Which of the following statements best describes a characteristic of biological membranes?

• A. They are impermeable to all ions and small molecules.
• B. They consist solely of proteins and carbohydrates.
• C. They are composed of a phospholipid bilayer with embedded proteins.
• D. They are rigid structures that do not allow any movement of molecules.

Answer: (C)

Verified step by step guidance

1. Understand the structure of biological membranes: Biological membranes are primarily composed of a phospholipid bilayer. This bilayer forms the fundamental structure of the membrane, providing a semi-permeable barrier between the cell and its environment.
2. Recognize the role of embedded proteins: Proteins are embedded within the phospholipid bilayer and serve various functions, including transport, signaling, and structural support. These proteins can be integral (spanning the membrane) or peripheral (attached to the surface).
3. Consider the permeability of membranes: Biological membranes are selectively permeable, meaning they allow certain ions and small molecules to pass through while restricting others. This selective permeability is crucial for maintaining homeostasis within the cell.
4. Evaluate the flexibility of membranes: Biological membranes are not rigid structures; they are fluid and dynamic. The fluid mosaic model describes this characteristic, indicating that lipids and proteins can move laterally within the layer, allowing for flexibility and adaptability.
5. Identify the correct statement: Based on the understanding of biological membranes, the statement 'They are composed of a phospholipid bilayer with embedded proteins' accurately describes a characteristic of biological membranes.