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Printed: September 26, 2014 www.ck12.org Chapter 1. Protists and Fungi CHAPTER 1 Protists and Fungi CHAPTER OUTLINE 1.1 Protist Kingdom 1.2 Protist Evolution 1.3 Protist Characteristics 1.4 Protozoa 1.5 Algae 1.6 Molds 1.7 Protists and Human Disease 1.8 Fungi 1.9 Fungi Structure 1.10 How Fungi Eat 1.11 Fungi Reproduction 1.12 Fungi Evolution 1.13 Fungi Classification 1.14 Symbiotic Relationships of Fungi 1.15 Human Uses of Fungi 1.16 Fungi and Human Disease 1.17 References Introduction 1 www.ck12.org Would you eat this mushroom? Now that’s an interesting mushroom! In fact, fungi can be some of the most colorful species. And protists can be some of the most interesting. These two kingdoms which have some of the most diverse members are the first two eukaryotic kingdoms we discuss in the Protists and Fungi chapter. This quintessential toadstool, the fly agaric or fly Amanita, is a poisonous and psychoactive fungus. It has a large white-gilled, white-spotted, usually deep red mushroom, and it is one of the most recognizable and widely encountered in popular culture. You should not eat it. 2 www.ck12.org Chapter 1. Protists and Fungi 1.1 Protist Kingdom • Describe the protist kingdom. Prokaryote or eukaryote? This organism consists of a single cell with several flagella. Is it a prokaryote, such as a bacterium? Actually, it’s larger than a prokaryotic cell, and it also has a nucleus. Therefore, this organism belongs to the domain Eukarya, the domain that includes humans. This particular eukaryote is one of the smallest, simplest organisms in the domain, called a protist. It’s scientific name is Giardia lamblia. As a human parasite, it can make us sick. Kingdom Protista Protists are a group of all the eukaryotes that are not fungi, animals, or plants. As a result, it is a very diverse group of organisms. The eukaryotes that make up this kingdom, Kingdom Protista, do not have much in common besides a relatively simple organization. Protists can look very different from each other. Some are tiny and unicellular, like an amoeba, and some are large and multicellular, like seaweed. However, multicellular protists do not have highly specialized tissues or organs. This simple cellular-level organization distinguishes protists from other eukaryotes, such as fungi, animals, and plants. There are thought to be between 60,000 and 200,000 protist species, and many have yet to be identified. Protists live in almost any environment that contains liquid water. Many protists, such as the algae, are photosynthetic and are vital primary producers in ecosystems. Other protists are responsible for a range of serious human diseases, such as malaria and sleeping sickness. The term protista was first used by Ernst Haeckel in 1866. Protists were traditionally placed into one of several groups based on similarities to a plant, animal, or fungus: the animal-like protozoa, the plant-like protophyta (mostly algae), and the fungus-like slime molds and water molds. These traditional subdivisions, which were 3 1.1. Protist Kingdom www.ck12.org largely based on non-scientific characteristics, have been replaced by classifications based on phylogenetics (evo- lutionary relatedness among organisms). However, the older terms are still used as informal names to describe the general characteristics of various protists. FIGURE 1.1 Protists range from single-celled amoe- bas to multicellular seaweed. Protists may be similar to animals, plants, or fungi. Summary • Kingdom Protista includes all eukaryotes that are not animals, plants, or fungi. • Kingdom Protista is very diverse. It consists of both single-celled and multicellular organisms. Explore More Use this resource to answer the questions that follow. • Kingdom Protista at http://www.biologycorner.com/lesson-plans/phyla/kingdom-protista/. 1. List three characteristics of protists. 2. How are protists classified? 3. What is another name for animal-like protists and plant-like protists? 4. Complete this statement: Any eukaryote that is not a plant, animal or fungus is a __________. Explore More Answers 1. All protists are eukaryotic. Most are unicellular, but not all. Most live in water. 2. Protists are classified by how they obtain nutrition and how they move. 3. Animal-like Protists are also called protozoa. Plant-like Protists are also called alga. 4. Any eukaryote that is not a plant, animal or fungus is a protist. 4 www.ck12.org Chapter 1. Protists and Fungi Review 1. What are protists? 2. How are unicellular protists and multicellular protists similar? 3. How are protists classified? What are the main categories of protists? Review Answers 1. Protists are a group of all the eukaryotes that are not fungi, animals, or plants. 2. All protists, including multicellular protists, have a simple cellular-level organization. 3. Protists are classified by phylogenetics. The main categories of protists are the animal-like protozoa, the plant-like protophyta (mostly algae), and the fungus-like slime molds and water molds. 5 1.2. Protist Evolution www.ck12.org 1.2 Protist Evolution • Outline the evolution of protists. • Explain the formation of the first eukaryotic cells. • Site evidence for the endosymbiotic theory. What’s the difference between a bacterium and a simple protist? Were simple protists the first eukaryotic organisms to evolve? Probably. A protist is a eukaryote, so each cell has a nucleus. Otherwise, simple protists, like the Paramecium and amoeba, can be fairly similar to bacteria. Evolution of Protists Scientists think that protists are the oldest eukaryotes. If so, they must have evolved from prokaryotic cells. How did this happen? The endosymbiotic theory provides the most widely-accepted explanation. That’s because it is well supported by evidence. The First Eukaryotic Cells According to the endosymbiotic theory, the first eukaryotic cells evolved from a symbiotic relationship between two or more prokaryotic cells. Smaller prokaryotic cells were engulfed by (or invaded) larger prokaryotic cells. The small cells (now called endosymbionts) benefited from the relationship by getting a safe home and nutrients. The large cells (now called hosts) benefited by getting some of the organic molecules or energy released by the endosymbionts. Eventually, the endosymbionts evolved into organelles of the host cells. After that, neither could live without the other. 6 www.ck12.org Chapter 1. Protists and Fungi As shown in Figure 1.2, some of the endosymbionts were aerobic bacteria. They were specialized to break down chemicals and release energy. They evolved into the mitochondria of eukaryotic cells. Some of the small cells were cyanobacteria. They were specialized for photosynthesis. They evolved into the chloroplasts of eukaryotic cells. FIGURE 1.2 Endosymbiotic theory explains how eukaryotic cells arose. Evidence for the Endosymbiotic Theory Many pieces of evidence support the endosymbiotic theory. For example: • Mitochondria and chloroplasts contain DNA that is different from the DNA found in the cell nucleus. Instead, it is similar to the circular DNA of bacteria. • Mitochondria and chloroplasts are surrounded by their own plasma membranes, which are similar to bacterial membranes. • New mitochondria and chloroplasts are produced through a process similar to binary fission. Bacteria also reproduce through binary fission. • The internal structure and biochemistry of chloroplasts is very similar to that of cyanobacteria. Summary • Scientists think that protists are the oldest eukaryotes. • Protists most likely evolved from prokaryotic cells, as explained by the endosymbiotic theory. This theory is well-supported by evidence. Explore More Use this resource to answer the questions that follow. 7 1.2. Protist Evolution www.ck12.org • It Takes Teamwork: How Endosymbiosis Changed Life on Earth at http://evolution.berkeley.edu/evolib rary/article/endosymbiosis_01. 1. What were the predecessors of eukaryotic cells? 2. What is endosymbiosis? 3. What may have been the first internal symbiotic relationship? Explain this relationship. 4. Why is DNA considered evidence for endosymbiosis? Explore More Answers 1. Eukaryotic cells are actually the descendents of separate prokaryotic cells that joined together in a symbiotic union.