electron transport chain

1. NADH 1. 5 e

2. NAD+ H+

3. FADH

4. FAD+ H+

5. O2 +4H+

6. H2O

7. ADP+ Pi

8. ATP

9. ATP synthase

10. the more H+ ions = charge and PH (H+ acidic) gradient

step 1 

NADH molecules bind to protein I and release their hydrogen atoms as protons (H+) and electrons (e-). FADH binds to complex II rather than complex I to release its hydrogen. The NAD and FAD molecules then return to the Krebs Cycle to collect more hydrogen, so these coenzymes are constantly shuttling between their oxidised and reduced forms

Step 2

The electrons are passed along the chain of proteins via a series of redox reactions . Each protein is at a slightly lower energy level than the previous one so energy is transferred at each stage. The energy of the electrons is used to pump protons across the inner mitochondrial membrane  in the intermembrane space by active transport through the proteins, forming a proton gradient across the membrane.

step 3

This process ensures that there is a proton gradient across the membrane. There is a charge and PH gradient as protons (H+) are positive and they are acidic 

Step 4 

The energy of the electrons is now stored in the form of the proton gradient across the inner mitochondrial membrane. It’s a bit like using energy to pump water uphill into a high reservoir, where it is stored as potential energy. And just as the potential energy in the water can be used to generate electricity in a hydroelectric power station, so the potential energy in the proton gradient can be used to generate ATP in the ATP synthase enzyme. The H+ diffuses across into the matrix as the inner membrane isn’t permeable to proton they diffuse they pass though stalked particles which contain ATP synthetase which uses the energy from the proton moving down the gradient to allow the condensation reaction between ADP +Pi to from ATP

Step 5

When the electrons reach the end of the transport chain they combine with hydrogen ions and oxygen to form water.

2H+ +2e + 1O

what is oxygen called in the electron transport chain 

The terminal electron acceptor 

What is the synthesis of ATP called and why

This synthesis of ATP is called oxidative phosphorylation because it uses oxygen to phosphorylate ADP. 

what is the method of storing energy across a proton gradient called

The method of storing energy by creating a proton gradient across a membrane is called chemiosmosis, and was discovered by Peter Mitchell in the 1960s

why is oxygen ( terminal electron acceptor) so key

process would stop

In the absence of oxygen there will be no terminal electron acceptor. Electrons will be unable to off load their electrons. The carriers will all become reduced and the flow of electrons will stop. This means there will be no energy to pump H+ to create the conc gradient. NADH will be unable to off load its hydrogen and e at the start of the ETC. The NAD will not be regenerated. without regenerated NAD the enzymes in the Krebs cycle will not work. This means were only generating ATP from glycolysis in aerobic respiration where a step is added to regenerate NADH to NAD