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 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 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
17. Viruses
Viruses
Problem 9
Textbook Question
Which of the following is/are always true?
a. Viruses cannot reproduce outside a host cell
b. Viruses are not surrounded by a membrane
c. Viruses are not made up of cells
d. A and C are correct
e. A, B, and C are correct

1
Step 1: Understand the nature of viruses. Viruses are acellular entities, meaning they are not made up of cells. This is a fundamental characteristic that distinguishes them from living organisms like bacteria, plants, and animals.
Step 2: Analyze the statement in option (a). Viruses cannot reproduce on their own and require a host cell to replicate. This is because they lack the cellular machinery (e.g., ribosomes, enzymes) necessary for independent reproduction.
Step 3: Evaluate the statement in option (b). Viruses are not surrounded by a membrane. Instead, they are typically composed of a protein coat (capsid) that encloses their genetic material, and some viruses may have an additional lipid envelope derived from the host cell membrane.
Step 4: Combine the information from steps 1, 2, and 3 to assess option (d). Option (d) states that both (a) and (c) are correct. Since both statements are true, this option is valid.
Step 5: Assess option (e), which claims that (a), (b), and (c) are all correct. Since all three statements are consistent with the characteristics of viruses, this option is also valid. Compare this with the other options to determine the most comprehensive answer.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Virus Reproduction
Viruses are unique biological entities that cannot reproduce independently; they require a host cell to replicate. Once inside a host, they hijack the cellular machinery to produce new viral particles, which is essential for their life cycle. This characteristic distinguishes them from living organisms, which can reproduce on their own.
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Viral Structure
Viruses are composed of genetic material (either DNA or RNA) encased in a protein coat called a capsid. Unlike cells, they lack a cellular structure and are not surrounded by a membrane. This structural simplicity is a key feature that defines viruses and differentiates them from cellular life forms.
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Cell Theory
Cell theory is a fundamental principle in biology stating that all living organisms are composed of cells, which are the basic units of life. Viruses do not fit this definition as they are acellular and do not possess the characteristics of living cells, such as metabolism or cellular organization. This distinction is crucial for understanding the nature of viruses.
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