Given a partial pressure of oxygen in the tissues of 20 torr, calculate the percentage of oxygen released by hemoglobin and myoglobin, and assess their effectiveness as oxygen transporters.

• A. Both hemoglobin and myoglobin release 4% of their oxygen, making them equally ineffective.
• B. Hemoglobin releases 4% of its oxygen, while myoglobin releases 66%, making myoglobin more effective.
• C. Hemoglobin releases 66% of its oxygen, while myoglobin releases only 4%, making hemoglobin more effective.
• D. Both hemoglobin and myoglobin release 66% of their oxygen, making them equally effective.

Answer: (C)