Question

a cell membrane is composed of a double layer of lipids in which many kinds of proteins are embedded. many of these proteins act like gates, allowing only certain particles to enter or leave the cell. when a particle has to go against its concentration gradient through one of these gates, energy is supplied by the cell to the correct protein to move the particle through the membrane. a sodium - potassium ion pump is an example of a type of carrier protein that uses a large portion of the cells energy to move sodium ions through the cell membrane.
what is a primary function of a cell membrane?
a. determining genetic traits
b. defending against foreign particles
c. breaking down proteins for energy
d. generating energy from mineral nutrients

Explanation:

The cell membrane has proteins acting as gates (like the sodium - potassium pump) that control particle movement. This is a form of defense against unwanted foreign particles (by regulating what enters and leaves). Genetic traits are determined by DNA (not the cell membrane). Breaking down proteins for energy is mainly done by processes like cellular respiration in organelles (not the membrane's primary role). Generating energy from mineral nutrients is not a main function of the cell membrane.

Answer:

B. Defending against foreign particles