Biology Quiz: Why Do Viruses Need Living Hosts?

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?

A virus has taken over the reproductive structure of a cell, making it reproduce the virus's RNA. Signup and view all the answers

Which is a characteristic of a virus, but NOT a bacterium?

capsid Signup and view all the answers

Viruses have all of the characteristics of living things EXCEPT?

cells. Signup and view all the answers

Why do viruses need living hosts, such as bacteria or eukaryote cells?

Viruses depend on the host cells that they infect to reproduce. Signup and view all the answers

Why is a virus referred to as a particle rather than a cell?

Structurally, it is an RNA or DNA core surrounded by a protein coat. Signup and view all the answers

What part of the cell theory MOST implies that viruses cannot be considered a life form?

All living things are made of one or more cells. Signup and view all the answers

Unlike a prokaryotic bacteria cell, a virus cannot?

reproduce on its own. Signup and view all the answers

Viral characteristics include all BUT which one?

Viruses do not contain any nucleic acids. Signup and view all the answers

According to the passage, the MOST IMPORTANT evidence supporting the opinion that viruses are not alive is that they?

do not have a cellular structure. Signup and view all the answers

When scientists classify living things, they do not include viruses because they?

are not made of one or more cells. Signup and view all the answers

__________ are found in BOTH viruses AND in living single-celled organisms, such as protozoans and bacteria.

DNA or RNA Signup and view all the answers

Viruses attack host cells and cause disease for all EXCEPT which one reason?

they lack DNA/RNA so they must use the DNA of the host cell. Signup and view all the answers

Which feature is NOT used to classify a virus?

shape of its nucleus. Signup and view all the answers

Based on the information provided, what is a major difference between viruses and bacteria?

Viruses are surrounded by a protein coat; bacteria are surrounded by a cell wall. Signup and view all the answers

Virus? Living or not? If we use the image as an indicator, we might say living because?

it contains a nucleic acid. Signup and view all the answers

According to cell theory, scientists do not classify a virus as living because it does not have?

cellular structure. Signup and view all the answers

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.