Which of the following molecules is most likely to passively diffuse across the plasma membrane?
* carbon dioxide
* glucose
* hemoglobin
* dna
* sodium ion

The plasma membrane is the biological membrane that separates the interior of the cell from its external environment. It is selectively permeable in nature and allows the transport of substances in and out of the cell either by passive transport or active transport.

Passive transport is the movement of substances from a region of their higher concentration to a region of their lower concentration through a semi-permeable membrane. Substances like carbon dioxide and oxygen move across the plasma membrane by diffusion which is a type of passive transport. It involves the diffusion of carbon dioxide down its concentration gradient. Carbon dioxide and oxygen are two molecules that undergo the process of simple diffusion across the plasma membrane.