we can not see, smell, or taste oxygen , yet without oxygen, none of us could survive longer than a few minutes.It is fortunate, then, that oxygen is the most common substance on earth.Oxygen is a gas ,mixed with other gases, it makes up about one -fifth of the air we breathe.Most of the oxygen in the word, though, does not float as a gas.Instead, the oxygen is bound up in combination whit other substances - in a solid or liquid form. This is because oxygen is chemically reactive, it readily combines with other substances, often giving off energy in the process, and burning is an example of oxygen at work .When a piece of timber burns, oxygen is combining with the wood and giving off heat. oxygen is also found in water, combined with atoms of another gas, hydrogen.Oxygen can be extracted from water by passing an electric current through it.The electricity breaks the water into its parts(the gases oxygen and hydrogen) and oxygen bubbles off.
Our bodies need oxygen to make the energy consumed when we use our muscle .The oxygen we breathe in is used to(burn) the food we eat, producing energy. This process is called respiration. Blood carries the oxygen from the lungs, which extract it form the air, to the muscles where it is needed to make energy.
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