6.2.2 Anaerobic respirationOng Yee Sing

2017

Objectives

• Understanding the process of aerobic respiration

• Understanding the importance of anaerobic respiration

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.

Anaerobic respiration in the industry

Quiz

• During anaerobic respiration, the breakdown of glucose is...

A. incomplete

B. complete

C. indifferent

D. slow

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 ATPLactic acid is lactate + H+lactobacillus

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

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.

Quiz

• Muscle soreness and fatigue is caused by

A. alcoholic fermentation

B. lactic acid fermentation

C. glycolysis

D. chemiosmosis

Alcohol fermentation

• Occurs in temporally submerged plants, yeastand Aspergillus曲霉.

• Example of food produced are alcoholic drinks, bread, cakes.

Glucose 2 Pyruvate 2 Ethanol + 2 CO2 + 2 ATPyeast

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

Summary

Lactic acid fermentation Alcoholic fermentation

Quiz

• Where in the cell does anaerobic respiration take place?

A. Nucleus

B. Cytoplasm

C. Mitochondria

D. Cell membrane

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.

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