Chapter 9:
Cellular
Respiration
Nutrition
• Energy in most food originally comes from the sun
• 2 ways to get food
– Autotrophs or Producers
• Make their own food
• Uses photosynthesis or chemosynthesis
• Examples: plants, algae, some bacteria
– Heterotrophs or Consumers
• Cannot make their own food
• Take in food by eating
• Examples: animals, protists, fungi, most
bacteria
Cell Respiration
• Occurs in ALL living organisms
• Process in which mitochondria
break down food molecules
(sugars) to produce ATP
• 3 stages occur in cellular
respiration: glycolysis, Krebs
cycle, and electron transport chain
Glycolysis
• Takes place in the cytoplasm of
a cell
• Breaks down glucose to make 2
molecules of pyruvic acid and
NADH
• Needs 2 ATP molecules to start
glycolysis
• Produces 4 ATP molecules
• 4-2=2 ATP gained (releases
only a small amount of energy)
• This is an anaerobic
process: does not require
Oxygen
Glycolysis
If Oxygen is
present
Aerobic
Respiration
If Oxygen is not
present
Fermentation
Anaerobic Respiration
• Fermentation  occurs in the absence of
oxygen (2 kinds)
• Alcoholic Fermentation  yeasts
– Produces carbon dioxide gas and ethyl alcohol
– Ex: wine, bear, breads
Lactic Acid Fermentation
• Transferred from muscles (occurs in muscle cells)
• Produced during strenuous activity/exercise
– Results in muscle soreness
• Examples in food: yogurt, buttermilk, cottage
cheese, sour cream
• No additional ATP molecules are
produced
• Only 2 ATP produced from glycolysis
and anaerobic respiration
Aerobic Respiration
• Occurs in the
mitochondria
• Yields 36 ATP molecules
• 3 steps of aerobic
respiration
– Pyruvic Acid
conversion
(glycolysis)
Krebs Cycle (Citric Acid Cycle)
• Breaks down glucose
• Acetyl CoA  citric acid (2 ATP
produced) + CO2
Electron Transport Chain
• Produces 34 ATP
• Converts ADP to ATP
• 1 glucose molecule  38 ATP
–2 from glycolysis
–36 from Krebs cycle and Electron
Transport Chain
Photosynthesis vs. Cellular Respiration
Photosynthesis
Cellular Respiration
What does it
do?
Makes glucose
Breaks down glucose
Why do it?
To store energy
To release energy
Who does it
involve?
“green organisms”, some
bacteria, algae, plants
ALL organisms
When does it
occur?
The day into night
All the time
Where does it
occur?
Chloroplasts
Starts in the cytoplasm
Ends in the mitochondria
in the presence of O2
Equation for
process
6CO2 + 6H2O + light 
C6H12O6 + 6O2
C6H12O6 + 6O2  6CO2 +
6H2O + ATP
Exchange of
gases
Takes in CO2 and gives off Takes in O2 and gives off
O2
CO2
Review:
1. Identify which phrase describes the following:
lactic acid fermentation
alcoholic fermentation
________ important in baking bread
________ builds up in muscles after a few seconds of intense
activity
________ the reasons why runners breathe heavily after a
race
________ involves in making beer and wine
2. What is the net energy gain in glycolysis?
a. 4 ATP
b. 2 ATP
c. 36 ATP
d. 38 ATP
Bell Ringer:
1. Glycolysis produces a net gain of _____ ATP
molecules for each reaction.
2. Identify if the phrase below is describing
photosynthesis or cellular respiration:
________ reactants are CO2 and H2O
________ occurs only in plants, algae, and some
microorganisms
________ 6O2 +C6H12O6  6CO2 + 6H2O + Energy
________ uses oxygen to release energy from food
3. What is another name for the Krebs cycle?
a. Glycolysis
c. Citric acid cycle
b. Alcoholic fermentation
d. Respiration