Movement of molecules

​Diffusion is the movement of molecules from a high concentration to a low concentration gradient. ​Examples of diffusion in everyday life includes :

• ​Smell of perfume diffuses through the air.

• ​CO₂ diffuses out of blood into lungs.

• ​O₂ diffuses into blood from lungs.

• ​CO₂ diffuses into leaf of a plant and O₂ diffuses out of the leaf during photosynthesis.

​Osmosis is a form of diffusion. Osmosis is the movement of water molecules down a concentration gradient, through a partially permeable membrane. Therefore, for osmosis, you need :

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• ​A concentration gradient

• ​A partially permeable membrane.

• ​Water molecules

​Active transport is the movement of molecules against a concentration gradient through a partially permeable membrane using energy from respiration. Examples of active transport are :

• ​ Uptake of glucose in the small intestine

• ​Uptake of ions by root hair cells.