Which of the following accurately describes a physiological characteristic of the plasma membrane? a. it is made up of membrane lipids including phospholipids and cholesterol b. it is made up of membrane proteins like integral and peripheral proteins c. it separates intracellular fluid from extracellular fluid d. all the above e. none of the above
The correct answer and explanation is:
The correct answer is d. all the above.
Explanation:
The plasma membrane is a crucial structure that defines the boundary of a cell, controlling the movement of substances in and out, and maintaining the internal environment of the cell. Each of the options describes an important physiological characteristic of the plasma membrane:
a. It is made up of membrane lipids including phospholipids and cholesterol
The plasma membrane is primarily composed of a phospholipid bilayer, which forms its basic structure. Phospholipids have hydrophilic (water-attracting) heads facing the extracellular and intracellular fluids and hydrophobic (water-repelling) tails facing inward, creating a semi-permeable barrier. Cholesterol molecules are interspersed among the phospholipids, adding stability and fluidity to the membrane. Cholesterol prevents the membrane from becoming too rigid in cold temperatures and too fluid in warm temperatures, ensuring optimal function.
b. It is made up of membrane proteins like integral and peripheral proteins
Membrane proteins are embedded within or attached to the phospholipid bilayer and are essential for various functions. Integral proteins span the membrane and often serve as channels or transporters for molecules to cross the membrane. Peripheral proteins are attached to the membrane surface and are involved in signaling or maintaining the cell’s shape and structure. Together, these proteins help in communication, transport, enzymatic activity, and cell recognition.
c. It separates intracellular fluid from extracellular fluid
The plasma membrane acts as a selective barrier separating the intracellular fluid (cytoplasm) from the extracellular fluid. This separation is vital because the internal environment of the cell needs to be maintained differently from the external environment for the cell to function properly. The membrane controls which ions, nutrients, and waste products move in or out, maintaining homeostasis.
In summary, the plasma membrane’s physiological characteristics include its lipid composition (phospholipids and cholesterol), the presence of diverse proteins (integral and peripheral), and its fundamental role in separating intracellular and extracellular environments. All these features together define the structure and function of the plasma membrane, making option d the correct answer.