SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Cell response mechanisms. Illustration showing the ways that a cell (round, upper centre) can respond to stimuli or signals from both the external environment (top) and from other cells (blue, lower right). Both types of responses are mediated through proteins embedded in the cell membrane (shown here as a phospholipid bilayer, light blue) and inside the cell. These proteins are called receptors (examples shown are yellow, red and orange). Signals from other cells are chemical in nature. Signals from the external environment can be chemical or physical. For this artwork with labels, see C023/8837.
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