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
Auxin transport.
The major muscles of the human body, anterior side.
Organisms can be classified according to their source of energy
fusion for energy
The battle plan of the body’s defenses.
Body plan of an aquatic snail and micrograph of a radula