12.2.1

Introduction to Respiration

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Respiration

Respiration is a series of reactions that convert chemical energy stored in carbohydrates into ATP. It takes place in the mitochondria of eukaryotic cells.

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Importance of respiration

  • Respiration is the process that converts energy within the bonds of glucose into a more readily available form: ATP. The equation for respiration is:
    • 6O2 + C6H12O6 (glucose) → 6CO2 + 6H2O
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Types of respiration

  • There are two types of respiration:
    • Aerobic - respiration using oxygen.
    • Anaerobic - respiration without oxygen.
  • Both types of respiration start with the same stage: glycolysis (pictured).
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Anaerobic respiration

  • Anaerobic respiration does NOT use oxygen (e.g. short burst of intense exercise).
  • There are two types of anaerobic respiration:
    • Ethanol fermentation - takes place in plants and yeast.
    • Lactate fermentation - takes place in animals.
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Aerobic respiration

  • Aerobic respiration uses oxygen (e.g. extended periods of exercise).
  • The reaction and products are the same in plants, animal and yeast.
  • Aerobic respiration also differs from anaerobic respiration in the following ways:
    • Water is produced.
    • More ATP is produced.
    • Glucose is fully broken down.
    • After glycolysis, there are more steps (the link reaction, the Krebs cycle and oxidative phosphorylation).

Glycolysis

Respiration produces ATP and can be either aerobic or anaerobic. Glycolysis is the first stage in both these processes. Glycolysis happens in the cytoplasm and is an anaerobic process.

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Phosphorylation

  • The first step in glycolysis involves the phosphorylation of glucose to glucose phosphate using one molecule of ATP.
  • Glucose phosphate is phosphorylated by another molecule of ATP to hexose bisphosphate (a six-carbon molecule)
  • Hexose bisphosphate splits into two molecules of triose phosphate (TP).
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Oxidation

  • The two molecules of TP are oxidised to pyruvate (another three-carbon molecule) in a multi-step reaction.
  • A single TP molecule produces two molecules of ATP and one molecule of reduced NAD (NADH) in this process.
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Net gain

  • 2 ATP molecules.
  • 2 NADH molecules.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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