Exercise 10. Fill in prepositions from the box below where necessary

1. _____ humans the compound used to transport oxygen is known ______- hemoglobin.

2. Hemoglobin is an iron-containing protein ______ red blood cells that is responsible ______ transporting oxygen ______ the tissues and removing carbon dioxide ______ them.

3. _____ the lungs, hemoglobin, known for its deep red color, reacts _____ oxygen to form oxyhemoglobin.

4. Oxyhemoglobin travels _______ the bloodstream to cells, where it breaks down to form hemoglobin and oxygen, and the oxygen then passes into cells.

5. On the way back, hemoglobin combines _____ carbon dioxide to form carbaminohemoglobin, an unstable compound that, once again, breaks down and releases _______ the surrounding environment.

Exercise 12. Fill in the gaps with the words and word-combinations from the box:

Mechanism of respiration

Under normal conditions, humans cannot ______ much oxygen in the body. Apnea of more than ____________________ leads to severe lack of oxygen in the blood circulation. Permanent brain damage can occur after _________________ and death will ensue after a few more minutes unless ventilation is restored.

Untrained humans cannot sustain voluntary apnea for more than one or two minutes. The reason for this is that the rate of breathing and the volume of each breath are tightly regulated to maintain constant values of CO2 tension and pH of the blood. In apnea, ________ is not removed through the lungs and accumulates in the blood.

When a person is immersed in water, physiological changes due to the mammalian diving reflex enable somewhat _______________ of apnea even in untrained persons. Tolerance can be trained. World-class divers can hold their breath underwater up to depths of _______________ and for more than _______________. Apneists, in this context, are people who can hold their breath for a long time.