Key concepts:

• Living cells perform both spontaneous and nonspontaneous reactions every second.
• Food molecules are broken down by reacting them with oxygen.
• These are spontaneous reactions that give off energy into the environment. (Just like burning the candle in oxygen).
• Cells also carry out reactions that join together monomers (such as amino acids, sugars, nucleotides, etc.), to form long polymer chains.
• These synthetic, joining, reactions are nonspontaneous and will not take place unless extra energy is added from outside the reaction.
• Cells use the energy given off in spontaneous reactions to join together monomers and so create polymers (like proteins, polynucleotides, polysaccharides, etc.) the need.