<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 first one is second succession. The second question I don't understand.
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Answer:
A cell that results from the fusion of sperm and ovum is called a zygote. The process of fusion of sperm and ovum is called fertilization.
