Questions and Answers
Which statement describes all living things?
They are composed of one or more cells.
Based on cell theory, why is a virus considered non-living?
A virus cannot reproduce itself without a host cell.
According to cell theory, what can primitive cells, like prokaryotes, do?
They can carry out the functions of life.
Which statement best describes the process pictured?
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Which is a characteristic of a virus, but NOT a bacterium?
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Viruses have all of the characteristics of living things EXCEPT?
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Why do viruses need living hosts, such as bacteria or eukaryote cells?
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Why is a virus referred to as a particle rather than a cell?
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What part of the cell theory MOST implies that viruses cannot be considered a life form?
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Unlike a prokaryotic bacteria cell, a virus cannot?
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Viral characteristics include all BUT which one?
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According to the passage, the MOST IMPORTANT evidence supporting the opinion that viruses are not alive is that they?
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When scientists classify living things, they do not include viruses because they?
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__________ are found in BOTH viruses AND in living single-celled organisms, such as protozoans and bacteria.
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Viruses attack host cells and cause disease for all EXCEPT which one reason?
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Which feature is NOT used to classify a virus?
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Based on the information provided, what is a major difference between viruses and bacteria?
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Virus? Living or not? If we use the image as an indicator, we might say living because?
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According to cell theory, scientists do not classify a virus as living because it does not have?
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Study Notes
Characteristics of Living Things
- All living things are made up of one or more cells.
- Viruses do not possess cellular structure, classifying them as non-living entities.
Cell Theory and Viruses
- Cell theory posits that even simple cells like prokaryotes perform life functions, while viruses rely on host cells for reproduction.
- Viruses must infect host cells to replicate, highlighting their non-living nature.
Structure of Viruses
- Viruses consist of a nucleic acid core (either DNA or RNA) encased in a protein coat known as a capsid.
- Unlike bacteria, viruses lack a cellular structure and cannot reproduce independently.
Viral Reproduction
- Viruses hijack the reproductive machinery of host cells, directing them to produce viral components.
- They cannot reproduce on their own; they require a living host for metabolic functions.
Classification Challenges
- Viruses are not included in scientific classifications of living organisms due to their lack of cellular composition.
- Classification criteria for viruses do not involve the shape of their nucleus, as they do not possess one.
Evidence of Non-Living Status
- Key evidence supporting the view that viruses are not alive includes their inability to carry out metabolic processes independently.
- Viruses were historically considered alive until the tobacco mosaic virus was crystallized, refuting the idea of them possessing metabolic functions.
Differentiating Viruses and Bacteria
- A critical distinction is that viruses are enveloped in a protein coat while bacteria have a cell wall.
- Viruses, despite containing nucleic acids, depend entirely on host cells for survival and reproduction.
Debate on Viral Life
- Despite some characteristics resembling living organisms, consensus among scientists is that viruses are not alive due to their pathogenic reliance on host cells.
- The ongoing debate about the definition of life makes the classification of viruses a complex issue.
Summary of Viruses
- Viruses exhibit viral characteristics but do not possess nucleic acids, indicating a structural limitation.
- Their interaction with host cells raises fundamental questions about the nature of life and what constitutes living status.
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Test your understanding of cell theory and the characteristics of living organisms with these flashcards. Each card presents a key concept related to cells, including the definition of life and the nature of viruses. Perfect for preparing for biology exams or enhancing your knowledge in life sciences.