Biochemists working with isolated mitochondria recognize five energy "states" of mitochondria, depending on the presence or absence of essential substrates for respiration-O2 , ADP, oxidizable substrates, and so forth. The characteristics of each state are:
State 1: mitochondria alone (in buffer containing Pi)
State 2: mitochondria + substrate, but respiration low due to lack of ADP
State 3: mitochondria + substrate + limited amount of ADP, allowing rapid respiration
State 4: mitochondria + substrate, but all ADP converted to ATP, so respiration slows
State 5: mitochondria + substrate + ADP, but all O2 used up (anoxia), so respiration stops (a) On the graph, identify the state that might predominate in each stage of the trace indicated with a letter.

(b) To determine whether isolated mitochondria exhibit respiratory control, one determines the ratio of rates of oxygen uptake in two different states. Which states?
(c) Which state probably predominates in vivo in skeletal muscle fatigued from a long and strenuous workout?
(d) Which state probably predominates in resting skeletal muscle of a well-nourished animal?
(e) Which state probably predominates in heart muscle most of the time?

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