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Respiration - Anaerobic respiration

Grade 12IGCSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Anaerobic respiration is the release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen (O2O_2).

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In microorganisms like yeast and in plant tissues, anaerobic respiration is termed fermentation, producing ethanol (C2H5OHC_2H_5OH) and carbon dioxide (CO2CO_2).

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In mammalian muscle cells, anaerobic respiration occurs during vigorous exercise when oxygen demand exceeds supply, resulting in the production of lactic acid (C3H6O3C_3H_6O_3).

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The energy yield of anaerobic respiration is much lower than aerobic respiration, producing only 22 molecules of ATPATP per molecule of glucose (C6H12O6C_6H_{12}O_6), compared to approximately 3636-3838 ATPATP in aerobic conditions.

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Oxygen debt is the volume of oxygen required after exercise to oxidize the accumulated lactic acid in the liver, converting it back into glucose or breaking it down into CO2CO_2 and H2OH_2O.

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Anaerobic respiration takes place entirely within the cytoplasm of the cell and does not involve the mitochondria or the Krebs cycle.

📐Formulae

C6H12O6→2C3H6O3+EnergyC_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + \text{Energy}

C6H12O6→2C2H5OH+2CO2+EnergyC_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}

Glucose→Lactic Acid+Energy (approx. 150 kJ/mol)\text{Glucose} \rightarrow \text{Lactic Acid} + \text{Energy (approx. 150 kJ/mol)}

💡Examples

Problem 1:

Calculate the theoretical number of ATPATP molecules produced from the anaerobic breakdown of 55 molecules of glucose (C6H12O6C_6H_{12}O_6).

Solution:

5×2=105 \times 2 = 10 ATPATP molecules.

Explanation:

Since anaerobic respiration yields a net gain of 22 ATPATP per molecule of glucose, 55 molecules will produce 1010 ATPATP.

Problem 2:

A bread dough rises due to the activity of yeast. Identify the gas produced and the chemical equation representing this process.

Solution:

The gas is Carbon Dioxide (CO2CO_2). The equation is C6H12O6→2C2H5OH+2CO2C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2.

Explanation:

Yeast respires anaerobically (fermentation) using the sugars in the dough. The CO2CO_2 gas bubbles get trapped in the dough, causing it to expand and rise.

Problem 3:

Explain why a sprinter continues to breathe deeply and rapidly for several minutes after a race has ended.

Solution:

To repay the 'Oxygen Debt'.

Explanation:

During the sprint, muscles respired anaerobically, building up lactic acid (C3H6O3C_3H_6O_3). The extra oxygen (O2O_2) inhaled after the race is transported to the liver to help break down or convert the lactic acid, returning the body to its resting state.

Anaerobic respiration - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology