Chapter 34 Summary
Core Concepts Summary
34.1 Fungi are heterotrophic eukaryotes that feed by absorption.
Fungi are heterotrophs that depend on preformed organic molecules for both carbon and energy. page 716
Fungi break down their food and then absorb it. page 716
Fungi use the process of growth to find and obtain food in their environment. page 716
Most fungi have numerous branched filaments called hyphae, which absorb nutrients. page 716
When fungi encounter a rich source of food, their hyphae form a network called a mycelium. page 716
Fungal cell walls are made of chitin, the same compound found in the exoskeletons of insects. page 716
In early fungal groups, the hyphae form a continuous compartment, with many nuclei but with no cell walls, but in later evolving groups, nuclear divisions are accompanied by the formation of septa that divide the cytoplasm into separate cells. page 717
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Some fungi, such as yeasts, do not produce hyphae. page 717
Most fungi feed on dead organic matter. page 718
Fungi are critical elements of the carbon cycle, converting dead organic matter back into carbon dioxide and water. page 718
Many fungi feed on living animals and plants, causing diseases. page 718
Fungi have repeatedly evolved mutually beneficial relationships with plants and animals. page 720
Lichens are stable associations between a fungus and a photosynthetic microorganism that look, function, and even reproduce as single organisms page 720
34.2 Fungi reproduce both sexually and asexually, and disperse by spores.
Fungi produce haploid spores that are dispersed by wind, water, or animals. page 722
Spores can be produced asexually (by mitosis) or sexually (by cell fusion and meiosis). page 722
During sexual reproduction, many fungi produce spores within multicellular fruiting bodies that enhance spore dispersal. page 723
The fungal life cycle is similar to haploid-
Genetically determined mating types prevent self-
Asexual fungal species have mechanisms for generating genetic diversity; these are thought to involve fusion of haploid nuclei, followed by crossing over during mitosis and chromosome loss. page 726
34.3 Other than animals, fungi are the most diverse group of eukaryotic organisms.
About 75,000 fungal species have been formally described, but total diversity may be as high as 5 million species. page 726
Chytrids are the first diverging groups of fungi. They occur in aquatic or moist habitats and only about 1000 species have been identified. page 727
Zygomycetes produce hyphae without septa and make up less than 1% of known fungal species. page 728
The glomeromycetes are a group of fungi of low diversity but tremendous ecological importance because of their association with plant roots. page 728
Most fungi belong to the Dikarya (ascomycetes and basidiomycetes), which form septa along hyphae. During the heterokaryotic stage, these fungi produce cells that contain two haploid nuclei, one from each parent. page 728
Ascomycetes include wood-
Basidiomycetes include familiar toadstools and puffballs, as well as plant pathogens page 732
Self-Assessment
Describe two ways in which fungi differ from other heterotrophic organisms in how they obtain and digest their food.
Self-Assessment 1 Answer
Fungi do not have organs that enable them to ingest and digest food. Instead, fungi absorb molecules directly through their cell walls after they have first digested the material through the release of enzymes. Fungi are also unable to move to find food; thus, they grow to find nourishment.
Explain how hyphae and cell walls made of chitin allow fungi to obtain nutrients from their environment.
Self-Assessment 2 Answer
Hyphae are numerous long, thin filaments that provide a large surface area for absorbing nutrients. Hyphae grow at the tip, elongating and penetrating into new environments where they may encounter water and new food resources. Chitin allows the cell walls of hyphae to be flexible but strong compared to plant cell walls. The cell wall also prevents the cell from rupturing, and it contributes to the formation of positive turgor pressure, the force that allows the hyphae to penetrate deeper into their surroundings.
Describe how fungi contribute to the terrestrial carbon cycle.
Self-Assessment 3 Answer
Fungi convert dead organic matter back to CO2 and water, thus returning nutrients to the soil where they will be available for plant growth. In particular, fungi are the major decomposers of the cellulose and lignin in wood.
Name the two organisms that make up a lichen and describe how each partner benefits from the association.
Self-Assessment 4 Answer
Lichens are made up of a fungus and a photosynthetic microorganism such as green algae or cyanobacteria. The hyphae of the fungus anchor the lichen, aid in the uptake and retention of water and nutrients, and produce chemicals that protect against excess light and herbivorous animals. The photosynthetic microorganism provides a source of reduced carbons and, in some cases, fixed nitrogen.
Describe how fungi disperse.
Self-Assessment 5 Answer
Fungi disperse through the release of spores. A fungus will produce a huge number of spores that will be carried by the wind, water, or animals to different environments. A spore will start to grow only if it is in a suitable environment.
Draw the life cycle of an ascomycete, and indicate the heterokaryotic stage.
Self-Assessment 6 Answer
Draw the life cycle of a basidiomycete, and indicate the heterokaryotic stage.
Self-Assessment 7 Answer
Name and describe several key innovations in the evolutionary history of fungi that allowed them to move from water to land.
Self-Assessment 8 Answer
Several key innovations in the evolutionary history of fungi allowed these organisms to move from water to land. The first is hypha―elongate cells that permitted fungi to explore the land environment in search of nutrients and water. Second, the evolution of aerial spores and the structures releasing them helped fungi disperse their spores successfully on land.
Explain how the evolution of vascular plants has provided opportunities for fungal diversification.
Self-Assessment 9 Answer
The larger bodies and greater productivity of vascular plants have allowed fungi to diversify by permitting them to specialize on different food resources―for example, by decomposing leaves or wood, or by entering into symbiotic relationships with plant roots.