Test on Biomembrane Structure, Function, and Transport

Question 1: All polar molecules can cross lipid bilayers passively without assistance, provided a concentration gradient exists.

A. Ano

B. Ne

Explanation: Only small uncharged polar molecules can cross passively. The study materials specify that large polar molecules do not cross passively under these conditions.

Question 2: Functional asymmetry of a lipid bilayer indicates that the two leaflets of the membrane have identical lipid compositions and associated proteins.

A. Ano

B. Ne

Explanation: Functional asymmetry means that the two leaflets of the bilayer have different lipid compositions and different associated proteins, allowing the "inside" and "outside" of the membrane to perform different tasks.

Question 3: Based on the provided materials, which statement accurately describes the role of cholesterol in maintaining membrane fluidity?

A. Cholesterol primarily increases membrane fluidity at all temperatures.

B. Cholesterol stabilizes the membrane at high temperatures.

C. Cholesterol prevents the membrane from freezing at low temperatures.

D. Cholesterol decreases membrane fluidity by increasing the saturation of fatty acid chains.

Explanation: The study materials state that 'Cholesterol acts as a bidirectional regulator of fluidity, stabilizing the membrane at high temperatures and preventing it from freezing at low temperatures.'

Question 4: Which statement accurately describes the characteristics of passive transport (diffusion) across lipid bilayers, according to the provided study materials?

A. It requires the movement of two molecules in opposite directions, creating an electrical potential.

B. It allows small non-polar molecules and small uncharged polar molecules to cross, provided a concentration gradient exists.

C. It is an electrogenic process that results in a net translocation of charge across the membrane.

D. It always involves the transport of a single molecule, such as glucose, against its concentration gradient.

Explanation: The study materials state that 'Small non-polar molecules (like O2) and small uncharged polar molecules can cross passively. The primary condition is the existence of a concentration gradient.' Options mentioning electrogenic processes, antiport, or movement against a concentration gradient describe active or specific facilitated transport mechanisms, not passive diffusion as defined for these molecules in the materials.

Question 5: Phosphatidylinositol participates in cell signaling.

A. Ano

B. Ne

Explanation: Phosphatidylinositol is identified as one of two glycerophospholipids that participate in cell signaling.