Low-head dams are dangerous structures that basically extend from one side of a riverbank to the other. Low-head dams block the water way partially and the water moving over the dam produces a strong circular current at the lower part of the dam. Low-head dams are dangerous to small boats and paddle craft because the strong circular current below the dam can trap small boats and paddle craft and pull them under the dam.
Answer:
Molecules which move against the concentration gradient across the cell membrane employ the mechanism of active transportation.
Explanation:
Normally, permitted molecules moves across the cell membrane of the cell by the process of diffusion and osmosis. This is used when molecules move from hypertonic region to hypotonic region (if ions) and hypotonic to hypertonic (if water). This is a passive transportation which do not require the expense of energy from the cell.
In contrast, when molecules move in or out of the cell against their concentration gradient, that is ions moving from hypotonic region to hypertonic region, they implore the expense of energy in form of adenosine triphosphate (ATP), and the involvement of the membrane carrier proteins. This is called active transport.
The answer is culinary. Hope this helps.
