Cellular respiration is the process by which cells break down glucose and other food molecules in the presence of oxygen to extract energy. It occurs in three main stages: glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis breaks down glucose and produces some ATP. The Krebs cycle further breaks down the products of glycolysis and produces more ATP and electron carriers. The electron transport chain uses these electron carriers to produce large amounts of ATP through chemiosmosis.

1. Chapter 9
Cellular Respiration

2. Chemical Energy
• Living things get energy from the food they
consume
• Calorie – the amount of energy needed to
raise the temperature of 1 gram of water 1
°C
• 1 gram of glucose when burned in the
presence of oxygen releases 3811 C

3. Cellular respiration
• Process that releases energy by breaking
down glucose and other food molecules in
the presence of oxygen (aerobic)
• 6O2 + C6H12O6 → 6CO2 + 6H2O + energy
• Oxygen + glucose → carbon dioxide + water + energy
• Three main stages:
– Glycolysis
– Krebs Cycle
– Electron transport

4. Glycolysis
• The process in which one molecule of
glucose is broken in half producing two
molecules of pyruvic acid; a 3-carbon
compound
• 2 ATP molecules are used to get the
reaction going and will produce 4 ATP
molecules when the process is complete

5. Cont.
• NAD+ (electron carrier) accepts 4 high
energy electrons and becomes NADH
• This process can produce thousands of
ATP molecules in a few milliseconds
• Does not require oxygen (anaerobic)
• Energy is used up quickly

7. Fermentation
• Production of ATP in the absence of
oxygen (anaerobic)
• Two types: Alcoholic fermentation and
Lactic acid fermentation
• Alcohol fermentation: NADH is converted
back to NAD+ by passing high energy
electrons back to pyruvic acid
• Pyruvic acid + NADH → alcohol + CO2 and NAD+

8. Cont.
• Lactic fermentation: NADH is converted
back to NAD+ by passing high energy
electrons back to pyruvic acid and
producing lactic acid
• Lactic acid is produced in muscle when
the body cannot supply enough oxygen
• Pyruvic acid + NADH → lactic acid + NAD+

9. Krebs Cycle
• End of glycolysis, 90% of chemical energy
in glucose is still unused, cell will use
oxygen to extract the remaining energy
• Krebs cycle begins when pyruvic acid
produced by glycolysis enters the
mitochondrion
• Pyruvic acid is used to make carbon
dioxide, ATP, NADH, and FADH2

10. Electron Transport Chain
• Uses the high energy electrons from the
Krebs cycle to convert ADP to ATP
• In eukaryotes: inner membrane of the
mitochondrion
• In prokaryotes: in the cell membrane
• H+ builds up in the intermembrane space
making it positively charged…other side,
is now negatively charged

11. • As H+ escape through membrane, the
mitochondria contain proteins (ATP
synthase) which rotates, the enzyme
grabs the low energy ADP and attaches a
phosphate forming high energy ATP
• Process is repeated over and over

12. Energy for the body
• Quick – gylcolysis or fermentation
• Long term- cellular respiration

13. Summary
• Cellular respiration has 3 stages:
– Glycolysis
– Krebs cycle
• Electron transport chain