Table of contents
- 1. Introduction to Biology2h 42m
- 2. Chemistry3h 40m
- 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
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses19m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 20m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport1h 2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System1h 10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System1h 4m
- 44. Animal Reproduction1h 2m
- 45. Nervous System1h 55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
32. Vertebrates
Chordates
Problem 6`
Textbook Question
Which of the following could be considered the most recent common ancestor of living tetrapods?
a. A sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates
b. An armored, jawed placoderm with two pairs of appendages
c. An early ray-finned fish that developed bony skeletal supports in its paired fins
d. A salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes

1
Understand the concept of tetrapods: Tetrapods are vertebrates with four limbs, including amphibians, reptiles, birds, and mammals. They evolved from lobe-finned fishes.
Identify key evolutionary traits: The transition from aquatic to terrestrial life involved the development of limbs with skeletal supports that could bear weight on land.
Analyze option a: A sturdy-finned, shallow-water lobe-fin with appendages having skeletal supports similar to terrestrial vertebrates suggests a transitional form between aquatic and terrestrial life.
Consider the evolutionary timeline: Lobe-finned fishes are known to be ancestors of tetrapods, as they possess limb-like structures that could evolve into legs.
Evaluate the other options: Options b, c, and d describe organisms that either do not fit the evolutionary timeline or lack the necessary adaptations for terrestrial life, such as the armored placoderm or the ray-finned fish.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Tetrapods
Tetrapods are vertebrates with four limbs, including amphibians, reptiles, birds, and mammals. They evolved from lobe-finned fishes during the Devonian period, adapting to life on land. Understanding tetrapods involves studying their evolutionary transition from aquatic to terrestrial environments, which is marked by changes in limb structure and function.
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Tetrapods
Lobe-finned Fish
Lobe-finned fish, or Sarcopterygii, are characterized by fleshy, lobed, paired fins, which are supported by a single bone. These fish are crucial in the study of vertebrate evolution as they are believed to be the ancestors of tetrapods. Their fin structure provided the basis for the development of limbs in terrestrial vertebrates, making them a key focus in understanding the transition from water to land.
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Bony Fish
Common Ancestor
A common ancestor in evolutionary biology refers to an organism from which two or more species have evolved. Identifying the most recent common ancestor of tetrapods involves examining fossil records and morphological traits that link modern tetrapods to their aquatic predecessors. This concept is essential for tracing evolutionary pathways and understanding the shared characteristics among diverse species.
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