• The Features of Gas Exchange Surfaces in Humans:
  • A large surface area which allows for the diffusion of gases
  • The walls of the alveolus is thin and allows gases diffuse across them quickly
  • They are moist to prevent the cells from drying and to allow gases to dissolve
  • They have a high concentration gradient which is maintained by the movement of air and blood

The Functions of the Cartilage in the Trachea

• To connect bones together
• To provide smooth surfaces enabling tissue to slide easily
• Epiglottis closes the trachea and stops food from going down the trachea when you swallow
• It allows ribs to swing up and down

The Role of Ribs, the Internal, and External Intercostal Muscles, and the Diaphragm in Producing Volume and Pressure Changes in the Thorax Leading to the Ventilation of the Lungs

• Breathing In:
  • External intercostal muscles contract
  • Internal intercostal muscles relax
  • Ribs lift upwards
  • Diaphragm contracts and flattens
  • Volume of thorax increases
  • Pressure in thorax decreases
  • Air flows in; down a pressure gradient
• Breathing Out:
  • External intercostal muscles relax
  • Internal intercotal muscles contract
  • Ribs fall in
  • Diaphragm relaxes and goes back into its domed shape

The Differences in Composition between Inspired and Expired Air

Limewater as a Test for Carbon-dioxide to Investigate the Differences in Composition between Inspired and Expired Air

• Apparatus Needed:
  • Rubber tubing
  • Test tube
• Experiment
  • Sterilize the rubber tubing
  • Do not blow or suck hard when doing the experiment, breathe in and out gently using the rubber tubing
  • Use either limewater or hydrogenocarbonate indicator solution
  • Limewater changes from clear to cloudy when CO₂ dissolves in it and hydrogenocarbonate changes from red to yellow

The Link between Physical Activity and Rate and Depth of Breathing in Terms of the Increased Carbon-dioxide Concentration in the Blood Detected by the Brain, Causing an Increased Rate of Breathing

• Tidal Volume: Amount of air during normal, relaxed breathing
• Vital Capacity: Maximum amount of air breathed in or out in one breath
• During normal breathing:
  • Depth (tidal volume): Approximately 0.5 L
  • Rate: 12 breaths/minute
• During exercise:
  • Depth (tidal volume): Approximately 5 L (depending on sex, age, size, and fitness of the person)
  • Rate: Over 20 breaths/minute

Link between Physical Activity and Rate of Depth of Breathing

• When someone is doing exercise, like running, the muscles use up a  lot of energy and the muscles need a lot of oxygen very quickly
• Breathing becomes faster and deeper to get more oxygen into the muscles quickly as possible and so the concentration of CO₂ in the blood increases
• At a point, the limit is reached and the heart and lungs cannot supply oxygen to the muscles any faster, therefore a little extra energy is produces by anaerobic respiration. Anaerobic respiration produces lactic acid, so the concentration of lactic acid in the blood goes up and the blood pH reduces
• The brain senses these changes and nerve impulses are sent to the diaphragm and intercostal muscles, stimulating them to contract harder and more often

The Role of Goblet Cells, Mucus, and Ciliated Cells in Protecting the Gas Exchange System from Pathogens and Particles

• Goblet cells produce mucus which traps dirt and particles
• Cilia beats to move fluid out of the airway reducing the risk of pathogens entering the lungs
• Mucus also protects the lining