AP BIOLOGY

Detailed explanation-1: -A membrane which allows certain substances to pass through it, but not others is called a selectively permeable membrane.

Detailed explanation-2: -The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot. Water can pass through between the lipids.

Detailed explanation-3: -Plasma membranes must allow certain substances to enter and leave a cell, while preventing harmful material from entering and essential material from leaving. In other words, plasma membranes are selectively permeable-they allow some substances through but not others.

Detailed explanation-4: -Examples of Selectively Permeable Membranes The most common example is the phospholipid bilayer cell membrane that surrounds every cell in our bodies. Another example of a selectively permeable membrane is the inner membranes of an egg. All cells in our body are surrounded by a phospholipid bilayer.

Detailed explanation-5: -Cell membranes are selectively permeable, so only certain substances can passively diffuse directly across the membrane. These substances include small, nonpolar molecules such as carbon dioxide and molecular oxygen.