A rabbit fleeing a coyote and a duck's extended flight during migration both involve muscular activity with high demands for metabolic fuel. However, the source of fuel and the pathways for ATP production differ. A rabbit's short‑term need for ATP is supplied by the breakdown of stored glycogen and glycolysis under anaerobic conditions. ATP for a duck's extended flight is supplied by the breakdown of fats to acetyl-CoA, the citric acid cycle, and oxidative phosphorylation. The short‑term intense run and the long‑term flight require coordinated regulatory controls on the central metabolic pathways of glycolysis, citric acid cycle, and oxidative phosphorylation. Match the actions of metabolic regulators with the type of muscular activity.

Short-term, intense muscular activity:

1. Low [O2] inhibits the citric acid cycle: - In the low supply of oxygen the pyruvate does not enter into the citric acid cycle, hence is converted to lactic acid by the enzyme lactate dehydrogenase in presence of NADH2. NADH2 is produced in glycolysis pathway (G3P to 1, 3-bisPG) inhibits the continuation of glycolysis. Since glycolysis is the sole source of energy in absence of oxygen, so to continue the glycolysis pathway, NADH2 must be utilized.

2. High [ADP] stimulate PFK-1 activity: - PFK-1 converts F6P to F1,6 bisP, which is the most regulatory enzyme in the glycolysis pathway. High concentration of ATP, citrate, H + (high energy state of the cell) inhibits the activity of PFK-1 means prevents the glycolysis pathway. The low energy level of the cell (AMP, Pi) activates the PFK-1 enzyme. Higher muscular activity depletes ATP rapidly, production of ADP increases. Now ADP is being converted to AMP and Pi, in turn, activates the PFK-1.

Long Term, continuous muscular activity:

3. High [ATP] inhibits PFK-1: - Flying migratory birds adopt such metabolism during their migratory period so that they can utilize their stored fat as the energy source because only glycolysis pathway during continuous muscular activity will lead to the accumulation of lactate which is very harmful to the muscles. So the fatty acid metabolism leads to the production of Acetyl CoA that in turn enters in the citric acid cycle and provide more energy.

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Explanation:

Short-term, intense muscular activity:

1. Low [O2] inhibits the citric acid cycle: - In the low supply of oxygen the pyruvate does not enter into the citric acid cycle, hence is converted to lactic acid by the enzyme lactate dehydrogenase in presence of NADH2. NADH2 is produced in glycolysis pathway (G3P to 1, 3-bisPG) inhibits the continuation of glycolysis. Since glycolysis is the sole source of energy in absence of oxygen, so to continue the glycolysis pathway, NADH2 must be utilized.

2. High [ADP] stimulate PFK-1 activity: - PFK-1 converts F6P to F1,6 bisP, which is the most regulatory enzyme in the glycolysis pathway. High concentration of ATP, citrate, H + (high energy state of the cell) inhibits the activity of PFK-1 means prevents the glycolysis pathway. The low energy level of the cell (AMP, Pi) activates the PFK-1 enzyme. Higher muscular activity depletes ATP rapidly, production of ADP increases. Now ADP is being converted to AMP and Pi, in turn, activates the PFK-1.

Long Term, continuous muscular activity:

3. High [ATP] inhibits PFK-1: - Flying migratory birds adopt such metabolism during their migratory period so that they can utilize their stored fat as the energy source because only glycolysis pathway during continuous muscular activity will lead to the accumulation of lactate which is very harmful to the muscles. So the fatty acid metabolism leads to the production of Acetyl CoA that in turn enters in the citric acid cycle and provide more energy.