How do survive animals on mountain?

At high altitude, organisms are in a lower oxygen environment. This means their hemoglobin (and therefore blood) is less oxygenated and less oxygen is reaching vital organs and tissues. As a result, metabolic rate (which is dependent on oxygen) decreases. Cellular respiration is inhibited and ATP (energy) production is limited. Thus, fermentation rates increase in order to oxidize NADH (to NAD+) to continue glycolysis (glucose catabolism). Fermentation increases amounts of lactic acid which lower the pH of the cells, which further hinders oxygen's ability to bind to hemoglobin (the Bohr shift).

To compensate for these inconveniences, animals at high altitude often have a higher p50: they require less oxygen pressure to load oxygen on to hemoglobin and oxygenate their blood. By doing this, they increase their affinity for oxygen to bind. However, this is a long-term adaptation. Short-term adaptations include increasing blood flow, producing more red blood cells, and decreasing blood pH (in order to counteract hyperventilation: breathing deeply to get more oxygen, but detrimentally making blood more basic as a result).