Organic compounds are made from: a. oxygen, carbon, and hydrogen b. carbon and hydrogen c. carbon and oxygen d. carbon only

The answer would be A. Remember your organic compounds are carbohydrates, proteins, lipids and nucleic acids. All of these contain oxygen, carbon and hydrogen.

Carbohydrates- carbon, hydrogen, oxygen

Lipids- carbon, hydrogen, oxygen

Proteins- carbon, hydrogen, oxygen, nitrogen

Nucleic acids- carbon, hydrogen, oxygen, nitrogen, phosphorus

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.