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
- 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 6m
- 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 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
- 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 49m
- 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
24. History of Life on Earth
History of Life on Earth
Problem 1
Textbook Question
How many different species have been identified by science?
How many are estimated to exist?

1
Understand the context of the question: The problem is asking about the number of species identified by science and the estimated total number of species that exist. This involves concepts in biodiversity and taxonomy.
Step 1: Explain the term 'identified species': These are species that have been formally described and named by scientists, following the rules of taxonomy. This includes organisms across all domains of life, such as animals, plants, fungi, and microorganisms.
Step 2: Discuss the estimated number of species: Scientists use various methods, such as sampling and extrapolation, to estimate the total number of species on Earth. This includes species that have not yet been discovered or described.
Step 3: Highlight the disparity between identified and estimated species: While millions of species have been identified, the estimated number of species is much higher, indicating that a significant portion of Earth's biodiversity remains unexplored.
Step 4: Provide examples of why many species remain unidentified: Factors include inaccessible habitats (e.g., deep oceans, dense rainforests), microscopic organisms, and the rapid rate of extinction before discovery.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Biodiversity
Biodiversity refers to the variety of life forms on Earth, encompassing the diversity of species, ecosystems, and genetic variations within species. It is crucial for ecosystem stability and resilience, providing essential services such as pollination, nutrient cycling, and climate regulation. Understanding biodiversity helps scientists assess the health of ecosystems and the impact of human activities on the environment.
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Species Identification
Species identification is the process of recognizing and classifying organisms based on their characteristics and genetic makeup. Scientists use various methods, including morphological analysis and genetic sequencing, to identify and categorize species. Accurate identification is essential for understanding biodiversity and monitoring changes in species populations over time.
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Estimates of Species Richness
Estimates of species richness refer to the predicted number of species that exist in a particular area or globally, based on scientific research and statistical models. While approximately 1.5 million species have been formally described, estimates suggest that the total number could range from 5 to 30 million species, highlighting the vast unknown diversity on Earth. These estimates are important for conservation efforts and understanding ecological dynamics.
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Related Practice
Multiple Choice
If the feathers of extant flying birds originally arose as thermoregulatory devices in ancestral reptiles, then flight feathers could be accurately described as __________.
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