Question

In cold response, in order to keep the membrane in a fluid state, cells respond to changing conditions by ________?

1) altering the types of phospholipids of the membrane
2) desaturating single bonds in fatty acyl chains to form double bonds
3) reshuffling the chains between different phospholipid molecules to produce ones that contain two unsaturated fatty acids
4) changing membrane proteins
5) increasing the transition (melting) temperature of the lipid bilayer

Answer 1

Cells respond to cold by increasing the proportion of unsaturated fatty acids in their membranes to maintain fluidity, as unsaturated fatty acids prevent tight packing with their kinked structures.

Step-by-step explanation:

In cold response, cells maintain membrane fluidity by altering the types of phospholipids in the membrane. Particularly, cells increase the proportion of unsaturated fatty acids within the phospholipid bilayer. Unsaturated fatty acids have 'kinks' in their tails due to the presence of double bonds; these kinks prevent the fatty acid tails from packing tightly together and help maintain space between the phospholipid molecules, thus preserving membrane fluidity even in colder temperatures where membranes with saturated fatty acid tails would solidify. This adaptation is crucial for organisms like fish, which can change the fatty acid composition of their membrane lipids to remain functional in varying thermal environments.