Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

40. Circulatory System

Gas Exchange

General Biology

40. Circulatory System

Gas Exchange

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0:39 minutes

Problem 5

Textbook Question

Explain how each parameter in Fick's law of diffusion is reflected in the structure of the mammalian lung.

Verified step by step guidance

Understand Fick's Law of Diffusion: Fick's Law states that the rate of diffusion (J) across a membrane is proportional to the surface area (A) across which diffusion occurs, the difference in concentration (ΔC) of the substance on either side of the membrane, and inversely proportional to the thickness (Δx) of the membrane. The equation is represented as J = -D (A ΔC / Δx), where D is the diffusion coefficient.

Analyze the Surface Area (A) in Mammalian Lungs: The mammalian lung is structured with numerous alveoli, which are tiny air sacs that greatly increase the surface area available for gas exchange. This extensive surface area aligns with Fick's Law, as a larger surface area (A) facilitates a higher rate of diffusion, allowing efficient oxygen and carbon dioxide exchange.

Examine the Concentration Gradient (ΔC): In the lungs, the concentration gradient is maintained by blood flow on one side of the alveolar membrane and air on the other. Oxygen concentration is higher in the air within the alveoli than in the blood, promoting diffusion of oxygen into the blood. Conversely, carbon dioxide concentration is higher in the blood, promoting its diffusion out into the alveolar air.

Consider the Membrane Thickness (Δx): The alveolar walls in mammalian lungs are extremely thin, minimizing the distance over which diffusion must occur. This thin barrier (Δx) enhances the rate of diffusion according to Fick's Law, as a smaller Δx increases the rate of diffusion.

Reflect on the Diffusion Coefficient (D): While the diffusion coefficient (D) is primarily a property of the diffusing molecule and the medium, in the context of the lungs, factors like temperature and the medium (air or fluid in the alveoli) can affect D. The structure of the lung ensures that conditions are optimal for the diffusion of gases like oxygen and carbon dioxide.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fick's Law of Diffusion

Fick's Law of Diffusion describes the rate at which a substance diffuses across a surface. It states that the diffusion rate is proportional to the concentration gradient, surface area, and permeability of the membrane, while inversely proportional to the thickness of the membrane. This law is fundamental in understanding how gases exchange in biological systems, particularly in the lungs.

Alveolar Structure

The alveoli are tiny air sacs in the lungs where gas exchange occurs. Their large surface area, thin walls, and extensive capillary networks facilitate efficient diffusion of oxygen and carbon dioxide. The structure of the alveoli maximizes the surface area available for gas exchange, aligning with Fick's Law by enhancing the concentration gradient and minimizing diffusion distance.

Concentration Gradient

A concentration gradient refers to the difference in concentration of a substance between two areas. In the lungs, oxygen concentration is higher in the alveoli than in the blood, while carbon dioxide concentration is higher in the blood than in the alveoli. This gradient drives the diffusion of oxygen into the blood and carbon dioxide out of it, illustrating the principles of Fick's Law in action.

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Related Practice

Textbook Question

Which of the following promotes oxygen release from hemoglobin?

a. A decrease in temperature

b. An increase in O₂ level.

c. A decrease in pH

d. A decrease in carbonic anhydrase activity

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Textbook Question

When you hold your breath, which of the following blood gas changes first leads to the urge to breathe?

a. Rising O₂

b. Falling O₂

c. Rising CO₂

d. Falling CO₂

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Textbook Question

Countercurrent gas exchange in the gills of a fish

a. Maintains a gradient that enhances diffusion.

b. Enables the fish to obtain oxygen without swimming.

c. Means that blood and water flow at different rates.

d. Allows O₂ to diffuse against its partial pressure gradient.

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Textbook Question

When you inhale, the diaphragm

a. Relaxes and moves upward.

b. Relaxes and moves downward.

c. Contracts and moves upward.

d. Contracts and moves downward.

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Textbook Question

Frog lungs have a smaller surface area for gas exchange than mammalian lungs. How do frogs compensate for this difference?

a. Frog tissue absorbs more oxygen from the blood than mammalian tissue does.

b. Frogs breathe more quickly than mammals.

c. Frogs also obtain oxygen via diffusion across the skin.

d. Frog lung tissue has a greater density of capillary beds than mammalian lung tissue.

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Textbook Question

Compared with the interstitial fluid that bathes active muscle cells, blood reaching these cells in arterioles has a

a. Higher PO₂.

b. Higher PCO₂.

c. Greater bicarbonate concentration.

d. Lower pH.

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Textbook Question

Carp are fishes that thrive in stagnant-water habitats with low oxygen partial pressure. Compared with the hemoglobin of many other fish species, carp hemoglobin has an extremely high affinity for O₂.

Draw an oxygen–hemoglobin equilibrium curve showing separate lines for carp and a fish that lives in water with a higher oxygen partial pressure.

Explain why they differ.

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Textbook Question

What is the primary feedback used by the brain to control breathing?

a. Heart rate

b. Partial pressure of O₂

c. Blood pH, which indicates O₂ level

d. Blood pH, which indicates CO₂ level

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