FUNAL STRUCTURES
\What is the name of the network of branching filaments that makes up the vegetative body of most multicellular fungi?
Mycelium.
A mycelium is composed of branching filaments called hyphae.
What are the two general modes of reproduction found in fungi?
Sexual and asexual reproduction.
Fungi can reproduce through asexual processes and, in many groups, sexual cycles involving nuclear fusion and meiosis.
What is the protein coat that surrounds a virus's genetic material called?
Capsid.
The capsid protects the viral genome.
Why must viruses infect living host cells to reproduce?
They lack the cellular machinery necessary to replicate independently.
Viruses depend on host cells for resources such as ribosomes and metabolic energy.
A scientist observes an organism with branching hyphae and cell walls containing chitin. Which kingdom does it belong to?
Fungi.
Hyphae and chitin-containing cell walls are characteristic fungal traits.
What are the two main types of fungal hyphae, distinguished by whether they contain cross-walls?
Septate and coenocytic hyphae.
Septate hyphae contain septa (cross-walls); coenocytic hyphae lack regular septa and contain multiple nuclei in continuous cytoplasm
What is the term for the fusion of the cytoplasm of two compatible fungal cells during sexual reproduction?
Plasmogamy.
Plasmogamy joins cytoplasm without necessarily joining the nuclei immediately.
What are the protein subunits that make up a viral capsid called?
Capsomeres.
Capsomeres assemble to form the capsid.
What is the name of the viral reproductive cycle that ends with the host cell breaking open and releasing new viruses?
Lytic cycle.
Lysis releases newly produced viral particles.
A virus has an RNA genome enclosed in a protein coat. Does this mean it must also have a membrane envelope?
No.
Viruses may have RNA genomes with or without a membranous envelope.
A fungal cell wall is structurally different from a plant cell wall because it contains which major structural polysaccharide?
Chitin
Plant cell walls primarily contain cellulose, while fungal cell walls contain chitin.
During fungal sexual reproduction, what is the difference between plasmogamy and karyogamy?
Plasmogamy is cytoplasmic fusion; karyogamy is nuclear fusion.
These events may be separated by a heterokaryotic or dikaryotic stage.
What are viruses that infect bacteria called?
Bacteriophages (phages).
These viruses infect bacterial host cells.
What is the name for viral DNA integrated into a bacterial chromosome during lysogeny?
Prophage.
The prophage is copied along with the host chromosome.
A fungal cell contains two separate haploid nuclei from different parents. Has karyogamy occurred? Explain.
No. The cell is dikaryotic, and its nuclei have not fused.
Karyogamy is nuclear fusion and produces a diploid nucleus.
A fungus grows through a decaying log. Explain how its hyphae obtain nutrients and why their structure is well suited for this process.
Hyphae secrete digestive enzymes into the log and absorb the resulting smaller molecules.
Their branching structure provides extensive surface area for absorption and lets the fungus penetrate its food source.
A fungal cell contains two genetically distinct haploid nuclei, written n + n, that have not fused. What is this condition called, and is the cell diploid?
Dikaryotic; no, the cell is not diploid.
The two haploid nuclei remain separate. A diploid nucleus forms only after karyogamy.
What are the three major capsid forms described in Chapter 19, and give an example of each.
Helical—tobacco mosaic virus; icosahedral—adenovirus; complex—T-even bacteriophage.
These examples illustrate different viral structural arrangements
What is the major difference between the lytic and lysogenic cycles?
The lytic cycle produces new phages and ends in host-cell lysis; the lysogenic cycle allows viral DNA to replicate with the host without immediately destroying it.
A temperate phage can switch from lysogeny to the lytic cycle.
A bacterial cell survives viral infection and passes viral DNA to its daughter cells. Which replication cycle best explains this observation?
Lysogenic cycle.
Integrated viral DNA can be copied during bacterial cell division without immediately destroying the host.
Two fungi have equal amounts of biomass. One grows as a compact mass, while the other forms an extensive network of thin, branching hyphae. Which would generally be more efficient at absorbing nutrients from its surroundings, and why?
he fungus with the extensive network of thin, branching hyphae.
Its higher surface-area-to-volume ratio and wider contact with the substrate improve nutrient absorption.
A fungal life cycle proceeds through plasmogamy, a prolonged dikaryotic stage, karyogamy, and meiosis. Explain how chromosome number and nuclear organization change across these stages.
Plasmogamy establishes an n + n stage; karyogamy produces a diploid (2n) nucleus; meiosis restores haploid (n) nuclei.
The dikaryotic stage has separate haploid nuclei, whereas the brief diploid stage follows nuclear fusion. Meiosis reduces chromosome number.
A virus cannot attach to a particular cell even though the cell has the resources needed to replicate viral material. Explain why infection may not occur.
The cell may lack a compatible surface receptor for the virus.
Host specificity depends partly on recognition between viral attachment proteins and host receptors.
A bacterium carrying a prophage divides repeatedly without releasing viruses. Later, an environmental signal causes production of new phages and destruction of the cell. Explain the transition.
The phage switches from the lysogenic cycle to the lytic cycle.
The prophage becomes active, directing viral production and eventual host-cell lysis.
A student claims that both fungal spores and viruses reproduce independently whenever conditions are favorable. Identify the error and explain the biological difference.
The claim is incorrect. Fungal spores can germinate and develop into fungi under suitable conditions, whereas viruses require living host cells to replicate.
Fungi are cellular organisms with their own metabolism; viruses lack the independent cellular machinery required for reproduction.