Organisms need energy for: • chemical reactions to build larger molecules…

The idea

The energy transferred by respiration is not used only for movement. It powers chemical reactions that build larger molecules from smaller ones, such as joining amino acids into proteins or glucose units into starch and cellulose. It also enables movement, including muscle contraction, cilia beating and the movement of substances across membranes. In mammals and birds, some energy is transferred to the surroundings to keep the body at a constant warm temperature, which supports enzyme activity. For example, a growing plant uses energy to build cellulose for cell walls, a running mammal uses energy for muscle contraction, and a resting bird uses energy to maintain its body temperature. All three uses depend on respiration supplying energy in the form of ATP.

What earns the marks

• Energy from respiration is used in chemical reactions that build larger molecules from smaller ones.
• Examples of building larger molecules include making proteins from amino acids and making starch or cellulose from glucose.
• Energy is needed for movement, including muscle contraction and other cellular movement.
• Energy is transferred to keep warm in mammals and birds, maintaining a suitable body temperature.
• The three named uses are chemical reactions to build larger molecules, movement and keeping warm.

Common mistakes and how to put them right

• Thinking energy is used only for movement.

  Put it right by naming building larger molecules and keeping warm as additional uses.

• Confusing building larger molecules with breaking down food.

  Put it right by stating that respiration energy drives synthesis reactions such as protein formation.

• Assuming all organisms use energy to keep warm.

  Put it right by linking keeping warm mainly to mammals and birds, while all organisms use energy for synthesis and movement.

Exam tips

• Give a named example for each use, such as protein synthesis, muscle contraction and maintaining body temperature.
• Link each use back to energy transferred by respiration rather than to food directly.
• Use the phrase build larger molecules when describing synthesis, and support it with a specific molecule such as protein or cellulose.