This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Biochemistry
Neutral molecules are transpoed by 
Select and explain. 
A. Porin channels, B. Ionophores, C. Simple diffusion, D. None of the above
C: Simple diffusion
Answer: C: Simple diffusion 
Explanation: Simple diffusion occurs from higher to lower concentration. This does not require any energy. It is a very slow process.Diffusion of gases such as O2, CO2, NO and CO occurs at a rate that is solely dependent upon concentration gradients.Lipophilic molecules will also diffuse across membranes at a rate that is directly propoional to the solubility of the compound in the membrane.Ref: D M Vasudevan 7th edition Page no: 17