Protists and Fungi

Protists and Fungi Chapter 17.1, 18.1, & 18.3

Kingdom Protista: the most diverse of all eukaryotes Ch 17.1

Protists • Protists: eukaryotes that are not animals, plants, or fungi • Most protists are unicellular and free-living (not parasitic) • Protists have the typical eukaryotic cell structure, including internal membranes, a nucleus surrounded by a nuclear envelope, and organelles such as mitochondria and chloroplasts (in some species)

Protist Complexity • Being mostly unicellular, protists are considered the simplest form of eukaryotic organism • Most human cells are highly specialized, carrying out only certain tasks • The protist's one cell must consume and process food, respond to stimuli, excrete wastes, and reproduce • Protists can justifiably be considered the most complex of eukaryotic cells, since each cell must carry out all of an organism's life functions.

Protist nutrition used for classifying • Scientists group protists by lifestyle: animal-like, fungus-like, and plant-like protists • Protozoans: Animal-like; heterotrophs that ingest (eat) food • Algae: Plant-like; autotrophic making food through photosynthesis

Fungi Ch 18.1 & 18.3

Structure & Function of Fungi • Hypha: a thread of cytoplasm; many hyphae together make up the body of a fungus • Mycelium: interwoven mat of hyphae that functions as the feeding structure of a fungus • functions as the feeding structure of a fungus • fungal mycelium can grow as much as a kilometer of hyphae each day as it branches within its food

What’s the world’s largest organism? • Scientists have discovered one enormous mycelium in Oregon that measures 5.5 kilometers across and spreads through almost 9 square kilometers of forest (larger than 1,600 football fields) • Scientists also estimate that this fungus is at least 2,400 years old • Qualifies as one of Earth's oldest and largest living organisms

Mycelium • The branching mycelium enables the fungus to obtain food by absorptive nutrition • Absorptive nutrition: method by which fungi absorb small organic molecules from their surroundings • First, the fungus digests food outside its mycelium by secreting powerful enzymes into its surroundings • These enzymes break down complex molecules into smaller molecules the mycelium can absorb

Fungi’s role • Many fungi play an important role as decomposers • Fungi recycle nutrients such as nitrogen and carbon by breaking down organic material • Common food sources for fungi are fallen logs, bodies of dead animals, or the wastes of living organisms • Parasitic fungi absorb nutrients from the cells or body fluids of living hosts • Parasitic fungi cause about 80 percent of all plant diseases

Reproduction of Fungi • Fungi reproduce by releasing large numbers of microscopic spores • Spores: haploid single cell with a thick wall that functions in the dispersal stage in fungal reproduction • spread by the wind and can withstand unfavorable conditions for long periods of time • Most fungi produce spores asexually by mitosis at the tips of specialized hyphae • Many fungi also produce spores sexually • Haploid hyphae from different mycelia fuse together and combine their genetic material

Fungi have a major impact on other life Ch 18.3

Lichens • Lichens: mutualistic pairing of a fungus and an alga • The photosynthetic algae feed the fungus • The fungal mycelium provides a suitable habitat for the algae, helping to absorb and retain water and minerals • Lichen actually consists of millions of tiny algal cells within a mesh of fungal hyphae

Lichens • One benefit of symbiosis is that lichens are able to live in environments where neither fungi nor algae could live alone • Lichens are important pioneer organisms on newly cleared rock and soil surfaces, such as burned forests and volcanic flows • In the arctic tundra, caribou graze on lichens at times of the year when other foods are unavailable • As tough as lichens are, however, many do not tolerate air pollution • Their absorption of minerals from rain and moist air makes them particularly sensitive to chemicals such as sulfur dioxide • The death of sensitive lichens in an area can be an early warning of poor air quality.

Micorrhizae • Micorrhizae: symbiotic relationships between fungal hyphae and plant roots • The fungi absorb water and essential minerals from the soil and provide these materials to the plant • The fungal mycelium greatly increases the surface area of the root in contact with the soil, which increases the plant's absorption of water and minerals • The sugars produced by the plant nourish the fungi

Disease causing fungi • Of the 100,000 known species of fungi about 30 percent are parasites, mostly on or in plants • Dutch elm disease- has eliminated most elm trees in North America • The fungus was accidentally introduced into the United States on logs sent from Europe after World War I • Only about 50 species of fungus are known to be parasitic in humans and other animals • Among these are yeast infections of the lungs, some of which can be fatal • Other fungal parasites produce a skin disease called ringworm, so named because it appears as circular red areas on the skin • Some fungi attack the feet and cause intense itching and sometimes blisters- known as athlete's foot, is highly contagious, but it can be treated with various fungicides

Athlete’s Foot

Ring Worm

Commercial use of fungi • The distinctive flavors of certain kinds of cheeses come from the fungi used to "ripen" them • Yeasts are particularly important in baking, brewing, and winemaking • Used in making of antibiotics • In addition to edible mushrooms, other edible fungi include truffles • In nature, truffles release strong odors that attract mammals and insects that dig up the fungi and disperse their spores

Role of fungi in chemical cycling • Fungi and bacteria are the principal decomposers that supply ecosystems with the nutrients essential for plant growth • The air is so loaded with fungal spores that as soon as a leaf falls or an insect dies, it is covered with spores that quickly grow into fungal hyphae • Without decomposers, elements such as carbon and nitrogen would accumulate in organic matter • Plants and the animals they feed would starve because elements taken from the soil would not be returned

Questions? • Which of the following is a symbiotic relationship? • Penicellium • Bread mold • Yeast • lichen • What do fungi produce that allows them to break down dead organisms? • How do humans use fungi? • To flavor certain foods • As a source of antibiotics • As ingredients in baking and brewing • All of the above

Questions? • What is an important role of fungi in an ecosystem? • What is the cause of the human disease ring worm?

Protists and Fungi