Chapter 24

Study question

Which of the following statements is true?

A dikaryotic ascus that forms in the ascocarp undergoes karyogamy, meiosis, and mitosis to form eight ascospores.

Which of the following statements is true?

A basidium is the fruiting body of a mushroom-producing fungus, and it forms four basidiocarps.

if symbiotic fungi are absent from the soil, what impact do you think this would have on plant ?

without out mycorrhiza plants cannot absorb adequate nutrient which stunt their growth

Which polysaccharide is usually found in the cell wall of fungi?

chitin

Which of these organelles is not found in a fungal cell?

chloroplast

The wall dividing individual cells in a fungal filament is called a

septum

During sexual reproduction, a homothallic mycelium contains

both mating types

The life cycles of perfect fungi are most similar to which other organism?

Haploid-dominant green algae

The most primitive phylum of fungi is the ____

Chytridiomycota

Members of which phylum produce a club-shaped structure that contains spores?

Basidiomycota

Members of which phylum establish a successful symbiotic relationship with the roots of trees?

Glomeromycota

The fungi that do not reproduce sexually used to be classified as ____

Deuteromycota

A scientist discovers a new species of fungus that introduces genetic diversity during reproduction by creating a diploid zygote. This new species cannot belong to which modern phylum of fungi?

Deuteromycota

What term describes the close association of a fungus with the root of a tree?

a mycorrhiza

Why are fungi important decomposers?

They recycle carbon and inorganic minerals by the process of decomposition.

Consider an ecosystem where all the fungi not involved in mycorrhizae are eliminated. How would this affect nitrogen intake by plants?

Nitrogen intake would decrease.

A fungus that climbs up a tree reaching higher elevation to release its spores in the wind and does not receive any nutrients from the tree or contribute to the tree’s welfare is described as a

commensal

A fungal infection that affects nails and skin is classified as ___

superficial mycosis

The targets for anti-fungal drugs are much more limited than antibiotics or anti-viral medications. Why?

Human cells are much more similar to fungi cells than bacteria or viruses.

Yeast is a facultative anaerobe. This means that alcohol fermentation takes place only if:

the atmosphere does not contain oxygen

The advantage of yeast cells over bacterial cells to express human proteins is that:

yeast cells are eukaryotic and modify proteins similarly to human cells

Why are fungal insecticides an attractive alternative to chemical pesticides for growing food crops?

Human consumption of fungal insecticides would not make a person sick, but ingestion of chemical pesticides can be harmful to humans.

What are the evolutionary advantages for an organism to reproduce both asexually and sexually?

Asexual reproduction is fast and best under favorable conditions. Sexual reproduction allows the recombination of genetic traits and increases the odds of developing new adaptations better suited to a changed environment

Compare plants, animals, and fungi, considering these components: cell wall, chloroplasts, plasma membrane, food source, and polysaccharide storage. Be sure to indicate fungi’s similarities and differences to plants and animals.

.

Animals have no cell walls; fungi have cell walls containing chitin; plants have cell walls containing cellulose. Chloroplasts are absent in both animals and fungi but are present in plants. Animal plasma membranes are stabilized with cholesterol, while fungi plasma membranes are stabilized with ergosterol, and plant plasma membranes are stabilized with phytosterols. Animals obtain N and C from food sources via internal digestion. Fungi obtain N and C from food sources via external digestion. Plants obtain organic N from the environment or through symbiotic N-fixing bacteria; they obtain C from photosynthesis. Animals and fungi store polysaccharides as glycogen, while plants store them as starch.

Why is the large surface area of the mycelium essential for nutrient acquisition by fungi?

• Fungi break down decaying matter in their environment to serve as their food source. Since the digestion occurs externally, the large mycelium can secrete exoenzymes over a large area. The fungi must be able to absorb the small molecules released by digestion, so having a large surface area increases the amount of digested molecules that are captured by the fungi.

For each of the four groups of perfect fungi (Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota), compare the body structure and features, and provide an example.

• Chytridiomycota (Chytrids) may have a unicellular or multicellular body structure; some are aquatic with motile spores with flagella; an example is the Allomyces. Zygomycota (conjugated fungi) have a multicellular body structure; features include zygospores and presence in soil; examples are bread and fruit molds. Ascomycota (sac fungi) may have unicellular or multicellular body structure; a feature is sexual spores in sacs (asci); examples include the yeasts used in bread, wine, and beer production. Basidiomycota (club fungi) have multicellular bodies; features includes sexual spores in the basidiocarp (mushroom) and that they are mostly decomposers; mushroom-producing fungi are an example.

Ambrosia bark beetles carry Ambrosiella fungal spores to trees, then bore holes and lay their eggs with the fungus. When the new larvae hatch, they eat the fungus that has germinated in the holes. Describe how this relationship can be classified as mutualistic.

The bark beetles and the fungus have a mutualistic relationship since each partner benefits from interacting with the other. The beetle can provide food for its offspring, while the fungus can spread to new trees

Why can superficial mycoses in humans lead to bacterial infections?

• Dermatophytes that colonize skin break down the keratinized layer of dead cells that protects tissues from bacterial invasion. Once the integrity of the skin is breached, bacteria can enter the deeper layers of tissues and cause infections.

Historically, artisanal breads were produced by capturing wild yeasts from the air. Prior to the development of modern yeast strains, the production of artisanal breads was long and laborious because many batches of dough ended up being discarded. Can you explain this fact?

The dough is often contaminated by toxic spores that float in the air. It was one of Louis Pasteur’s achievements to purify reliable strains of baker’s yeast to produce bread consistently.