Class Notes 3:
Cellular Respiration: How cells
make ATP
I. Step 1: Glucose enters the cell
A.
B.
In plants, it has been made by
photosynthesis.
In animals, it has been eaten.
II. Step 2: Glycolysis
The glucose is
broken in half into
2 molecules called
pyruvic acid.
(C6H12O6  2C3H6O3
 2C3H4O3 )
B. Uses 2 ATP, but
makes 4.
A.
III. Step 3: Kreb’s cycle (citric acid
cycle)
A.
Takes place in the mitochondria
B. The Krebs cycle is a
series of chemical
reactions that takes
the energy from the
pyruvic acids and
passes it to other
molecules.
1. CO2 is released as
waste.
2. Two ATP are made.
IV. Step 4: Electron Transport Chain
The high energy molecules from the
Kreb’s Cycle are used to create 32
ATP.
B. Oxygen is used to accept the electrons,
so this is an aerobic process.
C. Water and heat are released as waste.
D. The formula for cellular respiration is
C6H12O6 + 6O2  6H2O + 6CO2 + (ATP)
A.
V. Lactic Acid Fermentation
During times of strenuous activity (weight lifting,
sprinting), your body can’t get enough oxygen.
B. Fermentation allows glycolysis to continue
without oxygen (anaerobic).
C. Creates a small amount of ATP.
D. Pyruvic Acid is converted to Lactic Acid.
A.
Summary
What are the 4 steps of cellular
respiration?
What is the difference between aerobic
and anaerobic respiration?