Exam Flashcards
1a. To which Domain of Life do fungi belong?
Fungi belong to the Eukarya doma
1b. Order the following, with closest relatives of us first. Plants, Fungi, Amoebas.
Closest relatives to us first: Fungi, Amoebas, Plants.
2a. Explain the way in which fungi obtain their nutrients
Fungi secrete enzymes into their environment to break down organic material, then absorb the nutrients.
2b. Is this way of feeding most similar to that of a) photosynthetic protists/plants, b) animals/closely related to us protists like amebae, or c) prokaryotes?
It is most similar to b) animals/closely related protists like amoebae.
- What 3 roles do fungi play in ecological communities?
- Decomposers, breaking down organic matter.
- Symbionts, forming mutualistic relationships like mycorrhizae.
- Pathogens, infecting plants and animals
Single-celled fungi are known a
Yeasts
Multicellular fungi are formed of filaments called
Hyphae
These filaments form a mass called a
Mycelium
Name the nitrogen-containing polysaccharide that is found in the cell walls of fungi.
Chitin
- What other group is able to produce and use the same substance?
Arthropods, in their exoskeletons
- The cross-walls that divide some fungal hyphae into cells are called
Septa
- What are Mycorrhizae?
Mycorrhizae are symbiotic associations between fungal hyphae and plant roots.
11a. What are the two types of Mycorrhiza, which of them is more efficient, and why it is more efficient?
The two types are ectomycorrhizae and endomycorrhizae. Endomycorrhizae are more efficient because they penetrate plant root cells, providing greater nutrient exchange.
11b. What benefits does each partner in Mycorrhiza bring to their relationship, and why is each partner better in providing these benefits than their partner?
The fungus provides the plant with nutrients like phosphorus and nitrogen, and the plant provides the fungus with carbohydrates. The fungus is better at nutrient absorption due to its extensive hyphal network, and the plant excels at photosynthesis for carbohydrate production.
- How is the role of spores in fungi different from that of endospores in prokaryotes?
Fungal spores are reproductive structures, while endospores in prokaryotes are survival structures formed under harsh condition
- Why are the hyphae long and thin?
To maximize surface area for nutrient absorption.
- Name one example of specialized hyphae (i.e., doing other things than the loose network of hyphae in the soil).
Haustoria, specialized hyphae that penetrate host tissues in parasitic fungi
- Describe the basic features of fungal sexual reproduction referring to graph below:
Fungal sexual reproduction involves plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei), and meiosis to produce spores.
- In what ways are fungal spores dispersed? What characteristics of fruiting bodies enhance dispersal?
Fungal spores are dispersed by wind, water, or animals. Fruiting bodies enhance dispersal with elevated structures, bright colors, or odors to attract dispersers.
17a. How do the spores of Chytrids differ from the spores of other fungi?
Chytrid spores are flagellated, allowing them to swim in water.
17b. How does chytrids lifestyles justify that difference in q.17?
Chytrids often live in aquatic environments, so flagellated spores help them move to new locations.
Chytrids are causing a serious disease in which two groups of animals?
Amphibians and fish.
Name the resistant structures formed by zygomycetes.
Zygosporangia
20a. Draw the life cycle of the zygomycete, Rhizopus stolonifer.
20b. Describe what happens during the life cycle of zygomycete, Rhizopus stolonifer.
The life cycle involves plasmogamy, formation of a zygosporangium, karyogamy, meiosis, and sporangia producing haploid spores
Why do zygomycetes “aim” their sporangia toward light?
To maximize spore dispersal by directing sporangia toward areas where conditions are favorable for growth.
Why are the Glomeromycetes important?
They form endomycorrhizae, crucial for nutrient exchange in many plants
23a. Ascomycetes produce sexual spores in these structures:
Asci
23b. Sexual spores produced by ascomycetes are called:
Ascospores
23c. Ascomycetes’ fruiting bodies are called:
Ascocarps
23d. Draw the life cycle of an ascomycete Neurospora crassa and describe it:
Drawing is required here.)
The life cycle involves:
1. Haploid spores germinate into hyphae.
2. Opposite mating types fuse in plasmogamy.
3. Dikaryotic cells form, then karyogamy occurs in the asci.
4. Meiosis produces haploid ascospores within asci, which are released and germinate.
23e. What are conidia and conidiophores?
Conidia are asexual spores, and conidiophores are specialized structures that produce conidia.
24a. The fruiting bodies of basidiomycetes are known as:
Mushrooms, with a well-known example being button mushrooms (Agaricus bisporus).
