Diffusion, osmosis and active transport, and enzymes as biological catalysts including the effects of temperature and pH.
Diffusion
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration (down a concentration gradient), due to their random motion. It needs no energy from respiration. Examples: oxygen entering cells, carbon dioxide leaving, gas exchange in the lungs and leaves.
The rate of diffusion increases with a steeper concentration gradient, higher temperature, shorter distance and larger surface area.
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