11.1. Respiration

Using Energy

• Respiration is a chemical process that involves the breakdown of nutrient molecules (specifically glucose) in order to release the energy stored within the bonds of these molecules
  • Respiration is enzyme-controlled
• Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically).
  • Much less energy is released for each glucose molecule broken down anaerobically compared to the energy released when it is broken down aerobically
• Respiration occurs in all living cells; most of the chemical reactions in aerobic respiration take place in the mitochondria
• Humans need the energy released during respiration carry out many processes
  • Muscle contraction
  • Protein synthesis
  • Cell division (to make new cells)
  • Growth
  • Active transport across cell membranes
  • Generation of nerve impulses
  • Maintaining a constant internal body temperature

Aerobic Respiration

Aerobic respiration is where energy is released by combining glucose with oxygen.

Most of the time our cells release energy by combining glucose with oxygen. This is called aerobic respiration. Most of the steps of Aerobic Respiration take place in the mitochondria. These steps are controlled by enzymes.

Anerobic Respiration

Anerobic Respiration is where energy is released without using oxygen.

Anaerobic respiration can release energy from glucose without using oxygen, but it is less efficient than aerobic respiration and occurs in the cytoplasm of a cell.

Yeast, a single-celled fungus, can carry out anaerobic respiration by breaking down glucose into alcohol: glucose → energy + alcohol + carbon dioxide

Anaerobic respiration can produce carbon dioxide and is used by plants for short periods of time. Some cells in the human body, like muscle cells, can also perform anaerobic respiration by producing lactic acid instead of alcohol and without producing carbon dioxide. This occurs during vigorous exercise when muscles are using more oxygen than is being supplied, and allows the cells to release some energy from glucose without oxygen until oxygen is available again.

glucose → energy + lactic acid