The correct answer is: A. The hydrophilic head groups of the lipid molecules are exposed to the outside of the cell and the cytoplasm, which is a water-like environment. The hydrophobic tails form an oily layer inside the membrane that keeps water out of the cell.
Plasma membrane of the cell is arranged in a bilayer of phospholipids. Phospholipids are amphipathic molecules which means that they have both hydrophilic and hydrophobic regions. The hydrophilic heads of phospholipids that are faced outward and hydrophobic layer located in the interior of the bilayer together make a good barrier between the interior and exterior of the cell, so the water and other polar or charged substances cannot easily cross the hydrophobic core of the membrane.
Answer:
A. The hydrophilic head groups of the lipid molecules are exposed to the outside of the cell and the cytoplasm, which is a water-like environment. The hydrophobic tails form an oily layer inside the membrane that keeps water out of the cell.
Explanation:
Cell membrane is composed of bilayer of phospholipid molecules. These molecules are amphipathic i.e. they have both polar and non polar components. The head is polar and composed of hydrophilic groups hence it faces the outside of the cell where there is polar environment created by the cytoplasm. The tails are composed of hydrophobic molecules so they are present inside the membrane and form an oily layer.
Small non polar molecules can cross the cell membrane easily because the interior of the membrane has non polar environment. Water moves slowly since its polar and sometimes it can not even cross the membrane directly and requires special proteins called as aquaporins. Hence, hydrophobic tails form an oily layer inside the membrane that keeps water out of the cell.
