3.3 Gaseous Exchange and Respiration

• General characteristics of respiratory surfaces
• Respiratory structures in insects, fish and mammals
• Mechanism of breathing in humans
• Aerobic and anaerobic respiration in animals
• Respiratory quotient

• explain the general characteristics of respiratory surfaces in animals
• describe the structure and adaptations of respiratory structures in animals
• describe the mechanism of gaseous exchange in humans
• describe the process of aerobic and anaerobic respiration
• calculate the respiratory quotient for different foods

“What does every breathing surface have in common, from a fish to a human?”

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1. Respiratory surfaces and breathing
   40 min · 2 practice tasks · quiz
   Four features every gas exchange surface shares, and how humans ventilate theirs.
2. Respiration and the respiratory quotient
   40 min · 2 practice tasks · quiz
   Releasing energy with and without oxygen, and what the gases reveal about the food.
3. Why animals exchange gases
   40 min · 1 practice tasks · quiz
   Breathing moves air; gaseous exchange is diffusion; respiration is the chemistry in cells.
4. Five features every surface must have
   40 min · 1 practice tasks · quiz
   Large, thin, moist, permeable and well supplied: what fails if any one is missing.
5. Body size and specialised organs
   40 min · 1 practice tasks · quiz
   Small animals use the skin. Larger ones need gills, tracheae or lungs because volume outgrows surface.
6. The insect tracheal system
   40 min · 1 practice tasks · quiz
   Spiracles, tracheae and tracheoles take air straight to cells, so insect blood does not carry oxygen.
7. Spiracles, pumping and water loss
   40 min · 1 practice tasks · quiz
   Insects open spiracles to get oxygen and close them to keep water. Fliers can pump the abdomen.
8. Structure of a fish gill
   40 min · 1 practice tasks · quiz
   Operculum, arches, filaments and lamellae turn a small head into a huge, thin, wet surface.
9. Countercurrent flow in gills
   40 min · 1 practice tasks · quiz
   Water and blood run opposite ways so a gradient exists along the whole lamella.
10. Why gills work in water and fail in air
    40 min · 1 practice tasks · quiz
    Lamellae collapse and dry in air. Polluted or hot water can starve a fish of oxygen even while it is wet.
11. Gas exchange in a frog
    40 min · 1 practice tasks · quiz
    Skin, mouth lining and simple lungs share the job. Dry skin shuts the main route.
12. The path of air in a mammal
    40 min · 1 practice tasks · quiz
    Nose, pharynx, larynx, trachea, bronchi and bronchioles clean, warm and deliver air to alveoli.
13. Alveoli as the exchange surface
    40 min · 1 practice tasks · quiz
    Millions of moist, one-cell sacs wrapped in capillaries give a tennis-court of area in the chest.
14. Thorax, pleura and diaphragm
    40 min · 1 practice tasks · quiz
    An airtight box, a slippery pleural seal and a sheet of muscle turn volume changes into air flow.
15. How inspiration works
    40 min · 1 practice tasks · quiz
    Muscles, then volume, then pressure, then flow. Lungs do not suck.
16. Expiration and forced breathing
    40 min · 1 practice tasks · quiz
    Quiet expiration is passive elastic recoil. Forced expiration recruits internal intercostals and abdominals.
17. The bell-jar model of the thorax
    40 min · 1 practice tasks · quiz
    A practical model shows volume pulling air in. Its limits are as important as its success.
18. Lung volumes, rate and exercise
    40 min · 1 practice tasks · quiz
    Tidal volume times rate is ventilation. Exercise raises both; recovery time measures fitness.
19. What controls breathing rate
    40 min · 1 practice tasks · quiz
    The medulla responds mainly to carbon dioxide, not to a lack of oxygen. That is why you cannot hold your breath until you die.
20. How blood carries the gases
    40 min · 1 practice tasks · quiz
    Haemoglobin binds oxygen. Most carbon dioxide travels as hydrogencarbonate in plasma. Carbon monoxide cheats the system.
21. Aerobic respiration in animal cells
    40 min · 1 practice tasks · quiz
    Glucose plus oxygen in mitochondria yields much ATP, carbon dioxide and water. Animals use the ATP for movement, pumps and heat.
22. Lactic acid and oxygen debt
    40 min · 1 practice tasks · quiz
    When oxygen delivery lags, muscle makes lactic acid. Extra oxygen afterwards pays the debt.
23. Smoking and the lungs
    40 min · 1 practice tasks · quiz
    Tar, nicotine and carbon monoxide wreck cilia, alveoli and oxygen transport. The damage is preventable.
24. Breathing, work and health in Kenya
    40 min · 1 practice tasks · quiz
    Altitude, fish, city air, infection and sport all sit on the same gas-exchange biology.