1.3.1 Respiration is a Chemical Process

Cellular respiration

• Cellular respiration is the process of transferring energy from the breakdown of glucose
  • It is a universal chemical process which is continuously occurring in all living cells
  • Every process happening in your body requires energy
• The energy transferred by respiration cannot be immediately or directly used by the cell
  • Energy is stored in the form of a special molecule of called ATP
  • ATP can then be used in cellular processes where energy is required
  • An analogy of ATP is a rechargeable battery which can store potential energy and release it as kinetic energy
    • Once the energy has been depleted the battery can be recharged
• Organisms need energy for:
  • Chemical reactions to build larger molecules from smaller molecules
  • Muscle contraction to allow movement
  • Keeping warm (to maintain a constant temperature suitable for enzyme activity)
• The energy transferred supplies all the energy needed for metabolic processes to occur within cells and organisms as a whole

Uses of the energy released from respiration

• Although most of the energy generated through respiration uses glucose as a substrate, organisms can break down other molecules to be used in respiration
  • Proteins, lipids (fats) and other carbohydrates can all be utilised
• Cellular respiration can either be aerobic (in the presence of oxygen) or anaerobic (in the absence of oxygen)
• Cellular respiration is controlled by enzymes, consequently the rate can be affected by temperature and pH

Aerobic Respiration

• Aerobic respiration requires oxygen
  • It is defined as the chemical reaction in cells that uses oxygen to break down nutrient molecules to release energy
  • Most aerobic respiration takes place in the mitochondria
• Aerobic respiration is the complete breakdown of glucose to release a relatively large amount of energy for use in cell processes and reactions
• Carbon dioxide and water are produced as waste products as well as releasing useful cellular energy

Word equation for aerobic respiration

• This equation can also be shown as a balanced symbol equation
  • One molecule of glucose combines with six molecules of oxygen to produce six molecules of carbon dioxide and six molecules of water

The balanced symbol equation for aerobic respiration

• Cellular respiration is an exothermic reaction as it transfers energy to the environment in the form of heat
  • This is one of the reasons why our bodies heat-up when we exercise
• The heat generated through aerobic respiration can be demonstrated using germinating beans

Practical investigation: demonstrating the production of heat

Apparatus

• Vacuum Flasks
• Thermometer
• Cotton wool
• Germinating seeds
• Dead/boiled seeds

Method

• Set up the flasks as shown in the diagram
  • Flask A with the germinating seeds
  • Flask B with the dead seeds
• Make sure the cotton wool is plugging the top of each flask
• Hold the thermometer in place with the cotton wool
• Invert the flask
• Record the initial temperature
• After 4 days, record the final temperature

Experiment to demonstrate the production of heat by living material during respiration

Results

• The thermometer in the flask with the germinating seeds (Flask B) should show an increase in temperature
• Flask A should remain at room temperature
• This is because the seeds in flask B are respiring and producing heat energy in the process
• This shows that respiration is an exothermic reaction
• The seeds in flask A are not respiring because they are dead, so the temperature remains the same