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 nutritionAbsorptive 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 hostsParasitic 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 fungusThe 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

LichensOne 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 flowsIn the arctic tundra, caribou graze on lichens at times of the year when other foods are unavailableAs 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 skinSome 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 antibioticsIn 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 hyphaeWithout 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?

1. Which of the following is a symbiotic relationship?

1. Penicellium2. Bread mold3. Yeast4. lichen

2. What do fungi produce that allows them to break down dead organisms?

3. How do humans use fungi?1. To flavor certain foods2. As a source of antibiotics3. As ingredients in baking and brewing4. All of the above

Questions?

4. What is an important role of fungi in an ecosystem?

5. What is the cause of the human disease ring worm?