AP Biology - Plants and Human Body Systems
OpenStax Biology for AP — Chapter 30: The Respiratory System — AP BIOLOGY Revision Notes & Topical Questions
5 min read 8 parts Lesson 11 of 15 Unit quiz
Lesson summary
OpenStax Biology for AP — Chapter 30: The Respiratory System — AP BIOLOGY notes: Describe the structure of the respiratory system, breathing mechanics, gas transport, control of breathing and gas exchange in other animals.Air is warmed and humidified in the nasal cavity, then pas…
- Inhalation
- Surfactant
- Carbonic anhydrase
- Chloride shift
- Counter-current flow
- Medulla oblongata
Section 1 of 8Structure of the mammalian system
Structure of the mammalian system
Air is warmed and humidified in the nasal cavity, then passes through the pharynx and trachea into the bronchi.
Gas exchange begins in the respiratory bronchioles and occurs in the alveolar ducts, sacs and alveoli.
Hair and mucus trap particles, and cilia move mucus up to be swallowed.
Section 2 of 8The alveolus
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Alveoli are the functional unit of gas exchange.
2
Each is thin (one cell thick), moist and surrounded by capillaries.
- This gives a short diffusion distance, a large surface area and a steep concentration gradient maintained by blood flow and ventilation.
3
Oxygen dissolves in the moisture lining the alveolus, diffuses into the blood and binds haemoglobin; CO2 diffuses the other way.
4
Gas movement follows partial pressure differences.
Section 3 of 8Breathing mechanics
Inhalation
- Inhalation the diaphragm contracts and flattens and the external intercostal muscles raise the ribs.
- Thoracic volume increases and pressure falls, so air flows in.
Exhalation at rest is passive, as the muscles relax and the lungs recoil.
Surfactant, a mixture of phospholipids and lipoproteins, reduces surface tension and keeps alveoli open.
Section 4 of 8Gas transport
Oxygen
- Oxygen haemoglobin has four subunits with iron-containing haem groups, and binding becomes easier as more oxygen binds.
Carbon dioxide travels as bicarbonate, bound to proteins or haemoglobin, or dissolved.
Most CO2 is carried as bicarbonate ions (HCO3−).
- In red blood cells carbonic anhydrase converts CO2 and water to carbonic acid, which dissociates into H+ and HCO3−.
- H+ binds haemoglobin and bicarbonate moves into the plasma in exchange for chloride (the chloride shift).
- In the lungs the reaction reverses and CO2 is exhaled.
Section 5 of 8Control of breathing
Control of breathing
The breathing rate is set by the medulla oblongata.
A rise in CO2 lowers pH, chemoreceptors detect it, and the medulla increases breathing rate and depth.
Oxygen level has a smaller effect in normal conditions.
Section 6 of 8Gas exchange in other animals
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Fish gills use counter-current flow, which maintains a gradient along the whole lamella so a high proportion of oxygen is absorbed.
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Insects use tracheae, tubes that carry air directly to tissues.
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Birds use one-way air flow through air sacs and parabronchi, which is efficient at high altitude.
4
All exchange surfaces are thin, moist, large and well supplied with blood or air.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Alveolus | Thin, moist air sac where gas exchange occurs. |
| Surfactant | Mixture of phospholipids and lipoproteins that reduces surface tension in alveoli. |
| Carbonic anhydrase | Enzyme that converts CO2 and water to carbonic acid. |
| Chloride shift | Exchange of bicarbonate for chloride across the red cell membrane. |
| Counter-current flow | Blood and water flowing in opposite directions across gills. |
| Medulla oblongata | Brainstem centre controlling breathing rate. |
Section 8 of 8Exam technique
1
Saying most CO2 is carried by haemoglobin — most is carried as bicarbonate
2
Saying breathing rate is controlled mainly by blood oxygen — it responds mainly to CO2 and pH
3
Describing alveolar walls as thick to protect them — they are thin for rapid diffusion
4
Forgetting that ventilation maintains the concentration gradient
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