Questions: Which of the following molecules can pass through the lipid bilayer without assistance? Select all that apply. sodium ion, a charged molecule water, a very small polar molecule oxygen, a small nonpolar molecule glucose, a large polar molecule

The molecules that can pass through the lipid bilayer without assistance are:

• Oxygen, a small nonpolar molecule

Explanation for each option:

1. Sodium ion, a charged molecule: Charged molecules, such as ions, cannot pass through the lipid bilayer without assistance because they are repelled by the nonpolar fatty acid tails of the phospholipids. Therefore, sodium ions cannot cross the lipid bilayer on their own.

2. Water, a very small polar molecule: Although water is a very small polar molecule, it can pass through the lipid bilayer, but it does so at a slow rate. However, it is not as efficient as nonpolar molecules. While water can pass through, it often requires assistance from specialized channels called aquaporins for more efficient transport.

3. Oxygen, a small nonpolar molecule: Small nonpolar molecules like oxygen can easily pass through the lipid bilayer without assistance because they are not repelled by the nonpolar fatty acid tails. Therefore, oxygen can cross the lipid bilayer on its own.

4. Glucose, a large polar molecule: Large polar molecules like glucose cannot pass through the lipid bilayer without assistance because they are too large to fit between the tightly packed phospholipids and are repelled by the nonpolar fatty acid tails. Glucose typically requires transport proteins to cross the membrane.

In summary, the molecule that can pass through the lipid bilayer without assistance is oxygen, a small nonpolar molecule.