Which of the following cannot pass through the membrane without the help of a membrane protein? a. carbon dioxide; b. water; c. oxygen; d. charged molecules

Verified step by step guidance

1. Identify the properties of each molecule listed in relation to membrane permeability. Molecules that are nonpolar and small, such as carbon dioxide and oxygen, can diffuse through the lipid bilayer of the cell membrane without assistance.
2. Consider the polarity and size of water. Although water is a polar molecule, it is small enough to pass through the membrane via osmosis, but it often uses specialized channels called aquaporins to move more efficiently.
3. Analyze the nature of charged molecules. Charged molecules, due to their electrical charge, cannot easily cross the hydrophobic core of the lipid bilayer without assistance.
4. Compare the characteristics of the molecules listed with the general rules of membrane permeability. Nonpolar molecules and small uncharged polar molecules can diffuse through the membrane, but ions and large polar molecules generally require assistance.
5. Conclude which molecule among the options provided requires a membrane protein to facilitate its passage through the membrane. In this case, charged molecules need help from transport proteins like ion channels or carriers.