In chemistry, give examples of structures that are polar at one end and nonpolar at the other end.  

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In chemistry, molecules can be polar or nonpolar. Which of these they are depends on the overall structure that their component chemical bonds (between the atoms present in the molecule) form. Polar molecules, water being a notable example, have positive and negative 'ends' so that when molecules of that substance are physically close the molecules weakly attract each other much like polar magnets would. 

Some chemicals, formed of component molecules, can have a polar end and nonpolar end. For example, soap, when agitated in water, forms chemical structures called micelles that have polar heads and nonpolar tails. The polar heads are water-loving (hydrophilic) and face outward towards the water environment, whereas the nonpolar tails are water - hating (hydrophobic) and huddle inward away from the water. Any greasy fats (lipids) that are in the water get shrouded by the micelles. This is because the fats are also hydrophobic so can escape from the water by joining the nonpolar lining of the micelles and being protected by the polar outer of those micelles. This is how greasy things are cleaned in water using soap (surfactants).

A similar chemical structure to soap micelles, with polar heads and nonpolar tails, can be found in the human body. Cell membranes have hydrophilic phosphate polar heads and hydrophobic lipid nonpolar tails. Nonpolar chemicals like oxygen and CO2 pass through the membrane easily. Larger polar chemicals can only enter and exit by the cell gates. This allows the body to control cell inputs and outputs.

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