If calcium levels within a man’s blood drop too low it can result in twitching, depression, coma, or even death. which characteristic of life is the man being affected by?

living things must maintain homeostasis.
living things are made of cells.
living things require energy.
living things reproduce.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

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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.