Aerobic and anaerobic respiration: Organisms need energy for:

The idea

All living organisms transfer energy from glucose during respiration to power life processes. Energy is needed for chemical reactions that build larger molecules from smaller ones, such as joining amino acids to form proteins or glucose molecules to form starch and cellulose. It is also needed for muscle contraction, so animals can move, and for maintaining a constant internal body temperature in mammals and birds. In plants, energy supports active transport of mineral ions into root hair cells. These processes occur in cells of animals, plants, fungi and bacteria, so respiration is universal. The energy is not used directly from glucose; it is transferred through ATP in cells.

What earns the marks

• Energy is needed for chemical reactions that build larger molecules from smaller ones, including protein synthesis from amino acids and starch or cellulose synthesis from glucose.
• Energy is needed for muscle contraction, enabling movement in animals.
• Energy is needed to maintain a constant internal body temperature in mammals and birds.
• Energy is needed for active transport, such as the uptake of mineral ions by plant root hair cells.

Common mistakes and how to put them right

• Saying energy is needed for breathing rather than for muscle contraction and other cell processes.

  Put it right: Breathing supplies oxygen, while respiration transfers energy for cell activities.

• Listing photosynthesis as a use of energy in animals.

  Put it right: Photosynthesis is a plant process that stores energy, whereas respiration transfers energy for cell activities.

• Writing that energy is made or produced by respiration.

  Put it right: Respiration transfers energy from glucose, and energy is not created.

Exam tips

• Give named examples for each use, such as amino acids forming proteins or root hair cells absorbing nitrate ions.
• Link each use to a specific organism group where relevant, for example muscle contraction in animals and temperature maintenance in mammals and birds.
• Use the phrase 'energy is transferred' rather than 'energy is made' to match scientific conventions.