Which of the following structures separates the right and left pleurae?

a. Pathogen: A pathogen is a disease-causing organism like bacteria, virus, or parasite. It can trigger an immune response, but not necessarily a hypersensitivity reaction.

b. Allergen: An allergen is a foreign substance (like pollen, dust mites, or food) that can trigger an immune response in an already sensitized individual. This response can lead to allergy symptoms like hay fever or anaphylaxis

c. Immunogen: An immunogen is any substance that can trigger an immune response, but not necessarily a hypersensitivity reaction. It can be a pathogen, allergen, or other foreign substance.

d. Fibrinogen: Fibrinogen is a blood protein involved in blood clotting, not allergic reactions.

a. The plasma membrane is composed of a bilayer of protein molecules: This is incorrect. The plasma membrane is primarily composed of a bilayer of phospholipids, with proteins interspersed within this bilayer.

b. The plasma membrane is selectively permeable: This is correct. The plasma membrane regulates the entry and exit of substances, allowing certain molecules to pass while restricting others.

c. The plasma membrane does not participate in cellular activities: This is incorrect. The plasma membrane is actively involved in various cellular activities, including signaling, transport, and maintaining homeostasis.

d. The plasma membrane receptors are specialized lipids: This is incorrect. Receptors on the plasma membrane are typically proteins, not lipids, which are involved in signal transduction and cellular communication.