The interior of the phospholipid bilayers that make up all biological membranes is:
Composed of cholesterol
Composed of water
Composed of fats
Hydrophobic
Hydrophillic
The correct answer is that the interior of the phospholipid bilayers is hydrophobic.
To understand why, let's break it down:
1. Composed of cholesterol: Cholesterol is a lipid molecule found in cell membranes, but it is not the main component of the interior of phospholipid bilayers. While cholesterol does influence membrane fluidity and stability, it is not the defining factor of the interior composition.
2. Composed of water: Water is present in and around cellular membranes, but it does not make up the interior of the phospholipid bilayers. Water molecules are actually excluded from the hydrophobic interior due to the repulsion between water and the hydrophobic lipid tails.
3. Composed of fats: Phospholipids, not fats, are the main component of the phospholipid bilayers. Fats refer to triglycerides, which have glycerol and three fatty acids, and they are not the primary building blocks of cell membranes.
4. Hydrophobic: The interior of the phospholipid bilayers is indeed hydrophobic. Phospholipids consist of a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. When these phospholipids come together to form a bilayer, the hydrophobic tails cluster together in the interior, creating a hydrophobic environment that excludes water.
5. Hydrophilic: Hydrophilic molecules have an affinity for water. While the hydrophilic heads of the phospholipids are indeed present in the cell membrane, they mainly face the watery environments both inside and outside the cell. The hydrophilic heads do not make up the interior of the phospholipid bilayers.
So, to recap, the interior of the phospholipid bilayers is hydrophobic, meaning it repels water and allows for the formation of a stable and selectively permeable membrane in cells.