A Levels Biology (9700)•9700/13/M/J/18

Explanation
Amphipathic Nature of Phospholipids
Steps:
- Recall that phospholipids have a polar head and nonpolar tails.
- Understand that the polar head is hydrophilic, attracting water.
- Note that the nonpolar tails are hydrophobic, repelling water.
- Recognize that in water, these molecules arrange into a bilayer with heads facing water and tails inward.
Why C is correct:
- Phospholipids are amphipathic, with hydrophilic phosphate heads and hydrophobic fatty acid tails, driving spontaneous bilayer formation as defined by the hydrophobic effect in aqueous environments.
Why the others are wrong:
- A: Insolubility alone does not explain bilayer structure; it relates to overall amphipathicity.
- B: Solubility would disperse molecules, preventing organized bilayer formation.
- D: Fatty acid saturation affects fluidity but not the fundamental ability to form a bilayer.
Final answer: C
Topic: Fluid mosaic membranes
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