B 3.1 gas exchange

1. Why do organisms need gas exchange?

To obtain O₂ for respiration and remove CO₂.

2. Why do large organisms need specialized gas exchange systems?

Small surface area:volume ratio → diffusion too slow.

3. What features must gas exchange surfaces have?

Large surface area, permeability, moisture, thin barrier.

4. How is the O₂ gradient maintained in humans?

Ventilation brings high‑O₂ air into alveoli.

5. How is the CO₂ gradient maintained?

Blood arriving at alveoli has high CO₂ from respiration.

6. Why are capillary networks important?

Continuous blood flow maintains gradients.

7. What increases lung surface area?

Bronchioles → alveoli.

8. Why are alveoli walls thin?

Short diffusion distance.

9. What surrounds alveoli?

Dense capillary networks.

10. What is the function of surfactant?

Reduces surface tension; prevents alveolar collapse.

11. What drives ventilation?

Pressure changes from muscle contraction.

12. What happens during inhalation?

Diaphragm + external intercostals contract → thoracic volume ↑ → pressure ↓ → air in.

13. What happens during exhalation?

Diaphragm relaxes; internal intercostals + abdominal muscles contract → pressure ↑ → air out.

14. How do ventilation muscles work?

Antagonistically.

15. What is tidal volume?

Air inhaled/exhaled in normal breath.

16. What is vital capacity?

Max air inhaled/exhaled after deepest breath.

17. What is inspiratory reserve volume?

Extra air inhaled after normal inspiration.

18. What is expiratory reserve volume?

Extra air exhaled after normal expiration.

19. What covers the leaf epidermis?

Waxy cuticle → reduces water loss.

20. What regulates stomatal opening?

Guard cells.

21. When do stomata close?

Low water conditions or at night.

22. What do leaf veins contain?

Xylem → supplies water.

23. What is the function of spongy mesophyll?

Air spaces for gas diffusion.

24. What is transpiration?

Loss of water vapor from leaves.

25. Why does transpiration occur?

Humidity inside leaf > outside → diffusion out.

26. How does temperature affect transpiration?

Higher temperature → higher transpiration.

27. How does humidity affect transpiration?

Higher humidity → lower transpiration.

28. How do you calculate stomatal density?

Stomata count ÷ area of field of view (mm²).

29. What is hemoglobin?

Quaternary protein in RBCs that carries oxygen.

30. How many heme groups does hemoglobin have?

Four.

31. What is cooperative binding?

Binding of one O₂ increases affinity for next O₂.

32. What is the Bohr effect?

CO₂ lowers pH → hemoglobin affinity for O₂ decreases.

33. What is carbaminohemoglobin?

CO₂ bound to hemoglobin.

34. Why is reduced affinity useful?

Promotes O₂ release in active tissues.

35. How does fetal hemoglobin differ?

Higher O₂ affinity.

36. Why does fetal hemoglobin have higher affinity?

Structural differences → allows O₂ uptake from maternal blood.

37. What shape is the hemoglobin dissociation curve?

Sigmoid (S‑shaped).

38. Why is the curve sigmoid?

Cooperative binding.

39. What does a left shift indicate?

Higher O₂ affinity (e.g., fetal hemoglobin).