Question

3) Movement of substances within and between body fluids,

sometimes across a barrier such as the cell membrane is essential
to normal physiology. Mention the direction, requirement and one
example of

Answer 1

Active transport is a vital physiological process where living membranes expend energy to move substances against a concentration gradient, as exemplified by cypress tree roots extracting water from salt water and kidney functions.

Step-by-step explanation:

The movement of substances within and between body fluids across barriers such as the cell membrane is fundamental to physiology. One example of this is active transport, where substances move in a direction opposite to what would occur via diffusion. For instance, cypress tree roots can extract pure water from salt water, an action requiring energy as it goes against the osmotic gradient.

This contrasts with passive transport, such as osmosis or diffusion, which relies on a concentration gradient. Active transport is crucial for processes like the function of kidney cells, where it is employed to regulate the movement of substances into and out of the blood. This process requires ATP and is significant, with estimates suggesting that as much as 25% of the body's energy is dedicated to it.