1. There are two types of respiration
Aerobic Respiration: respiration with oxygen
Anaerobic Respiration: respiration w/o oxygen

2. Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration requires O2 to produce ATP during chemiosmosis.
However, glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation to produce ATP

3. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
Two common types are
alcohol fermentation (YEAST/BACTERIA)
lactic acid fermentation (HUMANS/ANIMALS)

4. Alcohol Fermentation
In alcohol fermentation, pyruvate is converted to ethanol in two steps,
releasing CO2
Oxidizing NADH
Alcohol fermentation by yeast is used in brewing, winemaking, and baking

5. Alcohol fermentation 2 ADP + 2 P 2 ATP Glucose Glycolysis 2 Pyruvate
LE 9-17a
2 ADP + 2 P
2 ATP i
Glucose
Glycolysis
2 Pyruvate
2 NAD+
2 NADH 2
CO2
+ 2 H+
2 Acetaldehyde
2 Ethanol
Alcohol fermentation

6. Lactic Acid Fermentation
In lactic acid fermentation, to NADH is oxidized with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

7. Lactic acid fermentation
LE 9-17b
2 ADP + 2 P
2 ATP i
Glucose
Glycolysis
2 NAD+
2 NADH 2
CO2
+ 2 H+
2 Pyruvate
2 Lactate
Lactic acid fermentation

8. Fermentation and Cellular Respiration Compared
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
In anaerobic respiration O2 is not used
It serves to oxidize NADH back to NAD+, otherwise it would eventually run out for NAD+ the glycolysis would stop
Aerobic respiration produces much more ATP

9. Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

10. LE 9-18
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol or
lactate
Acetyl CoA
Citric
acid
cycle

11. The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms
Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere