AP BIOLOGY

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

Detailed explanation-2: -What Do Membranes Do? Cell membranes serve as barriers and gatekeepers. They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly.

Detailed explanation-3: -Small uncharged molecules can diffuse freely through a phospholipid bilayer. However, the bilayer is impermeable to larger polar molecules (such as glucose and amino acids) and to ions.

Detailed explanation-4: -Answer and Explanation: Large molecules, polar molecules, and ions, cannot easily pass through the cell membrane. Large molecules, such as glucose, amino acids, and proteins, are simply too big to fit through the phospholipid bilayer.

Detailed explanation-5: -Not everything enters the cell through passive transport. Only the smallest molecules like water, carbon dioxide, and oxygen can freely diffuse across cell membranes. Larger molecules or charged molecules often require an input of energy to be transported into the cell.