Which of the following would be regarded as an organic molecule?

A. Maintaining boundaries: Maintaining boundaries refers to the separation between internal and external environments, such as the plasma membrane or skin, and is not directly related to removing carbon dioxide.

B. Excretion of metabolic waste: Expiration removes carbon dioxide, a byproduct of cellular respiration, from the body. This is a primary example of excreting metabolic waste to maintain proper internal chemical balance.

C. Responsiveness: Responsiveness is the ability of the body to detect and react to changes in the environment, such as moving away from a stimulus, which does not involve carbon dioxide removal.

D. Metabolism: Metabolism encompasses all chemical reactions in the body, including producing carbon dioxide as a byproduct. However, the act of exhaling carbon dioxide specifically exemplifies waste excretion, not metabolism itself.

A. Rubbing alcohol: Rubbing alcohol is a homogeneous solution of isopropyl alcohol and water. The molecules are evenly distributed, and no particles settle out over time. Because it does not separate, it is classified as a solution rather than a suspension.

B. Cytosol: Cytosol is the intracellular fluid that contains water, ions, and proteins in a dissolved or colloidal state. The particles remain dispersed and do not settle on standing. This makes cytosol more of a colloid or solution.

C. Blood: Blood is a suspension because it contains formed elements such as red blood cells, white blood cells, and platelets suspended in plasma. These components can separate out and settle if the sample is left undisturbed, fitting the definition of a suspension.

D. Salt water: Salt water is a solution formed when sodium and chloride ions completely dissolve in water. The ions remain evenly distributed and will not settle over time, which excludes it from being a suspension.