Question

What are the molecules that are small and carry no charge and can pass directly through the phospholipid bilayer of the membrane without the assistance of any other molecules?

1) Proteins
2) Lipids
3) Carbohydrates
4) Water

Answer 1

Lipids are the small, nonpolar, uncharged molecules that can pass through the phospholipid bilayer without assistance, due to the hydrophobic nature of the membrane.

Step-by-step explanation:

The molecules that are small, carry no charge, and can pass directly through the phospholipid bilayer of the cell membrane are generally nonpolar molecules such as oxygen and carbon dioxide gases. Among the options provided, lipids are the molecules that can pass through the phospholipid bilayer without assistance. This is due to the hydrophobic nature of the fatty acid tails in the bilayer that allows other nonpolar molecules to diffuse through. Water is indeed a small molecule but it's polar, and although it can sometimes pass through the membrane by simple diffusion, it does not fit the criteria as well as lipids do.