Energy

– needed for:   – movement
– synthesis of complex compounds
– active transport

Food

– provides energy needed by cells
– broken down > heat (body heat, excess removed)
chemical storage form

Cellular Respiration

– is the process by which chemical energy stored in food (usually glucose, but may be protein and lipids is released by cells to be used to carry out life processes (ex: locomotion, cell division, active transport)

– takes place in a series of steps involving many enzymes located in mitochondria

Energy Storage and Release

Two steps involved:

1. breakdown of glucose leads to storage of energy in ATP

2. breakdown of ATP provides cell with energy

ANAEROBIC RESPIRATION (Fermentation)

• · release of energy stored in food molecules such as glucose without oxygen
• · very in efficient process à glucose is only partially broken down
• · occurs in yeast, certain bacteria, fungi and active muscle cells

A. Glycolysis (splitting of glucose)

• · through a series of steps, glucose, which is a six-carbon compound (C₆H₁₂O₆) is converted

into two three-carbon compounds of pyruvic acid.

• · this results in a net gain of 2 ATP

glucose   ————–>  2 pyruvic acid

(Note: net yield is 4 ATP-2ATP = 2ATP)

B. Next, carbon dioxide and ethanol (ethyl alcohol) or lactic acid are produced without the yield of any additional energy.

pyruvic  ————–> carbon dioxide + ethanol or lactic acid

A great deal of energy is still present in the ethanol or lactic acid molecules.

C. Summary of Alcohol Fermentation

glucose ————–> ethanol + carbon dioxide + 2 ATP

D. Lactic Acid Fermentation

• · produced in some bacteria and fungi
• · also occurs in active muscles, where anaerobic respiration occurs.
• · accumulation of lactic acid results in muscle fatigue and muscle pain

glucose ————–> lactic acid + carbon dioxide + 2 ATP

AEROBIC RESPIRATION

• · respiration requiring oxygen
• ·efficient process —> glucose is completely broken down to carbon dioxide and water
• · involves two stages:

A. Glycolysis (Anaerobic phase)

B. Kreb’s Cycle or Citric Acid Cycle (Aerobic Phase)

• · the pyruvic acid molecule from glycolysis undergo a series of chemical reactions which result in the formation of CO₂ and H₂O.
• · energy is released in small units and stored in 36 ATP molecules.

C. Net Yield of Energy from One Molecule of Glucose:

From:

i) Glycolysis: 2 ATP (Anaerobic)

ii)      Kreb’s Cycle: 36 ATP (Aerobic)

Total: 38 ATP

D. Word Equation for Aerobic Respiration:

glucose + oxygen    ———-> carbon dioxide + water + 38 ATP

E. Chemical Equation for Aerobic Respiration:

C₆H₁₂O₆ + 6O₂ ———–> 6 CO₂ + 12 H₂O + 38 ATP