Diffusion, osmosis and active transport, the factors affecting them, and osmosis in plant and animal cells.
Diffusion
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration (down a concentration gradient), as a result of their random motion. It needs no energy from respiration. Examples: oxygen into cells, carbon dioxide out, gas exchange in the lungs and leaves.
Rate of diffusion increases with a steeper concentration gradient, higher temperature, shorter distance, and a larger surface area.
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