Question

Which of the following is able to passively penetrate the plasma membrane (without a transport protein)?

1) Large polar molecules
2) O₂
3) Small charged particles
4) All of the choices are correct.

Answer 1

2)Oxygen (O₂) can passively penetrate the plasma membrane through simple diffusion, unlike large polar molecules and small charged particles that require transport proteins.

Step-by-step explanation:

Among the options given, O₂ (oxygen) can passively penetrate the plasma membrane without the need for a transport protein. Molecules like O₂ are nonpolar and small, therefore they can easily diffuse through the plasma membrane's lipid bilayer by simple diffusion. Polar substances and charged particles, such as large polar molecules and small charged ions, face challenges passing through the hydrophobic core of the plasma membrane. These substances typically require special transport proteins to move into or out of the cell.