24b. In basidiomycetes, karyogamy and meiosis occur in structures called:
Basidia
24c. Describe the sexual life cycle of a mushroom-forming basidiomycete:
- Haploid spores germinate to form hyphae.
- Hyphae of opposite mating types fuse (plasmogamy), forming dikaryotic hyphae.
- Dikaryotic hyphae form a fruiting body (mushroom).
- Karyogamy occurs in basidia, followed by meiosis, producing haploid basidiospores.
24d. Draw the life cycle of a mushroom-forming basidiomycete:
Drawing is required here.
- Explain why decomposer fungi are essential components of Earth’s ecosystems:
Decomposer fungi recycle nutrients by breaking down organic material, enabling nutrient cycling and supporting plant growth.
26a. What is mutualism?
Mutualism is a symbiotic relationship where both species benefit.
26b. Fungi are involved in several types of mutualistic/symbiotic associations with other organisms. Explain the following:
Mycorrhizae: Symbiosis between fungal hyphae and plant roots; fungi provide nutrients, plants provide carbohydrates.
Endophytes: Fungi living inside plant tissues; they enhance stress resistance and deter herbivores.
Lichens: Symbiosis between fungi and photosynthetic partners (algae or cyanobacteria); fungi provide structure and moisture, while algae/cyanobacteria provide food via photosynthesis.
- Describe two mutualistic associations between fungi and animals that we discussed in class:
- Leaf-cutter ants and fungi: Ants cultivate fungi on chewed leaves, and the fungi provide the ants with food.
- Ruminants and fungi: Fungi in ruminant stomachs help digest cellulose.
28a. The example of formal infection by fungi:
Ringworm or athlete’s foot.
28c. Name the disease caused by a fungus that is seriously affecting bat populations in North America:
White-nose syndrome
28d. Explain how this fungus harms bats:
The fungus disrupts bats’ hibernation, causing them to deplete fat reserves and die from starvation.
- Explain some of the benefits/practical uses of fungi:
Fungi are used in food production (bread, beer, cheese), antibiotics (penicillin), biofuel production, and bioremediation
- What is a virus?
A virus is a non-cellular infectious agent made of genetic material (DNA or RNA) encased in a protein coat.
- What types of genomes can viruses have?
Viruses can have DNA or RNA genomes, which may be single-stranded or double-stranded.
- Virus genomes are enclosed by a protein coat called a:
Capsid, composed of subunits called capsomeres.
- What different shapes do viruses have? (Figure 19.3)
Helical, icosahedral, spherical, or complex shapes
5a. As well as nucleic acid and a protein coat, animal viruses may also have a(n)
Lipid envelope surrounding the protein coa
5b. How is this structure acquired?
It is acquired from the host cell membrane during viral budding.
5c. What benefits could the virus have from having this structure?
The envelope helps the virus evade the host immune system and aids in host cell entry.
5d. A virus may have glycoprotein spikes. One function of these spikes is:
To attach to specific receptors on host cells.
6a. What are bacterial viruses called?
Bacteriophages (phages).
6b. Describe the structure of bacterial viruses:
Bacteriophages have a capsid head containing the genome, a tail sheath, and tail fibers for attachment.
- Explain the terms:
Obligate intracellular parasites:
Organisms that can only reproduce inside a host cell.
Host: The organism a virus infects.
Host cell: The specific cell targeted by a virus.
Host range: The variety of hosts a virus can infect.
8a. What are the steps of virus reproductive cycles?
- Attachment.
- Entry.
- Genome replication.
- Assembly of new viruses.
- Release.
8b. What determines whether a virus attaches to a specific host cell?
The virus must match specific receptors on the host cell surface.
9a. What is a lytic cycle?
The lytic cycle is a viral replication process where the virus infects a host, replicates, and lyses (bursts) the host cell to release new virions
9b. A phage that only has a lytic cycle is called a:
Virulent phage
9c. What is the host for T4 phage? Describe/draw the steps in the T4 lytic cycle
The host is Escherichia coli.
Steps:
1. Attachment to host cell surface.
2. Injection of phage DNA.
3. Host machinery hijacked to replicate viral DNA and produce viral proteins.
4. Assembly of new phages.
5. Lysis of host cell to release phages.
(Drawing is required here.)
10a. Explain what a lysogenic cycle is.
The lysogenic cycle involves integration of viral DNA into the host genome, forming a prophage. The virus replicates passively with the host cell without killing it until triggered to enter the lytic cycle.
10b. Phages that have both lytic and lysogenic cycles are called:
Temperate phages.
10c. What is a prophage?
