Which of the following contain both hydrophilic and hydrophobic properties and are often found in cell plasma membranes? (A) Nucleotides (B) Phospholipids (C) Water (D) Amino acids

Hydrophilic molecules are those that form bonds with water or dissolve easily in water, whereas hydrophobic molecules do not interact or dissolve in water. In the context of cell plasma membranes, these properties play a crucial role in their structure and function.

The plasma membrane is a selective barrier that separates the cell's contents from its surrounding environment, regulating what enters and exits the cell. It is composed of a lipid bilayer primarily containing phospholipids, as well as embedded proteins, carbohydrates, and other molecules.

(A) Nucleotides: Nucleotides are the building blocks of nucleic acids, like DNA and RNA. They do not possess both hydrophilic and hydrophobic properties and are not a major component of cell plasma membranes. (B) Phospholipids: Phospholipids are a type of lipid that has a hydrophilic (water-loving) phosphate head and hydrophobic (water-fearing) fatty acid tail. They self-assemble into a bilayer in the cell plasma membrane, with the hydrophilic heads facing the watery interior and exterior of the cell and the hydrophobic tails facing each other. (C) Water: Water is a polar molecule, and as such, it is hydrophilic. It does not have hydrophobic properties. (D) Amino acids: Amino acids are the building blocks of proteins. While some amino acids have hydrophilic side chains, others have hydrophobic side chains. However, amino acids themselves are not found in the cell plasma membrane as they are constituents of proteins, which are embedded within the membrane.

After evaluating the properties of each option, it becomes clear that option (B) Phospholipids possess both hydrophilic and hydrophobic properties and are a major component in cell plasma membranes.