Cell Biology

Chemical reactionsWhat arechemicalreactions?A simplechemical reactionAll of the millions and millions of different compounds are made ofonly 92 elements combined in different ways. Just as you can spellthousands of words with the same 26 letters, you can make all ofchemicals in the world from just 92 elements. How are all of thesedifferent compounds made? The answer is chemical reactions. Achemical reaction is a process that rearranges the atoms of one ormore substances into one or more new substances.Hydrogen reacts with oxygen to produce water and energy. Howdo we show this chemical reaction? In cooking you start withingredients that are combined to make different foods. In chemicalreactions you start with reactants that are combined to makeproducts. The reactants and products may include atoms,molecules, and energy. Two hydrogen molecules combine with oneoxygen molecule to make two water molecules. Hydrogen andoxygen are the reactants. Water and energy are the products.chemical reaction - a processthat rearranges the atoms of oneor more substances into one ormore new substances.Life useschemicalreactionsCells use many chemical reactions. You might say that life is aseries of chemical reactions (Figure 4.4). Your cells constantlyrearrange molecules to make energy for movement, thinking, andeven sleeping. Plant cells use a chemical reaction to store energyfrom the sun in the form of molecules.Figure 4.4: Life is a series ofchemical reactions.72UNIT 2 CELL BIOLOGY