The purpose of the
Krebs cycle is to generate
nadh in order to power the
electron transport chain. Up until this point,
respiration has produced relatively small amounts of
ATP. Now we finally get the big payoff.
Hydrogen ions from NADH are transferred across from the interior of the
mitochondria to the
external matrix, generating a
potential difference across the
internal membrane. Why is this good? Potential difference means
electrical current. We get a flow of
electrons across the internal membrane which are used to power
ATP synthase. Eventually the electrons become reunited with hydrogen ions and we use
oxygen as an acceptor (the reason for the requirement of oxygen in aerobic respiration) which produces water which is nice and easy to deal with.
The increased ability to produce energy that mitochondria provide is probably one of the reasons for us eukaryotes being up here and prokaryotes never getting round to discovering fire, inventing the wheel, forming civilisation, that sort of thing.