1. Cellular Respiration: Harvesting Chemical Energy
CHAPTER 4
Cellular Respiration: Harvesting Chemical Energy

2. What if we do not have oxygen?
Without trees and bacteria to make oxygen, we would still be able to make ATP from sugar (just not as much)
Modifications of glycolysis called fermentation reactions are used to release energy

3. Fermentation Reactions
These reactions produce only 2 ATP per glucose molecule and must regenerate NAD+ resulting in the formation of either:
Ethanol and CO2
Lactic Acid

4. In Human Muscle Cells: Lactic Acid Fermentation
Some of your cells can actually work for short periods without oxygen
Pyruvate is converted to lactate.
Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going
In human muscle cells, lactic acid is a by-product
Human muscle cells can make ATP with and without oxygen
They have enough ATP to support activities such as quick sprinting for about 5 seconds
A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds
To keep running, your muscles must generate ATP by the anaerobic process of fermentation

5. In Human Muscle Cells: Lactic Acid Fermentation
Lactic acid is associated with the “burn” you get with heavy exercise.
If too much lactic acid builds up, your muscles give out.
Physical conditioning allows your body to adapt to increased activity.
The muscle cells become more efficient (How?)
The body can increase its ability to deliver oxygen to muscles (How?)
Long-distance runners wait until the final sprint to exceed their aerobic capacity.
Figure 6.1

6. In Microorganisms: Alcohol Fermentation
Various types of microorganisms perform fermentation
The food industry uses yeast to produce various food products
Yeast cells carry out a slightly different type of fermentation pathway
This pathway produces CO2 and ethyl alcohol

7. Alcohol fermentation: A two-step process where CO2 is lost…
Lactic acid fermentation: A single step with no loss of CO2