fungi

How do fungi obtain nutrients?

Fungi are heterotrophs that feed by absorption. They secrete hydrolytic enzymes into their surroundings to break down complex molecules into smaller organic compounds that they can absorb into their cells.

What are fungal cell walls made of, and why?

The cell walls are made of chitin, which provides structural support and resists the water pressure (osmotic pressure) created as nutrients are absorbed into the cells.

What is the difference between septate hyphae and coenocytic hyphae?

1. Septate hyphae: Divided into cells by cross-walls called septa, which have pores for the flow of organelles.
2. Coenocytic hyphae: Lack septa and consist of a continuous cytoplasmic mass with hundreds or thousands of nuclei due to nuclear division without cytokinesis.

What is a mycelium?

An interwoven mass formed by fungal hyphae that infiltrates the material on which the fungus feeds. Its structure maximizes the surface-to-volume ratio for efficient absorption.

Define Mycorrhizae

Mutually beneficial relationships between fungi and plant roots where the fungi improve mineral delivery (like phosphate ions) to the plant, while the plant supplies the fungi with organic nutrients like carbohydrates.

Explain Plasmogamy, Heterokaryon, and Karyogamy

• Plasmogamy: The union of the cytoplasms of two parent mycelia.
• Heterokaryon: A stage where the haploid nuclei from two parents coexist in the mycelium without fusing.
• Karyogamy: The fusion of the two haploid nuclei, resulting in a diploid (2n) cell.

What are Chytrids?

A basal fungal lineage often found in lakes and soil. They are unique among fungi because they possess flagellated spores called zoospores.

Distinguishing features of Ascomycetes

Known as "sac fungi," they produce sexual spores (ascospores) in saclike asci. They also produce asexual spores called conidia at the tips of specialized hyphae (conidiophores).

Distinguishing features of Basidiomycetes

Known as "club fungi," they are defined by a cell called a basidium where karyogamy occurs. They are important decomposers of wood (lignin) and produce fruiting bodies called basidiocarps (mushrooms).

What is a Lichen?

A symbiotic association between a photosynthetic microorganism (green algae or cyanobacteria) and a fungus (usually an ascomycete). The photosynthetic partner provides carbon/nitrogen, while the fungus provides a protected environment and minerals.

What is Mycosis?

A general term for an infection in an animal caused by a fungal parasite, such as ringworm, athlete's foot, or systemic infections like those caused by Candida albicans.

Arbuscular Mycorrhizal Fungi vs. Ectomycorrhizal Fungi

• Arbuscular: Extend specialized branching hyphae (arbuscules) through the root cell wall and into the cell membrane.
• Ectomycorrhizal: Form sheaths of hyphae over the root surface and grow into the extracellular spaces of the root cortex.

What was the ancestor of fungi according to phylogenetic analysis?

Fungi evolved from a unicellular, flagellated, aquatic protist. Evidence shows they are more closely related to animals than to plants.

What are fungal endophytes, and how do they benefit plants?

Endophytes are fungi (typically ascomycetes) that live inside the leaves or other plant parts without causing harm. They help by:

• Producing toxins that deter herbivores.
• Increasing plant tolerance to heat, drought, or heavy metals.
• Defending against plant pathogens.

How do yeasts reproduce asexually?

Yeasts reproduce asexually through ordinary cell division (mitosis) or by the pinching off of small bud cells from a parent cell.

Distinguishing features of Cryptomycetes and Microsporidians

• Cryptomycetes: Unicellular, flagellated spores, found in soil and water, often parasites of protists.
• Microsporidians: Unicellular parasites of animals and protists with highly reduced mitochondria and small genomes; they infect hosts via a harpoon-like organelle.

What are the key characteristics of Zoopagomycetes?

Most are parasites or commensal symbionts of animals. They produce non-flagellated spores dispersed by wind and form a zygosporangium during sexual reproduction to protect the zygote.

Detail the sexual reproduction of Mucoromycetes (e.g., Rhizopus stolonifer)

Plasmogamy produces a zygosporangium, a sturdy structure that is first heterokaryotic and then becomes diploid (2n) after karyogamy. It is metabolically inactive and resists freezing/drying until conditions improve for meiosis and germination.

What is a dikaryotic mycelium?

A stage in the life cycle where haploid nuclei from two parents pair off two to a cell. As the mycelium grows, the two nuclei divide in tandem, maintaining the (n + n) state before eventual karyogamy.

How do lichens reproduce asexually?

They can reproduce by fragmentation or by the formation of soredia, which are small clusters of hyphae with embedded algae/cyanobacteria that act as a symbiotic unit for dispersal.

What are some medical and research uses of fungi?

• Medicine: Ergots provide compounds to reduce high blood pressure; fungi produce antibiotics like penicillin.
• Research: The yeast Saccharomyces cerevisiae is a model organism for eukaryotic genetics and studying diseases like Parkinson's.

How have chytrid fungi impacted global biodiversity?

The chytrids Batrachochytrium dendrobatidis and B. salamandrivorans cause lethal skin infections in amphibians, leading to the severe decline or extinction of hundreds of species.