Q1. Differentiate a virus from a bacterium.

Background

Topic: Viruses vs. Bacteria

This question tests your understanding of the fundamental differences between viruses and bacteria, including their structure, replication, and classification.

Key Terms:

• Virus: A non-cellular infectious agent that requires a host cell to replicate.

• Bacterium: A unicellular, prokaryotic microorganism capable of independent life and reproduction.

Step-by-Step Guidance

1. Consider the structural differences: Viruses lack cellular structure (no cytoplasm, organelles, or plasma membrane), while bacteria are cells with these features.

2. Think about replication: Viruses require a host cell to reproduce, but bacteria can reproduce independently by binary fission.

3. Reflect on genetic material: Viruses may have DNA or RNA, but bacteria always have both DNA and RNA.

4. Consider size and visibility: Viruses are much smaller than bacteria and typically require electron microscopy to be seen.

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Q2. How could the small size of viruses have helped researchers detect viruses before the invention of the electron microscope?

Background

Topic: Discovery of Viruses

This question explores how the physical properties of viruses contributed to their early detection, even before advanced imaging technology was available.

Key Terms:

• Filtration: The process of passing a solution through a filter to separate particles by size.

• Electron Microscope: A tool that allows visualization of structures much smaller than those visible with light microscopes.

Step-by-Step Guidance

1. Recall that viruses are smaller than bacteria and can pass through filters that retain bacteria.

2. Think about early experiments where infectious agents passed through filters, suggesting the presence of something smaller than bacteria.

3. Consider how this property led researchers to hypothesize the existence of viruses before they could be directly observed.

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Q3. Describe the chemical and physical structure of both an enveloped and a nonenveloped virus.

Background

Topic: Viral Structure

This question tests your knowledge of the basic components of viruses and the differences between enveloped and nonenveloped forms.

Key Terms:

• Capsid: Protein coat surrounding the viral genome.

• Envelope: Lipid membrane derived from the host cell, present in some viruses.

• Spikes: Glycoprotein projections involved in host cell attachment.

Step-by-Step Guidance

1. Identify the core components: All viruses have a nucleic acid genome (DNA or RNA) and a protein capsid.

2. For enveloped viruses, describe the presence of a lipid envelope surrounding the capsid, often with embedded spikes.

3. For nonenveloped viruses, note the absence of an envelope; the capsid is the outermost layer.

4. Consider the functional implications: Envelopes aid in entry into host cells, while nonenveloped viruses are generally more resistant to environmental stress.

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Q4. Diagram a nonenveloped polyhedral virus that has spikes.

Background

Topic: Viral Morphology

This question asks you to visualize and represent the structure of a specific type of virus.

Key Terms:

• Polyhedral Virus: A virus with a many-sided (often icosahedral) capsid shape.

• Spikes: Surface proteins that protrude from the capsid and facilitate attachment to host cells.

Step-by-Step Guidance

1. Draw a geometric shape (such as an icosahedron) to represent the polyhedral capsid.

2. Indicate the presence of spikes by adding projections extending from the capsid surface.

3. Label the capsid, spikes, and the location of the viral genome inside the capsid.

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Q5. Define viral species. How does a virus species differ from a bacterial species?

Background

Topic: Viral Taxonomy

This question examines your understanding of how viruses are classified and how this differs from bacterial classification.

Key Terms:

• Viral Species: A group of viruses sharing the same genetic information and ecological niche.

• Bacterial Species: A group of bacteria with similar characteristics that can reproduce by binary fission.

Step-by-Step Guidance

1. Define what constitutes a viral species, focusing on genetic similarity and ecological niche.

2. Contrast this with the definition of a bacterial species, which is based on phenotypic and genetic similarity and reproductive capability.

3. Consider why viruses cannot be classified by reproduction in the same way as bacteria.

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