Positively charged molecules are often more easily endocytosed by cells than negatively charged molecules. Which of these BEST explains this observation? A. The hydrocarbon tails of membrane lipids are hydrophilic. B. The hydrocarbon tails of membrane lipids are hydrophobic. C. The phosphate group of membrane lipids are positively charged. D. The phosphate group of membrane lipids are negatively charged.

Answer is D. The phosphate group of membrane lipids are negatively charged.

The cell or plasma membrane is a bilayer of phospholipids. The two phospholipids layers are opposite to each other. Each phospholipid molecule consists of a phosphate group and a lipid. The phosphate form inner and outer layers of hydorphilic and are negatively charged 'heads' and lipid forms the tail, hydrophobic and non-polar. Since phosphate is negatively charged it repels negatively charged molecules and do allow them to pass through it.