Final answer:
Active transport enables organisms to regulate the uptake of molecules and ions against their concentration gradients using energy, often via transporter proteins and ion pumps. The correct option is b) Active transport
Step-by-step explanation:
Organisms must constantly regulate the uptake of certain molecules and ions and the exclusion of others. This is achieved through several mechanisms, one of which is active transport.
Active transport is the movement of a substance across a cell membrane against its concentration gradient, from an area of lower concentration to higher concentration, using energy usually in the form of ATP.
This process often involves transporter proteins and ion pumps that are fundamental for maintaining concentration gradients of ions across cell membranes.
Other mechanisms of molecule and ion transport across cell membranes include passive diffusion, facilitated diffusion, co-transport (or secondary active transport), and endocytosis.
While passive diffusion and facilitated diffusion move substances down their concentration gradients without using cellular energy, active transport requires energy to move substances against the gradient.
Finally, endocytosis involves the engulfing and internalization of substances by the cell membrane, which also requires energy. The correct option is b) Active transport