In most mammals, it involves oxygen from air being trasported across the "type I pneumocyte" (a broad, thin, leaf-like cell) which makes up the lining of the alveoli (air sacs) of the lungs. The other cell in close association with the pneumocyte is the 'endothelial cell'. This cell makes up the lining of the small blood vessel next to alveoli. Gas is exchanged across these cells by diffusion.

Carbon dioxide, the main waste product of metabolism, diffuses rapidly across these two cells so we can exhale it.

Oxygen is not as soluble and the hemoglobin of blood facilites this diffusion so we can absorb it into our blood.

Pneumocyte. There are two types: Type I cells make up the lining of the air sacks (alveoli) in the lung, type II cells produce a slick liquid called surfactant that helps coat the alveoli and keep them from collapsing when we exhale.

• Red Blood Cells
• Egg Cells
• Nerve cells
• Leaf cells (Palisade)
• Root hair cell
• Skin cells
• Cheek cells
• Sperm cells
• Brain cells

The different types of cell transport are the active transport and the passive transport. The active transport is energetic and fast while the passive transport is slow and soothing. The answer could be Osmosis and Diffusion. The only difference between osmosis and diffusin is that osmosis involves water molecules.