Aresearcher makes two artificial membranes to study the effect of lipid components on fluidity properties of membranes. membrane (a) is made exclusively with a phospholipid that contains a long unsaturated hydrocarbon tail. membrane (b) is comprised exclusively of a phospholipid in which the hydrocarbon tail is short and unsaturated. at room temperature, membrane would be more fluid. at room temperature, water could pass through membrane more readily.

At room temperature, membrane B would be more fluid. At room temperature, water could pass through membrane membrane B  more readily.

Explanation:

The proportion of phospholipids with unsaturated tails regulates membrane fluidity and permeability. The phospholipid with unsaturated hydrocarbon tails does not pack tightly in the inner core of the membrane since the double bonds produce a kink. The membranes become more fluid and permeable with an increased proportion of phospholipids with unsaturated tails.

However, a membrane (A) made up of a phospholipid that contains a long unsaturated hydrocarbon tail is less fluid at room temperature than the membrane (B) containing phospholipid with a short unsaturated hydrocarbon tail due to more interactions between the long tails of the phospholipids. The increased interactions between the hydrocarbon tails of the phospholipids make the membrane more rigid and less fluid.

Among the given examples, membrane B will be more fluid and permeable due to less number of interaction and resultant loose packing of tails in the inner core as compared to membrane A.