Which homeostatic process moves particles against a concentration gradient?

• A. Passive diffusion
• B. Facilitated diffusion
• C. Active transport
• D. Osmosis

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of homeostasis, which refers to the maintenance of stable internal conditions in an organism despite changes in the external environment.
2. Step 2: Recognize that moving particles against a concentration gradient means transporting them from an area of lower concentration to an area of higher concentration, which requires energy input.
3. Step 3: Review the definitions of the processes listed: Passive diffusion and facilitated diffusion both involve movement of particles down their concentration gradient (from high to low concentration) and do not require energy. Osmosis specifically refers to the movement of water molecules across a semi-permeable membrane.
4. Step 4: Learn that active transport is the process that moves particles against their concentration gradient (from low to high concentration) and requires energy, typically in the form of ATP.
5. Step 5: Conclude that the correct answer is active transport, as it is the only process listed that fulfills the requirement of moving particles against a concentration gradient.