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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1:03 minutes

Problem 4

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.

Verified step by step guidance

Understand the concept of countercurrent gas exchange: This is a mechanism in which blood and water flow in opposite directions across the gills of a fish. This arrangement maximizes the efficiency of oxygen diffusion from water into the blood.

Recall the principle of diffusion: Oxygen moves from an area of higher partial pressure to an area of lower partial pressure. In countercurrent exchange, the gradient for oxygen diffusion is maintained along the entire length of the gill lamellae.

Analyze the options: Option (a) suggests that countercurrent exchange maintains a gradient that enhances diffusion. This aligns with the mechanism of countercurrent exchange, as the gradient is preserved due to the opposite flow of water and blood.

Evaluate the other options: Option (b) is incorrect because countercurrent exchange does not depend on whether the fish is swimming or stationary. Option (c) is incorrect because the mechanism does not involve different flow rates but rather opposite flow directions. Option (d) is incorrect because oxygen diffusion occurs along the partial pressure gradient, not against it.

Conclude that the correct answer is the option that aligns with the mechanism of countercurrent gas exchange, which is maintaining a gradient that enhances diffusion.

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Key Concepts

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

Countercurrent Exchange Mechanism

The countercurrent exchange mechanism is a biological process where two fluids flow in opposite directions, maximizing the transfer of substances between them. In fish gills, this mechanism allows oxygen-rich water to flow past oxygen-poor blood, maintaining a concentration gradient that enhances the diffusion of oxygen into the blood.

Diffusion and Partial Pressure

Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. In the context of gas exchange, oxygen moves from water (where its partial pressure is higher) into the blood (where its partial pressure is lower), allowing fish to efficiently extract oxygen even when the water's oxygen levels are low.

Gill Structure and Function

Fish gills are specialized organs designed for gas exchange, consisting of thin filaments and lamellae that increase surface area. This structure facilitates the efficient transfer of oxygen and carbon dioxide between the water and the blood, enabling fish to breathe effectively while submerged.