6.2.2 anaerobic respiration - alcohol fermentation - lactic acid fermentation

1. 6.2.2 Anaerobic
respiration
Ong Yee Sing
2017

2. Objectives
• Understanding the process of aerobic respiration
• Understanding the importance of anaerobic respiration

3. Anaerobic respiration 无氧呼吸
• from Greek an ‘not’ + aēr ‘air’+ bios ‘life’ + -
ic.
• Also known as fermentation发酵作用.
• Occurs temporally in animals and plants, but
some microbes such as anaerobicbacteria厌氧
菌 only carry out anaerobic respiration.
• Anaerobic respiration is the process of
producing cellular energy without oxygen.
• Anaerobic respiration is a relatively fast
reaction and produces 2 ATP, which is far
fewer than aerobic respiration.
• Anaerobic respiration occurs in the
cytoplasm.
• The end products of anaerobic respiration
may be ethanol乙醇 + carbon dioxide or lactic
acid乳酸.

4. Anaerobic respiration in the industry

5. Quiz
• During anaerobic respiration, the breakdown of glucose is...
A. incomplete
B. complete
C. indifferent
D. slow

7. Lactic acid fermentation
• Occurs in skeletal muscle,
endoparasites (e.g. Ascaris
蛔虫, tapeworm绦虫) and
lactobacillus乳酸菌/乳杆菌.
• Example of food produced
are kimchi, yogurt, cheese.
Glucose  2 Pyruvate  2 Lactate + 2 ATP
Lactic acid is lactate + H+lactobacillus

8. Lactic acid fermentation in animal
• As our bodies perform strenuous exercise, the muscles may require more
energy production than our bodies can adequately deliver oxygen.
• Hence, on top of aerobic respiration, the muscle cells also carry out
anaerobic respiration.
• Accumulated lactic acid increases in the acidity of the muscle cells and
causes pain and muscular fatigue疲劳(decline in ability of a muscle to generate force).
• Lactic acid can be converted to glucose in the liver in the presence of
oxygen.
Cori cycle (Lactic acid cycle)
糖原生成
糖酵解

9. Oxygen debt氧债
• Oxygen debt is the extra
oxygen that must be used in
the oxidative energy processes
after a period of strenuous
exercise to reconvert lactic
acid to glucose.
• Hence, after exercise, the
oxygen debt is "repaid" by
rapid, deep breathing.

10. Quiz
• Muscle soreness and fatigue is caused by
A. alcoholic fermentation
B. lactic acid fermentation
C. glycolysis
D. chemiosmosis

11. Alcohol fermentation
• Occurs in temporally
submerged plants, yeast
and Aspergillus曲霉.
• Example of food
produced are alcoholic
drinks, bread, cakes.
Glucose  2 Pyruvate  2 Ethanol + 2 CO2 + 2 ATP
yeast

12. Alcohol fermentation in plants
• In waterlogged habitat or
flooded area, the roots of the
plants are submerged in water
and the supply of oxygen to the
roots is cut off.
• Under this condition, the
plants can only carry out
anaerobic respiration.
• Increased concentration of
ethanol will disturb the
chemical balance (acidify the
cell) in the plant cell and lead
to cell death.
Three fermentative pathways of plants: alcoholic
fermentation, lactic fermentation and the alanine
pathway.s

13. Summary
Lactic acid fermentation Alcoholic fermentation

14. Quiz
• Where in the cell does anaerobic respiration take place?
A. Nucleus
B. Cytoplasm
C. Mitochondria
D. Cell membrane

15. Comparison of aerobic respiration and
anaerobic respiration
Aerobic respiration Anaerobic respiration
Organism or organ involved Most organisms Some fungi such as yeast, anaerobic
bacteria; some endoparasitic worms;
higher animals during diving and vigorous
exercise of skeletal muscles.
Site or organelle Mitochondrion Cytoplasm
ATP produced from one
molecule of glucose
36/38 ATP* 2 ATP
Respiratory products Carbon dioxide + water Animals: lactic acid
Plant & yeast: ethanol + carbon dioxide
Oxidation of glucose Complete Incomplete
*certain cells such as the heart and liver cells have a net gain of 38 ATP, this is because ATP is not
required in the process of transporting the NADH produced during glycolysis into the mitochondrion.

16. Quiz
• NADH is produced during
A) glycolysis
B) the oxidation of pyruvate
C) the Krebs cycle
D) all of the above
E) none of the above