S-Cool Revision Summary

S-Cool Revision Summary

"Respiration is the chemical process of releasing energy from organic compounds."

Gas exchange: The movement of oxygen into an organism and carbon dioxide out of an organism.

Breathing: The ventilation movements that are needed in some larger animals so that efficient gas exchange can take place. It involves ribs, intercostal muscles, the diaphragm and lungs.

Respiration: The process by which complex organic molecules are broken down to release energy.

Aerobic respiration: Requires oxygen to fully oxidise the organic molecule. This releases lots of energy.

Anaerobic respiration: The breakdown of the molecule without oxygen. This releases much less energy.


ATP (adenosine triphosphate) is the universal currency of energy. It is a small molecule with 3 phosphate groups (P) attached to an adenosine molecule i.e. Adenosine-P-P-P

Many of the reactions in the stages of respiration involve oxidation by the removal of electrons or hydrogen atoms (H). These are transferred to electron/hydrogen carriers. Ultimately they are passed to oxygen to form water right at the very last stage of respiration.

Two important electron/hydrogen carriers are NAD (nicotinamide adenine dinucleotide), and FAD (flavin adenine dinucleotide).

Oxidation is the addition of oxygen, the removal of hydrogen or the loss of electrons.

Reduction is the addition of hydrogen, the removal of oxygen or the gain of electrons.

A quick way to remember this is "OILRIG":

O xidation I s L oss, R eduction I s G ain.

This is also known as the citric acid cycle or the tricarboxylic acid cycle.

For each glucose molecule, there were 2 pyruvic acid molecules formed, (and therefore 2 acetylCoA molecules formed) so the whole cycle takes place twice for every glucose molecule respired.

Production of ATP using NADH and FADH

So far we have in total, from one glucose molecule...


4 ATPs made directly

10 reduced NADs

2 reduced FADs

Now all the hydrogen from the reduced hydrogen carriers enters a chain of reactions, which ultimately yields energy in the form of ATP.

This theory about how the ATP is actually made is called the chemiosmotic theory. Oxygen acts as the final electron acceptor in the chain, so the oxygen, electrons and hydrogen ions together form water.