3.7 Cell Respiration

3.7.1  Define cell respiration

Cell respiration is the controlled release of energy from organic compounds in cells to form ATP (adenosine triphosphate)

3.7.2  State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP

Glycolysis is the breakdown of one molecule of glucose (6C) into two molecules of pyruvate (2 x 3C) with a small net yield of ATP (2 molecules of ATP)

  • This process also results in the reduction of two hydrogen acceptors (NAD+) to form 2 molecules of NADH + H+

3.7.3  Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP

Anaerobic respiration occurs in the absence of a ready supply of oxygen (e.g. during intense physical activity, when oxygen reserves are depleted)

In order to generate the small amounts of energy provided by glycolysis, the end product (pyruvate) must be converted into another substance before more glucose can be used

  • This is because the conversion of pyruvate replenishes the levels of the hydrogen acceptor (NAD+) needed for glycolysis to occur

Anaerobic Respiration

The conversion of pyruvate occurs in the cytoplasm of the cell and the products are:

  • Lactate (3C) in animal cells
  • Ethanol (2C) and carbon dioxide (CO2) in plants, fungi (e.g. yeast) and bacteria
  • The conversion of pyruvate into ethanol and CO2 is also known as fermentation

3.7.4  Explain that, during aerobic cell respiration, pyuvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP

Aerobic respiration occurs in the presence of oxygen and takes place in the mitochondrion

Pyruvate is broken down into carbon dioxide and water and a large amount of ATP is formed (34 - 36 molecules)

Although this process begins with glycolysis (to break down glucose into pyruvate), glycolysis does not require oxygen and is an anaerobic process

Anaerobic versus Aerobic Respiration