Question

select the true statements. carbon dioxide only crosses the cell membrane in one direction. diffusion is a form of passive transport. carbon dioxide can move across cell membranes via simple diffusion because it is large and polar. the unassisted diffusion of molecules directly through the phospholipid bilayer is called simple diffusion.

Explanation:

• Diffusion is a form of passive transport: Passive transport does not require energy input. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, which fits the definition of passive transport.
• The unassisted diffusion of molecules directly through the phospholipid bilayer is called simple diffusion: Simple diffusion specifically refers to the process where small, non - polar molecules (like oxygen, carbon dioxide) move across the phospholipid bilayer without the help of transport proteins.

• Carbon dioxide only crosses the cell membrane in one direction: This is false. Carbon dioxide movement across the membrane depends on concentration gradients. For example, in cells, if the intracellular concentration of \(CO_2\) is higher than the extracellular concentration, \(CO_2\) will move out. But in other situations (e.g., in some aquatic plants under certain conditions), if the external \(CO_2\) concentration is higher, it can move in.
• Carbon dioxide can move across cell membranes via simple diffusion because it is large and polar: Carbon dioxide (\(CO_2\)) is a small, non - polar molecule. It is the small size and non - polar nature that allow it to pass through the non - polar interior of the phospholipid bilayer by simple diffusion.

Answer:

• B. Diffusion is a form of passive transport.
• D. The unassisted diffusion of molecules directly through the phospholipid bilayer is called simple diffusion.