2.) The phospholipid membranes of many pikilotherms have more unsaturated fatty acid tails than the membranes of homeotherms. This is an adaptaion to colder environments. Poikilotherms also have more cholesterol in their membranes, which helps the organism maintain its membrane's viscosity/fluidity both in warm and cool environments.
3.) Poikilothermic cell membrane composition is so important because poikilothermic organisms cannot self-regulate body temperature. To ensure the survival of the organism, its cells must be able to adjust to a range of temperatures. If an organism's cell membranes couldn't remain fluid at cold temperatures, its permeability would lower and certain membrane proteins would be unable to function, resulting in the possible failure of cell metabolism. Problems would also occur if the cell membrane became too fluid.
4.) One adaptation of poikilotherms involves fatty acids. When their environment is cool, poikilotherms can unsaturate the fatty acids of their cells' phospholipid membranes, preventing the membrane from becoming too rigid by increasing permeability. The opposite occurs when the environment is too warm. Another adpataion involves cholesterol. In cell membranes, cholesterol acts as a buffer and is found between phospholipids. At high temperatures, the cholesterol molecues maintain rigidty by restricting phospholipid movement. At low temperatures, cholesterol prevents tight packing of phospholipids and therefore maintaines fluidity.
Campbell, N & Reece, J. (2005). Basic Principals of Animal Form and Function. Biology
(7th ed). pp(820-843). San Fransisco, CA. Pearson.
Campbell, N & Reece, J. (2005). Membrane Structure and Function. Biology (7th ed).
pp(820-843). San Fransisco, CA. Pearson.