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Introduction to Respiration

Biology: Cambridge International A Level, topic 12.2.1

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.

Importance of respiration

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
Types of respiration

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).
Glycolysis

Glycolysis

Anaerobic respiration

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.
Aerobic respiration

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.

Phosphorylation

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).
Oxidation

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.
Net gain

Net gain

  • 2 ATP molecules.
  • 2 NADH molecules.

Test yourself on Introduction to Respiration

  • What are the two types of respiration?

  • What stage do both types of respiration (aerobic and anaerobic) start with?

  • Which of the following statements about anaerobic respiration are true?

  • What is the net gain of glycolysis?

  • Which of the following statements about glycolysis are true?

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