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The gas that is essential for human beings to breathe in for survival is?
A. Carbon dioxide
B. Oxygen
C. Nitrogen
D. Hydrogen
Correct Answer Is Option = Oxygen
Notes / Explanation
The gas that is essential for human beings to breathe in for survival is oxygen, which is one of the most important substances for the existence of almost all forms of life on Earth. The air that surrounds us is a mixture of several different gases, and although oxygen is not the most abundant gas in the atmosphere, it is the one that is most vital for the survival of human beings and most animals. When a person breathes in, the air enters the lungs, and from the lungs the oxygen passes into the blood, where it is carried by the red blood cells to every part of the body. The oxygen is then used by the cells of the body in a process that releases the energy stored in the food we eat. This energy is needed for every activity of the body, from moving and thinking to keeping the heart beating and maintaining body temperature, and without a continuous supply of oxygen the cells cannot produce this energy and cannot survive. This is why a person can live for some time without food or water but can survive for only a very few minutes without breathing. As the cells use oxygen to produce energy, they also produce a waste gas called carbon dioxide, which the blood carries back to the lungs so that it can be breathed out. In this way the process of breathing brings in the oxygen that the body needs and removes the carbon dioxide that it must get rid of. Oxygen is also essential for the process of burning, because nothing can burn without it, which is why removing the supply of oxygen is one of the ways of putting out a fire. A remarkable feature of nature is that the oxygen in the atmosphere is constantly being replaced by green plants, which take in carbon dioxide and release oxygen during the process by which they make their food in the presence of sunlight. This natural cycle ensures that the supply of oxygen in the air is maintained, linking the survival of animals to the existence of plants. For PPSC and other competitive examinations, the key points to remember are that oxygen is the gas that humans must breathe in to survive, that it is carried by the blood to the cells where it is used to release energy from food, that the body breathes out carbon dioxide as a waste product, and that green plants continually replenish the oxygen in the atmosphere.
