Define diffusion.

Define diffusion.

• A. The movement of particles from higher concentration to lower concentration, without energy input.
• B. The diffusion of water across a selectively permeable membrane from an area of higher water potential to lower.
• C. Movement of substances against a concentration gradient using energy.
• D. The splitting of water molecules to release energy.

Answer: (A)

Diffusion is the random movement of particles from an area of higher concentration to an area of lower concentration, and it happens without the input of energy. Molecules constantly collide and spread out, so they move down their concentration gradient until balance is reached. This passive spreading explains why gases and many small solutes move across cell membranes without using energy. The water-transport statement describes osmosis, a specific kind of diffusion for water across a semipermeable membrane driven by differences in water potential. The other options describe moving substances against a gradient using energy (active transport) or a chemical reaction that splits water, which aren’t diffusion.

Diffusion is the random movement of particles from an area of higher concentration to an area of lower concentration, and it happens without the input of energy. Molecules constantly collide and spread out, so they move down their concentration gradient until balance is reached. This passive spreading explains why gases and many small solutes move across cell membranes without using energy. The water-transport statement describes osmosis, a specific kind of diffusion for water across a semipermeable membrane driven by differences in water potential. The other options describe moving substances against a gradient using energy (active transport) or a chemical reaction that splits water, which aren’t diffusion.