Answer to Question 1
The three main types of passive transport mechanisms, those that don't require energy, are simple diffusion, facilitated diffusion, and osmosis. Simple diffusion enables substances to cross cell membranes from a region of higher concentration to a region of lower concentration. Facilitated diffusion also involves the passive movement of a substance down its concentration gradient (high concentration to low concentration) but differs from simple diffusion in that it requires the assistance of a membrane-bound transport protein that escorts materials across cell membranes. However, for the body to function properly, some substances must cross cell membranes against the prevailing concentration gradient, moving from a region of lower concentration to that of a higher concentration. In cells, this uphill journey is accomplished by active transport mechanisms, which require the expenditure of energy as ATP.
Answer to Question 2
a
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