Answers

2015-10-10T12:20:34+05:30
1) when we walk uphill........there is a lot of effort made by us which requires a lot of energy and so.....we start breathing fast.

2) as we walk to a height above sea level...the oxygen level decreases.......so the rate of breathing increases because there is less amount of oxygen present.

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2015-10-10T21:11:54+05:30
There is less supply of oxygen, as it is required in highest amount

Oxygen, will nt be sufficient to reach to the muscles to provide us strength, if we force more it leads to accumulation of lactic acid, which causes muscle fatigue
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