Phospholipid Arrangement in Cell Membranes

Steps:

• In the fluid mosaic model, phospholipids form a bilayer with hydrophilic heads facing aqueous environments outward.
• Hydrophobic fatty acid tails cluster inward, away from water, to minimize energy.
• Evaluate statement 1: incorrect, as tails do not point outwards.
• Evaluate statements 2 and 4: both correct per bilayer structure; statement 3 incorrect, as polar heads primarily provide stability, not flexibility (which arises from tail saturation and cholesterol).

Why D is correct:

• D selects statements 2 and 4, aligning with the hydrophobic effect where nonpolar tails associate internally in the bilayer (defined by thermodynamics of water exclusion).

Why the others are wrong:

• A includes incorrect 1 and 3.
• B includes incorrect 1 and 3.
• C includes unmentioned 4 but omits correct 2.

Final answer: D