Respiration and gas exchange
Respiration and gas exchange
This domain tests aerobic and anaerobic respiration, ATP release, gas exchange surfaces, ventilation in humans and gas exchange in plants.
Core rules
- Aerobic respiration: glucose + oxygen → carbon dioxide + water, releasing energy in usable form. Anaerobic respiration in humans: glucose → lactic acid, releasing less energy. In yeast: glucose → ethanol + carbon dioxide.
- Respiration is a chemical process in cells; breathing is ventilation of the lungs. Do not use them interchangeably.
- Alveoli are efficient because they have a large surface area, thin walls, moist surface, and a good blood supply; ventilation maintains concentration gradients.
- Inhaling: diaphragm contracts and flattens, intercostal muscles raise ribs, volume increases, pressure falls, air enters. Exhaling is the reverse, largely passive at rest.
- Plants exchange gases through stomata in leaves and lenticels in stems. Stomata close to reduce water loss.
Worked example
A person has a tidal volume of 0.5 L and breathes 12 times per minute. Pulmonary ventilation = 0.5 × 12 = 6.0 L/min. Reasoning: this is the volume moved in and out, not the volume reaching the alveoli. Some air remains in the airways as dead space, so alveolar ventilation is lower. If breathing rate doubles but tidal volume halves, ventilation stays the same.
Traps
- Saying anaerobic respiration produces no energy.
- Writing breathing when the question asks about respiration.
- Claiming alveoli have cilia to sweep mucus.
- Saying stomata are for transpiration only.
- Forgetting that plants respire all the time.