ISSA Nutritionist Practice Exam

A thin polar membrane made of pairs of lipid molecules is known as a(n)?

1. Lipid bilayer

2. Cell wall

3. Plasma membrane

4. Proteins

The correct answer is: Lipid bilayer

A thin polar membrane made of pairs of lipid molecules is known as a lipid bilayer. The lipid bilayer is fundamental to the structure of cell membranes, composed primarily of phospholipids that arrange themselves into two layers. Each phospholipid molecule has a hydrophilic (water-attracting) "head" and two hydrophobic (water-repelling) "tails." This arrangement results in a membrane that is selectively permeable, allowing certain substances to pass while blocking others. The bilayer forms the basic structure of biological membranes, such as the plasma membrane, which encases the cell and maintains its integrity by separating the internal environment of the cell from the external surroundings. The characteristics of the lipid bilayer are crucial for the functionality of cellular processes, including signaling, transport, and communication between cells. While the plasma membrane is an example of a lipid bilayer, it is more specific and refers to the outer boundary of a cell. The term “cell wall” typically applies to rigid structures found in plants and bacteria, which are not characterized as lipid bilayers. Similarly, proteins are distinct molecules that can be embedded in or attached to the lipid bilayer but do not describe the membrane structure itself. Thus, lipid bilayer is