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<em>In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems</em>
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Kelp is eaten by sea otters. Kelp is a large, brown plant that grows in the sea and is used in some foods and medicines
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Human activities have a tremendous impact on the carbon cycle. Burning fossil fuels, changing land use, and using limestone to make concrete all transfer significant quantities of carbon into the atmosphere
