Cellular respiration has three main stages - glycolysis, the citric acid cycle, and the electron transport chain. Glycolysis breaks down glucose into pyruvic acid, producing a small amount of ATP. Pyruvic acid then enters the citric acid cycle in the mitochondria, producing more ATP and electron carriers. These electron carriers transport electrons through the electron transport chain, producing the most ATP through oxidative phosphorylation as electrons are transferred to oxygen as the final electron acceptor.

1. Getting energy to make ATP
Cellular Respiration
The process by which mitochondria break
down food molecules to produce ATP is called
cellular respiration.
There are 3 stages of cellular respiration.
1. Glycolysis (anaerobic)
2. The citric acid cycle
3. The electron transport chain. (aerobic)

2. Glycolysis
Energy used and made in glycolysis
Takes 2 ATP to start glycolysis
Only 4 ATP are produced
4-2= 2 ATP gained (not very effective)
Glycolysis uses an electron carrier called NAD+.
NAD+ forms NADH which it accepts 2 electrons.

3. Glycolysis
Glycolysis is a series of chemical reactions in the
cytoplasm of a cell that breaks down glucose
into 2 molecules of pyruvic acid.
Glucose 2 pyruvic acid
Glucose is a 6 carbon molecule.
Pyruvic acid is a 3 carbon molecule.

4. Glycolysis
• Before citric acid cycle and electron transport
chain stages begin, pyruvic acid undergoes a
series of reactions in which it gives off a
molecule of CO2 and bines with a molecule
called coenzyme A to form acetyl-CoA.

6. The citric acid cycle
• Occurs in the mitochondria
Citric acid cycle also called Krebs cycle
For every turn of the cycle, 1 ATP molecule of
ATP and 2 molecules of carbon dioxide are
produced.
NAD+ and FAD+ (electron carriers) form NADH
and FADH2 (carry electrons to electron transport
chain)

8. Electron Transport chain
• Occurs in the inner membrane of the
mitochondrion.
• Energized electrons are carried by NADH and
FADH2 to the top of the chain.
• The electrons are passed from protein to
protein within the membrane, slowly releasing
their energy in steps. Some of that energy is
used directly to form ATP.

9. Electron Transport Chain
• The final electron acceptor at the bottom of
the chain is oxygen, which reacts with four
hydrogen ions (4H+) and four electrons to
form two molecules of (H2O). This is why
oxygen is so important to our bodies.
• Without oxygen, the proteins in the electron
transport chain cannot pass along the
electrons.

10. Electron Transport Chain
• If a protein cannot pass along an electron to
oxygen, it cannot accept another electron.
Very quickly, the entire chain becomes
blocked and ATP production stops.
• Overall, the electron transport chain add 32
ATP molecules.
• Aerobic process of ATP is very effective.

12. Other ways to make ATP
Fermentation
Fermentation occurs after glycolysis.
Is a process of making ATP when there is no
oxygen present. (Anaerobic process)
Ex. Happens during heavy exercise, when your
cells are without oxygen for a short period of
time.

13. Fermentation
• There are two major types of fermentation
1. Lactic acid fermentation
2. Alcoholic fermentation

14. Lactic acid fermentation
• Lactic acid fermentation is one of the
processes that supplies energy when oxygen is
scarce.
• Two molecules of pyruvic acid produced in
glycolysis use NADH to form two molecules of
lactic acid. This releases NAD+ to be used in
glycolysis, allowing 2 ATP molecules to be
formed for each glucose molecule.

15. Lactic acid fermentation
• The soreness feeling you get after you
workout is due to the build up of lactic acid in
the muscles cells.
• The lactic acid is transferred from muscle cells,
where it is produced during strenuous
exercise, to the liver that converts it back to
pyruvic acid.

16. Alcoholic fermentation
• Is used by yeast cells and some bacteria to
produce CO2 and ethyl alcohol.
Ex. When making bread, yeast cell produce CO2
that forms bubbles in the dough.