In humans skin color widely varies. This is because skin color is?

Human skin color ranges in variety from the darkest brown to the lightest hues. An individual's skin pigmentation is the result of genetics, being the product of both of the individual's biological parents ' genetic makeup, and exposure to sun.

Explanation:

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the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.