Energy and ATP

• 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.
• The energy transferred by ATP can be used for cellular activities such as
  • muscle cell contraction,
  • cell division,
  • protein synthesis
  • transmission of nerve impulses.

Aerobic Respiration

• Glucose is broken down to two molecules of pyruvate, releasing enough energy to yield two molecules of ATP.
• Further breakdown depends upon the presence/absence of oxygen.
• If oxygen is present, aerobic respiration takes place, and each pyruvate is broken down to carbon dioxide and water, releasing enough energy to yield a large number of ATP molecules.

Fermentation Pathway

• In the absence of oxygen, the fermentation pathway takes place.
• In animal cells, the pyruvate molecules are converted to lactate and in plant and yeast cells they are converted to carbon dioxide and ethanol.
• The breakdown of each glucose molecule via the fermentation pathway yields only the initial two molecules of ATP.

Location of Respiration

• Respiration begins in the cytoplasm.
• The process of fermentation is completed in the cytoplasm whereas aerobic respiration is completed in the mitochondria.
• The higher the energy requirement of a cell the greater the number of mitochondria present in that cell.

Respirometer

• A respirometer measures the rate of respiration in organisms.

Topic Summary