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

32. Vertebrates

Chordates

General Biology

32. Vertebrates

Chordates

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0:59 minutes

Problem 2

Textbook Question

In the chordate phylogenetic tree below, fill in the shared derived character that defines each clade.

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Identify the concept of shared derived characters (synapomorphies): These are traits that are unique to a particular clade and are used to define evolutionary relationships within the phylogenetic tree.

Start at the base of the chordate phylogenetic tree. The notochord (a) is the shared derived character that defines all chordates, so it should be placed at the base of the tree.

Move up the tree to the next clade. The vertebral column (b) is the shared derived character that defines vertebrates, so it should be placed at the branch point where vertebrates diverge from other chordates.

Continue to the next clade. Jaws (c) are a shared derived character that defines gnathostomes (jawed vertebrates), so they should be placed at the branch point where jawed vertebrates diverge from jawless vertebrates.

Proceed further up the tree, adding the remaining shared derived characters (d: bony skeleton, e: four limbs, f: amniotic egg, g: hairs) at the appropriate branch points based on their evolutionary appearance. For example, four limbs (e) define tetrapods, and hairs (g) define mammals.

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Key Concepts

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

Notochord

The notochord is a flexible rod-like structure that provides support and defines the primitive axis of the body in chordates. It is a key characteristic of all chordates during some stage of their development, serving as a precursor to the vertebral column in vertebrates. The presence of a notochord is essential for the development of the nervous system and the overall body plan.

Vertebral Column

The vertebral column, or backbone, is a series of vertebrae that encase and protect the spinal cord in vertebrates. It is a defining feature of the subphylum Vertebrata, providing structural support and enabling greater mobility. The evolution of the vertebral column marks a significant advancement in the complexity and functionality of the chordate body plan.

Amniotic Egg

The amniotic egg is a key evolutionary adaptation that allows for reproduction in a terrestrial environment. It features a protective shell and several membranes, including the amnion, which encases the embryo in a fluid-filled cavity. This adaptation is crucial for reptiles, birds, and mammals, as it prevents desiccation and supports the development of the embryo outside of water.