KA6

• The chemical energy stored in glucose must be released by all cells through a series of enzyme-controlled reactions called respiration.
• The energy released from the breakdown of glucose is used to generate ATP.
• Energy released during respiration is used for cellular activities such as:

  -muscle contraction

  -cell division

  -protein synthesis

  -active transport

  -carbon fixation

  -transmission of nerve impulses
• Aerobic Respiration:

  glucose + oxygen———-> carbon dioxide+ water + energy

  Aerobic respiration occurs only when oxygen is present. It begins in the

  cytoplasm and is completed in the mitochondrion. It produces a large number

  of ATP.
• Fermentation:

  In plants/yeast:- glucose ———>carbon dioxide + ethanol + energy

  In animals (muscles):- glucose———-> lactate + energy

  Fermentation occurs when oxygen is absent. It occurs and is completed in the

  cytoplasm. It produces 2 molecules of ATP (so less efficient).
• Aerobic Pathway:

  Stage 1

  Firstly, glucose is broken down into two

  molecules of pyruvate.

  This releases enough energy to yield two

  molecules of ATP.

  This stage occurs in the cytoplasm of a

  cell
• Aerobic Pathway: Stage 2

  Then, if oxygen is present, aerobic

  respiration takes place.

  Each pyruvate is broken down into

  carbon dioxide and water.

  This releases enough energy to yield a

  large number of ATP molecules.

  Cells requiring a lot of energy will have a higher number of mitochondria.

  Such cells include muscle, sperm & nerve cells (neurons) in animals and

  companion cells in plants.
• Fermentation:

  Stage 1

  In the absence of oxygen, the

  fermentation pathway takes place.

  Glucose is broken down into two

  molecules of pyruvate.

  This releases enough energy to yield two

  molecules of ATP
• Fermentation: Stage 2

  In plants and yeast cells, the pyruvate is converted to carbon dioxide and

  ethanol.

  In animals cells (e.g. muscle cells), the pyruvate is converted to lactate.

  The whole fermentation pathway occurs in the cytoplasm of a cell.

  Fermentation yields only 2 molecules of ATP from the initial breakdown of

  glucose into pyruvate
• Stage 1 of respiration

  
• Stage 2 of respiration

  
• Stage 1 of fermentation (animal cell)

  
• stage 2 of fermentation (plant and yeast cells)