8.S.V.2

Living cells get most of their energy through chemical reactions. All living cells make and use carbohydrates (carbon and water), the simplest of these being sugars. All living cells make and use proteins, often very complex compounds containing carbon, hydrogen, oxygen, and many other elements. Making these compounds involves chemical reactions which need water, and take place in and between cells, across cell walls. The reactions also need catalysts called “enzymes.” Many cells also make fats, which store energy and food.