The passing of a water down a concentration gradient (high to low), through a partially permeable membrane.
The passing of a liquid or gas down a concentration gradient.
The movement of a substance against the concentration gradient (low to high) using energy from respiration.
Tiny moist air sacs in the lungs with a large surface area and a rich blood supply which maintain a concentration gradient in both directions.
Carbon Dioxide + Water + Energy --> Glucose + Oxygen