Does active transport or passive transport of protons make the gradient? During ATP synthesis, is it active transport or passive transport ?

Answer 1

In a technical sense, you could consider it as active transport because even though no ATP is required for the H+ to be pumped across the membrane, there is an electrochemical energy that is required. This energy gradient is created when the electrons move down the ETC. This is referred to as secondary active transport.

The electrons from from NADH and FADH2 flow through the electron transport chain in the inner mitochondrial membrane generating a H+ buildup in the inner membrane space. This proton gradient (gradient of H+) flowing through the membrane enzyme complex ATP synthetase is the direct energy source for producing ATP. Again, in contrast to primary active transport, there is no direct coupling of ATP.