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GCSE Biology Revision

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GCSE Biology revision

Aerobic and anaerobic respiration

Respiration

AQA 4.1.1.1
Your specification

AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify and describe What is Cellular Respiration?, How Organisms Use Energy from Respiration and Aerobic Respiration in the context of aerobic and anaerobic respiration.

MOST 🎯🎯

Explain the relationships between What is Cellular Respiration?, How Organisms Use Energy from Respiration and Aerobic Respiration and how they contribute to aerobic and anaerobic respiration.

SOME 🎯🎯🎯

Apply and analyse knowledge of What is Cellular Respiration?, How Organisms Use Energy from Respiration and Aerobic Respiration to interpret unfamiliar information about aerobic and anaerobic respiration.

Revision summary

Key knowledge

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What is Cellular Respiration?

  • Cellular respiration is an exothermic reaction that transfers energy from glucose and continuously occurs in living cells
  • Energy is released (transferred) from glucose molecules — it is never created, only transferred
  • Respiration takes place in all living cells at all times to meet the body's energy demands

How Organisms Use Energy from Respiration

  • Energy is used to build larger molecules from smaller ones, such as combining amino acids to form proteins
  • Energy is required for muscular contraction, allowing organisms to move their limbs
  • Energy is used to maintain body temperature, keeping organisms warm even in colder environments

Aerobic Respiration

  • Aerobic respiration occurs when there is sufficient oxygen available and is by far the most efficient way to transfer energy from glucose
  • It takes place continuously in both plants and animals within subcellular structures called mitochondria
  • The word equation is: glucose + oxygen → carbon dioxide + water
  • The chemical equation is: C6 H12 O6 + 6O2 → 6CO2 + 6H2 O ​ ​ ​ ​ ​ ​

Anaerobic Respiration in Humans

  • Anaerobic respiration occurs without oxygen and is used when oxygen supply cannot meet the body's demands, such as during sprinting
  • The word equation in humans is: glucose → lactic acid
  • Anaerobic respiration is inefficient because glucose is only partially broken down, releasing less energy than aerobic respiration
  • Lactic acid is a toxic by-product that must be removed from the body after anaerobic respiration occurs

Anaerobic Respiration in Plants and Yeast

  • In plants and yeast, anaerobic respiration follows a different pathway: glucose → ethanol + carbon dioxide
  • In yeast, this process is specifically called fermentation
  • The carbon dioxide produced during fermentation causes bread to rise, creating a light and fluffy texture
  • The ethanol (alcohol) produced by yeast fermentation is exploited in the brewing industry to make beer and wine

Comparing Aerobic and Anaerobic Respiration

  • Aerobic respiration is more efficient as it fully breaks down glucose using oxygen, releasing more energy
  • Anaerobic respiration is less efficient as glucose is only partially broken down and no oxygen is used
  • The products differ: aerobic respiration produces carbon dioxide and water, whereas anaerobic respiration in humans produces lactic acid, and in yeast produces ethanol and carbon dioxide