Movement of Minerals across Root Hair Cells by Active Transport.

Up take of  minerals by the root hair cell is very important for a plant's growth.  However, it does not always uses diffusion.  Plant root hair cells are specialised cells.  They grow into long thin 'hair', giving the plant a large surface to absorb minerals and water.   

When the concentration of minerals is higher in the root hair cell than the  surrounding soil, it is unable to absorb these using diffusion.  The plant instead uses a method called ACTIVE TRANSPORT for absorption.  This uptake of minerals is against the concentration gradient and the plant has to spend energy to do this.  The energy used come from respiration.

Active transport also happens in animals.  For example, in humans the uptake of glucose from the gut and from the kidney tubules. See below!

Animation of root hair cell absorbing minerals.

After a large meal, your gut has lots (high concentration) of amino acids, fatty acids, glycerol and glucose.  These get absorbed into the blood stream by simple diffusion.  However, when there are less (low concentration) nutrients in the gut then in the blood and your body needs them, these are then absorbed by active transport.

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Osmosis