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Explain why biological membranes are said to be selectively permeable or semipermeable. Address how materials like...

Explain why biological membranes are said to be selectively permeable or semipermeable. Address how materials like amino acids, carbohydrates, ions and water can pass through the biological membrane. Be sure to talk about the similarities and differences between diffusion, facilitated diffusion, osmosis and active transport. (7 points)

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Expert Solution

Plasma membrane is semipermeable or selectively permeable. cell membrane is composed of lipid bilayer in which protein channels and receptors are embedded. Small molecules like water diffuse through this membrane from higher water concentration to lower water concentration. This is actually osmosis where cell membrane acts as semi permeable membrane. There are also aquaporins which are integral membrane proteins that serve as channels . some small molecules also pass through these pores. There are specific ion channels in the membrane which allows specific ions to pass through the membrane. Small uncharged molecules diffuse through plasma membrane by diffusion, but when size increases such as glucose or amino acids, they need specific transmembrane receptor to be transported. In Active transport, the energy for transportation is derived from hydrolysis of ATP molecules. Facilitated diffusion is also an passive process in which energy is not needed. It is also occurs spontaneously from higher to lower concentration. So, diffusion, osmosis and passive diffusion does not require energy from ATP hydrolysis but active transporter needs energy from ATP. Through facilitated diffusion large polar molecules are transported which are hydrophilic in nature.


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