A prophage is a phage genome integrated into the host’s DNA during the lysogenic cycle.
11a. What is the host for phage λ (lambda)?
The host for phage λ is Escherichia coli (E. coli).
11b. Describe/draw the lytic and lysogenic cycles of phage λ:
- Lytic cycle: Similar to T4 cycle—phage DNA is replicated, and the host cell is lysed.
- Lysogenic cycle: Phage DNA integrates into the host genome as a prophage and replicates along with the host.
(Drawing required.)
- Lysogenic cycle: Phage DNA integrates into the host genome as a prophage and replicates along with the host.
11c. What factors may cause a virus to leave the lysogenic stage and enter the lytic stage?
Stress conditions such as UV light or chemical exposure can induce the prophage to excise itself and enter the lytic cycle.
11d. Why does this switch “make sense” from the point of view of a virus?
If the host is stressed and likely to die, switching to the lytic cycle ensures the virus reproduces before the host cell dies.
- What 3 types of defenses do bacteria have against phages?
- Restriction enzymes that cut phage DNA.
- CRISPR-Cas systems that recognize and destroy phage DNA.
- Blocking receptors to prevent phage attachment.
13a. What are the major types of animal viruses (based on their genome)?
- Double-stranded DNA viruses.
- Single-stranded DNA viruses.
- Double-stranded RNA viruses.
- Single-stranded RNA viruses (+ or - sense).
- Retroviruses.
13b. What are retroviruses, and why did we choose this name for them?
Retroviruses are RNA viruses that use reverse transcriptase to convert their RNA genome into DNA, which integrates into the host genome. The name “retro-” reflects the reversal of the usual DNA → RNA → protein flow.
14a. What specific type of cells are infected by HIV?
Helper T cells (CD4+ cells).
14b. Why is this serious/important?
Helper T cells are critical for coordinating the immune response, and their loss weakens the immune system, leading to AIDS
14c. Explain the replicative cycle of HIV. In your answer explain what reverse transcriptase is, and what a provirus is.
- HIV binds to CD4 receptors and fuses with the host cell.
- RNA genome is reverse-transcribed into DNA by reverse transcriptase.
- The viral DNA integrates into the host genome as a provirus.
- The host machinery transcribes and translates the provirus, producing viral proteins and genomes.
- New viruses are assembled and released via budding.
Reverse transcriptase: Enzyme that converts RNA into DNA.
Provirus: Integrated viral DNA that is permanently part of the host genome.
14d. What is a major difference between a prophage and a provirus?
A prophage can excise itself from the host genome and enter the lytic cycle, while a provirus is permanently integrated and cannot leave the host genome.
15a. Who evolved first - viruses or bacteria? Justify your answer.
Bacteria likely evolved first because they have cellular structures, which viruses lack. Viruses likely arose from fragments of cellular genomes.
15b. What are the three candidates for evolution into viruses?
- Escaped genetic material (plasmids or transposons).
- Degenerate cells that lost cellular functions.
- Remnants of pre-cellular life forms.
15c. All prokaryotes and eukaryotes evolved “once.” Can the same be said for viruses, or have they evolved many times? Justify your answer.
Viruses likely evolved multiple times because they vary greatly in structure and genetic material, suggesting independent origins.
- What is a Mimivirus?
A Mimivirus is a giant virus with a large genome, capable of infecting amoebas, and it blurs the line between viruses and cellular life.
17a. How do animal viruses cause the signs and symptoms of illness?
By damaging host cells through lysis, disrupting cell function, triggering immune responses, or hijacking cellular resources.
17b. What determines whether the damage done to us by viruses is reversible or permanent?
Reversibility depends on whether the infected cells can regenerate or recover, as well as the severity of immune system damage.
- What are emerging viruses? What are some examples?
Emerging viruses are newly identified or rapidly spreading viruses. Examples include SARS-CoV-2, Ebola, and Zika virus.
- What are the 3 factors important in the emergence and spread of emerging viruses?
- Mutations increasing infectivity or transmissibility.
- Cross-species transmission (e.g., animal to human).
- Globalization and population density increasing spread
- The original strains of COVID over time were being replaced by the new versions (“variants”). What are the three characteristics that helped the new variants in outcompeting the old ones, and if it is not already obvious - why these characteristics helped them to replace the earlier strains?
- Increased transmissibility: Allows variants to spread more efficiently in populations.
- Immune evasion: Variants can partially evade immunity from vaccines or prior infections, increasing their survival.
- Higher viral load: Produces more virus particles, enhancing transmission.
These characteristics make new variants more competitive, leading to their dominance over earlier strains.
