, and in environments with fluctuating temperatures, organisms adjust the proportion of unsaturated to saturated fatty acids to maintain this necessary membrane fluidity. For example, E. coli has been observed to increase unsaturated fatty acids in its cell membrane in response to lower temperatures. Therefore, within the plasma membrane of an organism in a glacial environment, you would expect to see more unsaturated fats.