Does diffusion require energy?
When molecules go against biological membrane there are two ways active and passive transport. Active transport of molecules requires energy for transport.
Passive transport of molecules do not require energy.
Diffusion is transport of respiratory gases. It works as per concentration of gases. It is the partial pressure of gases. For example in air oxygen is 20%. In blood oxygen is 15%. The partial pressure of oxygen in air is more in air and less in blood. Oxygen therefore moves in blood by diffusion.