The hemoglobin in mammalian blood is usually thought of simply as increasing the amount of O2 that can be carried by each litter of blood. Explain how the presence of hemoglobin in the blood also makes possible the rapid uptake of O2 by the blood as it flows through the lungs.

The hemoglobin in mammalian blood is usually thought of simply as increasing the amount of O2 that can be carried by each litter of blood. Explain how the presence of hemoglobin in the blood also makes possible the rapid uptake of O2 by the blood as it flows through the lungs.