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
14. DNA Synthesis2h 27m
15. Gene Expression3h 12m
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

1. Introduction to Biology

Introduction to Taxonomy

General Biology

1. Introduction to Biology

Introduction to Taxonomy

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Multiple Choice

How could a biologist distinguish an acoel flatworm from a free-living platyhelminth?

Acoel flatworms have a segmented body, whereas free-living platyhelminths are unsegmented.

Acoel flatworms have a complete digestive tract, but free-living platyhelminths do not.

Acoel flatworms possess a coelom, while free-living platyhelminths are acoelomate.

Acoel flatworms lack a true gut cavity, while free-living platyhelminths possess a branched gastrovascular cavity.

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Verified step by step guidance

Step 1: Understand the key anatomical differences between acoel flatworms and free-living platyhelminths. Acoel flatworms lack a true gut cavity, meaning they do not have a specialized structure for digestion. Free-living platyhelminths, on the other hand, possess a branched gastrovascular cavity, which serves as their digestive system.

Step 2: Recognize that the presence or absence of a gut cavity is a defining characteristic. Acoel flatworms rely on intracellular digestion, where food is digested within individual cells, while free-living platyhelminths use their branched gastrovascular cavity for extracellular digestion.

Step 3: Eliminate the incorrect options based on anatomical features. For example, acoel flatworms are unsegmented, just like free-living platyhelminths, so segmentation is not a distinguishing factor. Similarly, neither group has a coelom, as both are acoelomate organisms.

Step 4: Note that acoel flatworms do not have a complete digestive tract. Instead, they absorb nutrients directly into their cells, whereas free-living platyhelminths use their branched gastrovascular cavity to distribute nutrients throughout their body.

Step 5: Conclude that the correct distinguishing feature is the lack of a true gut cavity in acoel flatworms compared to the branched gastrovascular cavity in free-living platyhelminths. This difference is critical for identifying and classifying these organisms.