Chapter summary
Respiration in humans, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Follow air into the lungs
Which structures move air, and where do gases actually cross into blood?
Key idea and reminders
Airways conduct air to alveoli; the closely associated capillaries carry blood past the exchange surface.
- Larynx -> trachea -> bronchi -> bronchioles -> alveoli.
- Alveoli exchange gases with blood in adjacent capillaries.
- Ventilation, gas exchange and cellular respiration are different processes.
Keep in mind: Air travels through bronchioles to alveoli. Capillaries carry blood beside the alveoli.
02
Exchange gases at an alveolus
How do very small air spaces provide fast gas exchange?
Key idea and reminders
A large total surface area, thin moist walls and maintained gradients make alveoli effective exchange surfaces.
- Oxygen diffuses from alveolar air into blood; carbon dioxide diffuses from blood into alveolar air.
- Thin alveolar and capillary walls shorten diffusion distance.
- Ventilation and blood flow help maintain concentration gradients.
Keep in mind: Thin alveolar and capillary walls permit rapid diffusion of dissolved gases. Blood and alveolar air remain in separate spaces.
03
Link smoke components to effects
Why do nicotine, tar and carbon monoxide need different explanations?
Key idea and reminders
Nicotine affects dependence and circulation; tar damages airways; carbon monoxide reduces oxygen carriage.
- Nicotine is addictive and can increase heart rate and blood pressure.
- Tar contains carcinogens and can damage cilia and lung tissue.
- Carbon monoxide binds haemoglobin, reducing its capacity to carry oxygen.
Keep in mind: They have different targets. Explain nicotine through dependence and circulation, tar through airway and tissue damage, and carbon monoxide through haemoglobin binding.
04
Aerobic respiration releases energy
What changes during aerobic respiration, and where does the energy come from?
Key idea and reminders
Aerobic respiration breaks down glucose using oxygen, releasing energy and producing carbon dioxide and water.
- Glucose + oxygen -> carbon dioxide + water; energy is released.
- Respiration occurs in living cells, including at rest.
- Breathing supplies gases; it is not the chemical breakdown of glucose.
Keep in mind: The lungs exchange gases. Many body cells use oxygen to respire; for example, muscle cells release energy for contraction.
05
Anaerobic respiration and recovery
Why can rapid, deep breathing continue after a sprint ends?
Key idea and reminders
When oxygen delivery cannot meet intense demand, anaerobic respiration contributes energy; recovery requires extra oxygen.
- Human anaerobic word equation: glucose -> lactic acid, with energy released.
- Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.
- Rapid, deep breathing after exercise supplies additional oxygen for recovery and removal of the oxygen debt.
Keep in mind: Aerobic respiration can continue. Anaerobic respiration supplies an additional contribution when oxygen delivery cannot meet the full demand.