GCSE Biology - Aerobic & Anaerobic Respiration Notes

Respiration

• Respiration: A biochemical process occurring in living cells involving the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.

• Cellular respiration: An exothermic reaction that transfers energy from glucose.

  • Exothermic reaction: A reaction that releases energy in the form of heat and light.

• Energy is transferred, not created, during respiration; energy is converted from chemical energy in glucose to forms usable by the cell, like ATP.

How Organisms Use Energy from Respiration

• Building larger molecules from smaller ones (e.g., amino acids to proteins).

• Muscular contraction for movement facilitated by the conversion of ATP to mechanical energy.

• Maintaining body temperature through metabolic processes that generate heat.

• Active transport: Energy is required to move molecules against their concentration gradient.

• Cell division: Energy is crucial for synthesizing new cellular components.

• Nerve impulse transmission: Maintaining ion gradients requires energy.

• Energy is needed for many reactions in the body; these reactions are often enzyme-catalyzed and require specific conditions.

Types of Respiration

• Aerobic respiration: Occurs when there's enough oxygen; it's the primary energy-releasing pathway in most organisms.

• Anaerobic respiration: Occurs without oxygen; it's less efficient but allows cells to produce some energy in oxygen-deprived conditions.

Aerobic Respiration

• Most efficient way to transfer energy from glucose, yielding a large amount of ATP.

• Takes place continuously in plants and animals in most cells.

• Occurs in mitochondria (sub-cellular structures) which contain enzymes for the Krebs cycle and electron transport chain.

• Word equation: Glucose + Oxygen → Carbon Dioxide + Water

• Chemical equation: C6H12O6 + 6O2 \rightarrow 6CO2 + 6H2O

• The energy released is used to generate ATP (adenosine triphosphate), the main energy currency of the cell.

Anaerobic Respiration

• Respiration without oxygen, primarily used when oxygen is limited or absent.

• Occurs when oxygen supply is insufficient (e.g., during sprinting, or in waterlogged soils).

• In humans, glucose is only partially broken down, leading to less energy and lactic acid production.

• Word equation (humans): Glucose → Lactic Acid

• Inefficient as not all energy from glucose is released compared to aerobic respiration.

• Produces lactic acid, which is toxic and must be removed because it causes muscle fatigue and cramps; it's later converted back to glucose in the liver using oxygen.

Anaerobic Respiration in Plants and Yeast

• Word equation (plants and yeast): Glucose → Ethanol + Carbon Dioxide

• In yeast, this process is called fermentation, a type of anaerobic respiration.

• Industrial applications of fermentation:

  • Bread making: Carbon dioxide creates air pockets, making bread light.

  • Alcohol production (beer and wine): Ethanol is produced by yeast.

• Other applications include the production of biofuels, pharmaceuticals, and certain food products.