Question

You are exploring a rather inhospitable planet, which has seas that are somewhat hydrophobic in nature. Surprisingly, there are living organisms in the seas whose cytoplasm is hydrophobic to a similar degree. These organisms have membranes made primarily of phospholipids arranged in a bilayer. What is the most probable orientation of these phospholipids?

Answer 1

Answer: The polar heads of the phospholipids face toward the middle of the bilayer. And the hydrophobic fatty acid tails face outward.

Explanation:

The fact that the organisms have a hydrophobic cytoplasm indicates that it repels water. Plasma membranes surround the cytoplasm (part of the cell that surrounds the nucleus and is limited by the outer membrane) and these are composed of phospholipids which are a type of saponifiable lipids that make up the cell membranes, composed of an alcohol molecule (glycerol or sphingosine), to which two fatty acids (1,2-diazylglycerol) and a phosphate group are attached.  

The amphipatic character of the phospholipids allows them to self-associate through hydrophobic interactions between the long chain fatty acid portions of adjacent molecules. In our planet, the cytoplasm is composed of liquids, so the polar heads (which are hydrophilic, they attract water) project outwards towards the water where they can interact with the protein molecules. And the apolar tail (which are hydrophobic, it reels water) projects towards the interior of the lipid bilayer.

However in this inhospitable planet, as the cytoplasm is hydrophobic, the phospholipids will be oriented in the opposite direction. The polar heads of the phospholipids face toward the middle of the bilayer because they are hydrophilic and they can not be in touch with the cytoplasm. And the hydrophobic fatty acid tails face outward, because they are hydrophobic.