Biology Study Guide: Viruses, Plant Evolution, and Fungi

Q1. What are some defenses that bacteria have against the viruses that infect them?

Background

Topic: Bacterial Immune Defenses Against Phages

This question tests your understanding of how bacteria protect themselves from viral infections, specifically bacteriophages (viruses that infect bacteria).

Key Terms and Concepts:

• CRISPR-Cas system: A bacterial adaptive immune system that recognizes and cuts foreign DNA.

• Restriction enzymes: Enzymes that cut DNA at specific sequences, targeting foreign DNA.

• Surface protein mutations: Changes in bacterial surface proteins that prevent phage attachment.

Step-by-Step Guidance

1. Recall that bacteriophages infect bacteria by attaching to specific receptors on the bacterial surface and injecting their genetic material.

2. Think about how bacteria can prevent phages from attaching—consider mutations in surface proteins that act as receptors.

3. Consider how bacteria can destroy foreign DNA once it enters the cell—restriction enzymes play a role here.

4. Remember that some bacteria have an adaptive immune system (CRISPR-Cas) that can recognize and cut viral DNA based on previous infections.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria defend against phages using the CRISPR-Cas system (which recognizes and cuts viral DNA), restriction enzymes (which cut foreign DNA), and by evolving surface proteins that phages can no longer recognize as receptors.

Q2. What is the host range for viruses and what determines the host range?

Background

Topic: Viral Host Range

This question is about the specificity of viruses for infecting certain species or cell types, and what molecular interactions determine this specificity.

Key Terms and Concepts:

• Host range: The spectrum of host species or cell types a virus can infect.

• Receptor binding: The interaction between viral surface proteins and host cell receptors.

• Narrow vs. broad host range: Some viruses infect only one species (narrow), others infect multiple species (broad).

Step-by-Step Guidance

1. Define what is meant by 'host range' in the context of viruses.

2. Think about what determines whether a virus can infect a particular cell or organism—focus on molecular interactions.

3. Consider examples of viruses with narrow and broad host ranges.

4. Explain how the presence or absence of specific receptors on host cells influences host range.

Try solving on your own before revealing the answer!

Final Answer:

The host range is the limited set of species or cell types a virus can infect, determined by the ability of viral surface proteins to bind to specific receptors on host cells. Some viruses have a narrow host range (e.g., only one species), while others have a broad host range (e.g., multiple species).

Q3. Explain the difference between the Lytic and Lysogenic replicative cycles.

Background

Topic: Viral Replication Strategies in Bacteriophages

This question tests your understanding of the two main cycles by which bacteriophages replicate within bacterial cells.

Key Terms and Concepts:

• Lytic cycle: Viral replication that results in the destruction (lysis) of the host cell.

• Lysogenic cycle: Viral DNA integrates into the host genome and replicates without killing the host immediately.

• Prophage: Viral DNA that is integrated into the host genome during the lysogenic cycle.

Step-by-Step Guidance

1. Describe the sequence of events in the lytic cycle, focusing on infection, replication, assembly, and cell lysis.

2. Describe the sequence of events in the lysogenic cycle, focusing on integration of viral DNA and replication with the host genome.

3. Compare the outcomes for the host cell in each cycle.

4. Explain how a virus can switch from the lysogenic to the lytic cycle under certain conditions.

Try solving on your own before revealing the answer!

Final Answer:

The lytic cycle results in the production of new phages and the lysis (death) of the host cell, while the lysogenic cycle involves integration of the viral genome into the host's DNA, allowing the virus to replicate without killing the host immediately.

Q4. What challenges did early land plants face when adapting to life on land? What adaptations allowed them to thrive?

Background

Topic: Plant Evolution and Adaptations to Terrestrial Life

This question explores the evolutionary challenges faced by the first land plants and the adaptations that enabled their survival and success.

Key Terms and Concepts:

• Desiccation: Drying out due to exposure to air.

• Cuticle: Waxy layer that prevents water loss.

• Stomata: Pores for gas exchange.

• Lignin: Structural polymer for support.

• Vascular tissue (xylem and phloem): Transport of water, nutrients, and sugars.

Step-by-Step Guidance

1. List the main environmental challenges faced by early land plants (e.g., water loss, support, nutrient acquisition, reproduction).

2. For each challenge, identify the adaptation that addressed it (e.g., cuticle for water loss, lignin for support).

3. Explain how stomata balance the need for gas exchange with water conservation.

4. Discuss the role of vascular tissues in transporting water and nutrients.

Try solving on your own before revealing the answer!

Final Answer:

Early land plants faced challenges such as desiccation, structural support, nutrient acquisition, and reproduction without water. Adaptations included a waxy cuticle, stomata, lignin for support, vascular tissues, and new reproductive strategies.

Q5. Name the four key traits that appear in nearly all plants (these are absent in charophytes, plants' closest algal relatives).

Background

Topic: Derived Traits of Land Plants

This question focuses on the unique features that distinguish land plants from their closest algal relatives.

Key Terms and Concepts:

• Alternation of generations: Life cycle with multicellular haploid and diploid stages.

