Title: Optional

Text: Passive transport moves material down its concentration gradient. It requires no energy input and stops once equilibrium is reached. However, some cells require a concentration gradient to be created and maintained. Other cells must take in or expel materials too large to fit through a membrane protein. When passive transport will not get the job done, cells resort to active transport, which requires energy in the form of ATP (adenosine triphosphate). Jeder Absatz wird ein Test sein.

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