GCSE Biology Revision "Respiration"

Introduction to Cellular Respiration

• Energy is essential in biology for various functions:

  • Movement

  • Maintaining body temperature in mammals

  • Driving chemical reactions to synthesize/build larger molecules (e.g., proteins made from joining amino acids)

What is Respiration?

• Definition: Respiration is an exothermic reaction that continually occurs in all living cells.

• Purpose: It provides energy necessary for biological functions.

• Photosynthesis is an exothermic reaction: because it releases energy

Types of Respiration

1. Aerobic Respiration

• Definition: Occurs when glucose reacts with oxygen.

• Products: Carbon dioxide (CO2) and water (H2O) are produced, along with energy.

• Word Equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy

• 

• Chemical Symbols:

  • Glucose: C6H12O6

  • Oxygen: O2

  • Carbon Dioxide: CO2

  • Water: H2O

Key Fact:

• Aerobic respiration releases a large amount of energy due to complete oxidation of glucose. (glucose molecule is fully oxidised)

• if oxygen's present, then cells carry out aerobic respiration.

2. Anaerobic Respiration

• Definition: Occurs when there is insufficient oxygen, such as during intense physical activity.

• 1st Situation: Muscle Cells

  • When there is a shortage of oxygen, muscle cells respire anaerobically for energy to contract. In anaerobic respiration in muscles, glucose is converted to lactic acid, and anaerobic respiration does not require any oxygen.

  • Anaerobic respiration releases much less energy than aerobic respiration because in anaerobic respiration, the oxidation of glucose is incomplete

  • Process: Glucose is converted to lactic acid.

  • Equation: Glucose → Lactic Acid + Energy

  • 

  • Key Fact: Releases much less energy than aerobic respiration due to incomplete oxidation of glucose.

• 2nd Situation: Plant Cells and Yeast Cells

  • Process: In these organisms, glucose is converted to ethanol and carbon dioxide.

  • Equation: Glucose → Ethanol + Carbon Dioxide + Energy

  • 

  • Key Fact: No oxygen is needed for this reaction.

Applications of Anaerobic Respiration

• Fermentation:

  • Alcohol: Anaerobic respiration in yeast (fermentation) is used to produce alcohol (ethanol) in beverages such as beer.

    (alcohol in drinks is called ethanol which is produced from fermentation)

  • Bread Making: Carbon dioxide produced by fermentation creates bubbles, causing dough to rise, which is essential for baking bread.

• Key fact: Cells carry out anaerobic respiration when there is insufficient oxygen. Anaerobic repsiration carrys out less energy