Question

what part of a cell membrane is usually in contact with the interstitial fluid?
○ fatty acid tails
○ cholesterol
○ phosphate heads of phospholipids
○ hydrophobic molecules

Explanation:

The cell membrane is mainly composed of phospholipids, which have a hydrophilic (water - attracting) phosphate head and a hydrophobic (water - repelling) fatty acid tail. Interstitial fluid is an aqueous (water - based) environment. Hydrophilic substances interact with water - based environments. Fatty acid tails and hydrophobic molecules are water - repelling, so they are not in contact with the aqueous interstitial fluid. Cholesterol is mainly for membrane fluidity regulation. The phosphate heads of phospholipids are hydrophilic, so they are in contact with the interstitial fluid.

Answer:

C. phosphate heads of phospholipids