<P> 1 . Passive osmosis and diffusion : Some substances ( small molecules , ions ) such as carbon dioxide ( CO ) and oxygen ( O ) , can move across the plasma membrane by diffusion , which is a passive transport process . Because the membrane acts as a barrier for certain molecules and ions , they can occur in different concentrations on the two sides of the membrane . Diffusion occurs when small molecules and ions move freely from high concentration to low concentration in order to equilibrate the membrane . It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane . Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water . Osmosis , in biological systems involves a solvent , moving through a semipermeable membrane similarly to passive diffusion as the solvent still moves with the concentration gradient and requires no energy . While water is the most common solvent in cell , it can also be other liquids as well as supercritical liquids and gases . </P>
<P> 1 . Passive osmosis and diffusion : Some substances ( small molecules , ions ) such as carbon dioxide ( CO ) and oxygen ( O ) , can move across the plasma membrane by diffusion , which is a passive transport process . Because the membrane acts as a barrier for certain molecules and ions , they can occur in different concentrations on the two sides of the membrane . Diffusion occurs when small molecules and ions move freely from high concentration to low concentration in order to equilibrate the membrane . It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane . Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water . Osmosis , in biological systems involves a solvent , moving through a semipermeable membrane similarly to passive diffusion as the solvent still moves with the concentration gradient and requires no energy . While water is the most common solvent in cell , it can also be other liquids as well as supercritical liquids and gases . </P>
what is the role of the cell membrane in diffusion
what is the role of the cell membrane in diffusion
membrane acts as a barrier for certain molecules and ions
membrane acts as a barrier for certain molecules and ions