cellular respiration

• Definition of cellular respiration :

  • A series of metabolic processes that take place within a cell in which the biochemical energy is harvested from organic substance (e.g. glucose) and then stored in energy-carrying biomolecule (e.g. ATP) for use in energy-requiring activities of the cell
• Cellular respiration


  Occurs in the mitochondria and cytoplasm of all living cells
• Glucose


  The starting point that we get from the food that we eat, a type of simple sugar which can be broken down into water and carbon dioxide thus releasing the energy that held the glucose molecule together
• Types of respiration

  • Aerobic (uses oxygen)
  • Anaerobic (does not need oxygen)
• Aerobic respiration

  Glucose + oxygen > carbon dioxide + water (+ energy released)
• The chemical equation for aerobic respiration is: C6H12O6 + 6O2 > 6CO2 + 6H2O + energy
• Respiration is a series of reactions, but this summarises the overall process
• • The energy released forms ATP (adenosine triphosphate). This is formed from ADP (adenosine diphosphate) using the energy released from the breakdown of glucose.

  • ATP can be quickly broken back down to ADP, thus releasing the energy again.

  • Cellular respiration is a complex series of chemical reactions that release enough energy to turn ADP into ATP. Any energy released that is not enough to generate ATP is given off as heat which we use to maintain our body temperature at around 37 C.
• there are 3 stages to cellular respiration:

  1. Glycolysis. This occurs in the cytoplasm of the cell. It involves the breakdown of glucose into pyruvate (pyruvic acid) with some energy.
  2. Krebs cycle (or citric acid cycle). This is a complex series of reactions which result in more energy being released to produce more ATP and occurs in mitochondria (cell organelles)
  3. Electron transport chain. This occurs in the walls of the mitochondria and requires oxygen, (hence aerobic respiration). Carbon dioxide is a by-product.
• Anaerobic respiration


  1. Pyruvic acid broken down into lactic acid

  2. No oxygen required
• Glucose → lactic acid (+ energy released)
• Anaerobic respiration


  • Occurs when we need extra supplies of ATP, eg when exercising
  • Happens as an additional process to supplement the energy produced by aerobic respiration, not as an alternative
• Lactic acid

  • Poisonous
  • Build up in muscles causes fatigue
• Lactic acid build up


  Causes an oxygen debt - we need to break down the lactic acid in the mitochondria using oxygen
• Anaerobic respiration produces less energy than aerobic respiration - about 2 molecules of ATP rather than 38 as the glucose is not fully broken down
• cellular respiration


  adenosine triphosphate, or ATP as it is commonly known, is a high energy molecule found in every cell. Its job is to store and supply the cell with energy it needs. It is sometimes called the energy currency of the body.

  Cellular respiration is a complex set of chemical reactions and processes that take place in the mitochondria to convert biochemical energy from nutrients into ATP and then to release waste products.

  There are two types of respiration that take place inside cells to provide energy:

  • Aerobic - uses oxygen
  • Anaerobic - does not need oxygen.
• Aerobic respiration


  • Oxygen and glucose are required for aerobic respiration to take place.

  It produces waste carbon dioxide and water as well as providing energy.

  glucose + oxygen > carbon dioxide + water

  • A sugar called glucose, from our food, is broken down into water and carbon dioxide, and the energy that was holding the glucose molecule together is released.
• Anaerobic respiration


  • This type of respiration takes place if oxygen is not available, but it provides less energy.

  glucose > pyruvate > lactate (when oxygen becomes available)

  • Glycolysis is the process that takes place in the cell cytoplasm that breaks down glucose and forms pyruvate, with the production of two molecules of ATP. Pyruvate can be used in either anaerobic respiration if no oxygen is available or in aerobic respiration via a cycle of chemical reactions that yields much more usable energy for the cell.
• Pyruvate 


  A molecule that is involved in energy generation, it can be either converted to lactate under anaerobic conditions or broken down to water and carbon dioxide in the presence of oxygen, thus generating large amounts of ATP.
• Pyrovic acid supplies energy to cells through the citric acid cycle (also trown as the Krebs cycle) when oxygen is present (aerobic respiration);

  when oxygen is lacking, it ferments to produce lactic acid. The lactic acid neds to be oxidised later to carbon dioxide and water to prevent it building up oxygen doesn't become available cells die, because lactate is toxic.

  Anaerobic respiration is likely to occur when oxygen is in short supply, such as when exercising because muscle cells need a lot of energy.