Fermentation

Fermentation

7.3

Fermentation

Introduction

Fermentation is the incomplete breakdown of glucose in conditions of limited oxygen or without oxygen.
Fermentation is different from aerobic respiration in its metabolic pathway after the glycolysis stage.
After glycolysis, the pyruvate produced will undergo either alcohol fermentation or lactic acid fermentation.

Alcohol Fermentation

The incomplete breakdown of glucose to ethanol, carbon dioxide and energy.
- Glucose \(\rightarrow\) Ethanol + carbon dioxide + energy (210 kJ)

Yeast

Ethanol is used in the making of beer and wine.
The released carbon dioxide makes bread dough rise.

Plants

Paddy plants that grow in waterlogged areas with less oxygen are able to carry out alcohol fermentation.
Ethanol produced in the tissues during the fermentation process is toxic to most plants but the cells of paddy plants have a higher tolerance for ethanol compared to other species.
Paddy plants produce plenty of alcohol dehydrogenase enzymes that can break down ethanol molecules into non-toxic carbon dioxide.

Lactic Acid Fermentation

The breakdown of glucose into lactic acid and energy.
- Glucose \(\rightarrow\) Lactic acid + energy

Lactobacillus

The bacteria Lactobacillus carries out milk fermentation to produce yoghurt.
Lactobacillus acts on the lactose (milk sugar) and turns it into lactic acid.
The lactic acid will then coagulate casein (milk protein) to produce yoghurt.
Lactic acid is the source of a sour taste in yoghurt.

Human Muscle Cells

This process is carried out by the muscle cells during vigorous training.
During vigorous training, the rate of oxygen used exceeds the oxygen supplied by the blood circulatory system.
The muscle is in an oxygen-deficiency state and is said to undergo oxygen debt.
During this process, glucose cannot break down completely.
For each glucose molecule that is broken down, only two ATP molecules or 150 kJ energy will be produced.
The produced lactic acid accumulates until it reaches a level of concentration that can cause fatigue and muscle cramps.
Once the vigorous activity stops, the intake of excess oxygen will oxidise the lactic acid into carbon dioxide, water and energy. When all the lactic acid has been expelled, the oxygen debt is repaid.

Similarities Between Aerobic Respiration and Fermentation

The breakdown process of glucose and its conversion to chemical energy.
The process begins in the cytoplasm.
Occurs in yeast, bacteria, animals and plants.
Produces chemical energy in the form of ATP.
The process begins with glycolysis when glucose is converted to pyruvate.

Differences between Aerobic Respiration and Fermentation
Aerobic respiration	Fermentation
The breakdown process of glucose is completed in the presence of oxygen.	The breakdown process of glucose is incomplete without oxygen or in limited oxygen conditions
Occurs in cytoplasm and mitochondrion.	Occurs in cytoplasm.
Produces water.	Does not produce water.
Glucose is oxidised completely into carbon dioxide and water.	Glucose is not oxidised completely into ethanol and carbon dioxide or lactic acid.
One molecule of glucose generates 2898 kJ of energy	One molecule of glucose generates 210 kJ (alcoholic fermentation) or 150 kJ (lactic acid fermentation) of energy.

Fermentation

7.3

Fermentation

Introduction

Fermentation is the incomplete breakdown of glucose in conditions of limited oxygen or without oxygen.
Fermentation is different from aerobic respiration in its metabolic pathway after the glycolysis stage.
After glycolysis, the pyruvate produced will undergo either alcohol fermentation or lactic acid fermentation.

Alcohol Fermentation

The incomplete breakdown of glucose to ethanol, carbon dioxide and energy.
- Glucose \(\rightarrow\) Ethanol + carbon dioxide + energy (210 kJ)

Yeast

Ethanol is used in the making of beer and wine.
The released carbon dioxide makes bread dough rise.

Plants

Paddy plants that grow in waterlogged areas with less oxygen are able to carry out alcohol fermentation.
Ethanol produced in the tissues during the fermentation process is toxic to most plants but the cells of paddy plants have a higher tolerance for ethanol compared to other species.
Paddy plants produce plenty of alcohol dehydrogenase enzymes that can break down ethanol molecules into non-toxic carbon dioxide.

Lactic Acid Fermentation

The breakdown of glucose into lactic acid and energy.
- Glucose \(\rightarrow\) Lactic acid + energy

Lactobacillus

The bacteria Lactobacillus carries out milk fermentation to produce yoghurt.
Lactobacillus acts on the lactose (milk sugar) and turns it into lactic acid.
The lactic acid will then coagulate casein (milk protein) to produce yoghurt.
Lactic acid is the source of a sour taste in yoghurt.

Human Muscle Cells

This process is carried out by the muscle cells during vigorous training.
During vigorous training, the rate of oxygen used exceeds the oxygen supplied by the blood circulatory system.
The muscle is in an oxygen-deficiency state and is said to undergo oxygen debt.
During this process, glucose cannot break down completely.
For each glucose molecule that is broken down, only two ATP molecules or 150 kJ energy will be produced.
The produced lactic acid accumulates until it reaches a level of concentration that can cause fatigue and muscle cramps.
Once the vigorous activity stops, the intake of excess oxygen will oxidise the lactic acid into carbon dioxide, water and energy. When all the lactic acid has been expelled, the oxygen debt is repaid.

Similarities Between Aerobic Respiration and Fermentation

The breakdown process of glucose and its conversion to chemical energy.
The process begins in the cytoplasm.
Occurs in yeast, bacteria, animals and plants.
Produces chemical energy in the form of ATP.
The process begins with glycolysis when glucose is converted to pyruvate.

Differences between Aerobic Respiration and Fermentation
Aerobic respiration	Fermentation
The breakdown process of glucose is completed in the presence of oxygen.	The breakdown process of glucose is incomplete without oxygen or in limited oxygen conditions
Occurs in cytoplasm and mitochondrion.	Occurs in cytoplasm.
Produces water.	Does not produce water.
Glucose is oxidised completely into carbon dioxide and water.	Glucose is not oxidised completely into ethanol and carbon dioxide or lactic acid.
One molecule of glucose generates 2898 kJ of energy	One molecule of glucose generates 210 kJ (alcoholic fermentation) or 150 kJ (lactic acid fermentation) of energy.