• Multicellular, dependent embryos: Embryos retained and nourished by the parent plant.

• Walled spores in sporangia: Protective structures for spore formation.

• Apical meristems: Regions of cell division at plant tips for growth.

Step-by-Step Guidance

1. Recall the main differences between land plants and charophytes.

2. List the four key derived traits found in nearly all land plants.

3. Briefly describe the function or significance of each trait.

4. Consider why these traits were important for terrestrial adaptation.

Try solving on your own before revealing the answer!

Final Answer:

The four key traits are: alternation of generations, multicellular dependent embryos, walled spores produced in sporangia, and apical meristems. These features are absent in charophytes.

Q6. What evidence indicates that charophytes are the closest algal relatives of plants?

Background

Topic: Evolutionary Relationships Between Plants and Algae

This question asks you to identify the shared characteristics that link charophytes and land plants.

Key Terms and Concepts:

• Chlorophyll a and b: Pigments used in photosynthesis.

• Cellulose cell walls: Structural component of plant and charophyte cells.

• Cellulose-synthesizing complexes: Protein rings in the plasma membrane.

• Flagellated sperm: Motile reproductive cells.

• DNA sequence similarity: Genetic evidence of close relationship.

Step-by-Step Guidance

1. List the structural and biochemical similarities between charophytes and land plants.

2. Consider the significance of shared pigments and cell wall composition.

3. Think about the arrangement of cellulose-synthesizing proteins in both groups.

4. Include genetic evidence (DNA sequence similarities) supporting their close relationship.

Try solving on your own before revealing the answer!

Final Answer:

Evidence includes shared chlorophyll types, cellulose cell walls, cellulose-synthesizing protein rings, flagellated sperm, and similar DNA sequences in nuclear, chloroplast, and mitochondrial genomes.

Q7. The haploid gametophyte produces haploid gametes by mitosis and the diploid sporophyte produces haploid spores by meiosis.

Background

Topic: Plant Life Cycle (Alternation of Generations)

This statement is about the alternation of generations in plants, focusing on how gametes and spores are produced.

Key Terms and Concepts:

• Gametophyte: Haploid generation that produces gametes by mitosis.

• Sporophyte: Diploid generation that produces spores by meiosis.

• Mitosis: Cell division that maintains chromosome number.

• Meiosis: Cell division that halves chromosome number.

Step-by-Step Guidance

1. Identify which plant generation is haploid and which is diploid.

2. Recall the type of cell division used by each generation to produce its reproductive cells.

3. Explain why gametophytes use mitosis and sporophytes use meiosis.

4. Connect this process to the alternation of generations life cycle.

Try explaining this process in your own words before checking the answer!

Final Answer:

The gametophyte (haploid) produces gametes by mitosis, while the sporophyte (diploid) produces haploid spores by meiosis, illustrating the alternation of generations in plants.

Q8. Describe characteristics and provide examples of nonvascular plants, seedless vascular plants, and seed plants.

Background

Topic: Major Plant Groups and Their Features

This question asks you to compare the main groups of land plants and give examples of each.

Key Terms and Concepts:

• Nonvascular plants (bryophytes): Lack vascular tissue, gametophyte dominant.

• Seedless vascular plants: Have vascular tissue, do not produce seeds, sporophyte dominant.

• Seed plants: Have vascular tissue and produce seeds.

Step-by-Step Guidance

1. List the defining characteristics of nonvascular plants and provide examples.

2. Describe the features of seedless vascular plants and give examples.

3. Summarize the main traits of seed plants and mention examples.

4. Compare the dominance of gametophyte vs. sporophyte in each group.

Try organizing your answer before revealing the examples!

Final Answer:

Nonvascular plants (e.g., mosses) lack vascular tissue and are gametophyte dominant. Seedless vascular plants (e.g., ferns) have vascular tissue but no seeds and are sporophyte dominant. Seed plants (e.g., flowering plants, conifers) have vascular tissue and produce seeds.

Q9. How did fungi help early plants colonize land?

Background

Topic: Plant-Fungi Symbiosis (Mycorrhizae)

This question explores the mutualistic relationship between fungi and early land plants and its importance for terrestrial colonization.

Key Terms and Concepts:

• Mycorrhizae: Symbiotic association between plant roots and fungi.

• Mutualism: Both organisms benefit from the relationship.

• Water and mineral absorption: Fungi enhance plant uptake of nutrients.

• Pathogen protection: Fungi can help protect plants from soil pathogens.

Step-by-Step Guidance

1. Define mycorrhizae and explain the nature of the plant-fungi relationship.

2. Describe how fungi assist plants in absorbing water and minerals from the soil.

3. Explain how this relationship could have helped early plants survive in terrestrial environments.

4. Mention any additional benefits, such as protection from pathogens.

Try summarizing the role of fungi before checking the answer!

Final Answer:

Fungi formed mutualistic relationships (mycorrhizae) with early plants, helping them absorb water and minerals and providing protection from soil pathogens, which facilitated plant colonization of land.