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Cellular Respiration
Ms. Lew Biology
Chapter 9
Chemical Pathways
Cellular respiration
Basic Need for Energy
Energy in Food:
What is the difference between a:
calorie(lower case c) and Calorie (upper case C)?
-A calorie is the amount of energy needed to raise the
temperature of 1 gram of water by 1 degree C.
-A Calorie is a kilocalorie, or 1000 calories
For example, 1 gram of glucose releases 3811
calories, on a food label 3.8 Calories
Basic Need for Energy
Energy in Food:
Organisms cannot use glucose directly, it must be broken
down into smaller units.
This process in living things begins with glycolysis.
If oxygen is present, glycolysis is followed by the Krebs
Cycle and electron transport chain – This is called Cellular
An Overview:
Cellular Respiration
• The equation for cellular respiration is exactly the
opposite of photosynthesis.
• Equation:
6O2 + C6H12O6  6CO2 + 6H2O and energy
Breaking Down Energy Slowly:
• Glucose needs to be broken down in small steps so that energy is not
• Definition: The process of breaking glucose in half to form 2
molecules of pyruvate (a 3 carbon chain).
• Uses 2 ATP to start reaction
• Produces 4 ATP and 2 NADH
• Does not require oxygen
• Very Fast – thousands of ATP produced in
• Stops when it runs out of NAD+ (electron carrier)
• If oxygen is available: Cellular respiration starts
• If oxygen is NOT available, to make more NAD+,
your body goes through fermentation.
• This way ATP can be made even without Oxygen.
Why use ATP in Glycolysis if you want ATP?
• You have to use a little energy to make even more
• Like a bank, you put money in to earn interest.
• NAD+ and NADH are like NADP+ and NADPH . They can
hold electrons.
• Fermentation is releasing energy in the absence
of oxygen. It is an ANAEROBIC process.
• Ultimately it allows NADH to be converted to
NAD+, allowing glycolysis to continue.
• There are two main types of fermentation
• Alcoholic Fermentation
• Lactic Acid Fermentation
Alcoholic Fermentation
• Alcoholic fermentation is found in Yeasts, and a few
other microorganisms.
• The equation is:
Pyruvic acid + NADH  alcohol + CO2 + NAD+
Note: Carbon Dioxide is also produced, so when yeast
conducts fermentation, there is the release of carbon
dioxide as well as alcohol.
Alcoholic Fermentation
• Alcoholic fermentation diagram
Lactic Acid Fermentation
• Pyruvic acid from glycolysis can be converted to lactic acid.
• This conversion regenerates NAD+ for glycolysis to continue
• The equation is:
Pyruvic acid + NADH  lactic acid + NAD+
Lactic acid fermentation is used by muscles when they run out of
oxygen, ultimately causing soreness.
Lactic acid is also created by unicellular organisms in the production of
cheese, pickles, kimchi and other foods.
Lactic Acid Fermentation
• Lactic Acid fermentation diagram
Krebs Cycle
• In the Krebs Cycle, pyruvic acid is broken down into carbon dioxide.
Krebs Cycle
• Where does it occur:
• It requires oxygen –
• It is also known as
the Citric Acid Cycle
Krebs Cycle
So far, from 1 glucose
Glycolysis produced:
2 NADH and 2 ATP
Krebs Cycle produced:
8 NADH and 2 FADH2 and 2 ATP
Krebs Cycle
What happens to the Krebs cycle products?
Carbon Dioxide is released to the atmosphere
ATP is used for cellular activities
NADH and FADH2 are used in the electron transport chain to
produce large amounts of ATP
Electron Transport Chain
• Uses the high energy
electrons from the
Krebs cycle to convert
ADP into ATP
Electron Transport Chain
• Where does it occur: Inner membrane of the Mitochondria
• It requires oxygen – it is AEROBIC
Electron transport chain
Cellular Respiration totals
So far, from 1 glucose
2 ATP +
Krebs Cycle:
2 ATP +
Electron Transport:
32 ATP
36 ATP from 1 glucose
This is 38% efficiency
The rest of the energy is released as heat
Energy use by humans
Cells contains small amounts of ready ATP
-About 5 seconds worth
After that, your body uses lactic acid formation
-This lasts for about 90 seconds
-You breathe hard to get rid of the lactic acid buildup
For exercise longer than 90 seconds, cellular respiration is
-This is a slow method to generate ATP
-Glycogen (a form of carbohydrate) is used for the first 15-20 minutes
of cellular respiration
-After that other molecules, such as fats, are broken down