How do the small molecules of oxygen and carbon dioxide move through the cell membrane? A.
passive transport by diffusion
B.
active transport by endocytosis
C.
active transport by carrier proteins
D.
passive transport by osmosis

A.  passive transport by diffusion

Explanation:

Diffusion and osmosis are both types of passive transport. They do not require energy. Diffusion is the general term for the process. Osmosis is the diffusion of water molecules.

Many small, uncharged molecules can cross the cell membrane by diffusion. Oxygen and carbon dioxide are examples of two small molecules that pass the cell membrane by passive transport.

Larger or charged molecules require energy to cross the cell membrane. This is achieved by active transport.