Why do cells need to be able to transport things across their membranes

Cell membranes are selectively permeable which means it allow certain molecules to move across it into and out of the cell. Cells need to be able to transport these substances to live and grow.

Transport of ions, water maintains the osmotic pressure of the cell. Transport of sugars like glucose is necessary to generate energy for the metabolic activities of the cell. Gases like CO2 are waste products of metabolic reaction which are removed by the cell through the cell membrane. Amino acids are required to make proteins.  

Transport across cell can occur through active and passive transport and transport of these substance are necessary for a cell to live and function properly.

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