<span>The body needs oxygen for cellular respiration. When doing strenuous activity, such as lifting weights, the mitochondria cannot get enough oxygen. Without oxygen to act as an electron receptor, the body creates lactic acid to "reset" coenzymes to continue respiration.</span>
The answer for the year of 2017 would be more than 90 million. Hope this helps.
That would be cellular respiration.
An autotroph is an organism that prepares its own food using simple organic materials whist a heterotroph is an organism that cannot prepare its own food but depends on other organisms for survival.
