SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Membrane permeability. Illustration showing the relative permeability of a phospholipid bilayer (cell membrane) to different molecules and ions. Permeability is high for small, uncharged molecules such as carbon dioxide (CO2), nitrogen (N2), oxygen (O2) and ethanol. Permeability is moderate for water and urea. Permeability is low for polar organic molecules like glucose. Permeability is very low for ions and large macromolecules like sodium, potassium, magnesium, calcium, chloride, hydrogen carbonate, and dihydrogen phosphate ions, and amino acids, proteins, polysaccharides and nucleic acids (DNA and RNA). For this artwork without labels, see image C023/8770.
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