Key concepts:

• As food is broken down in aerobic respiration, the large stores of energy are gently converted to smaller stores in ATP molecules.
• Energy released from the food molecules is used to join together a phosphate group with the molecule adenine diphosphate (ADP), to create the ATP molecule and store energy.
• Elsewhere, the cell is carrying out nonspontaneous, synthetic, joining reactions (such as joining amino acids to form proteins), which require the input of energy.
• Cells use the energy in the ATP molecule to make sure these reactions can take place.
• As the energy in the ATP molecule is transferred to the nonspontaneous reaction, the bond between the last (third) phosphate group and the rest of the ATP molecule is broken, and the ADP molecule and a separate phosphate molecule are formed.
• The ADP molecule and the phosphate molecule are then recycled back to the area where aerobic respiration is taking place, and rejoined together again.
• In this way, ATP and ADP shuttle energy from the food breakdown processes to all the other processes in the cell that require an input of energy.