Diversity: From Simple to Complex

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1 CHAPTER 2 Diversity: From Simple to Complex Specific Expectations B1.2 analyze the impact that climate change might have on the diversity of living things (2.4) B2.1 use appropriate terminology related to biodiversity (2.2) B2.3 use proper sampling techniques to collect organisms from an ecosystem and classify the organisms according to the principles of taxonomy (2.4) B3.2 compare and contrast the structure and function of different types of prokaryotes, eukaryotes, and viruses (2.1, 2.2, 2.3) B3.3 describe unifying and distinguishing anatomical and physiological characteristics of representative organisms (2.2, 2.4) B3.4 explain key structural and functional changes in organisms as they have evolved over time (2.1, 2.3) Why are scientists from the Canadian Space Agency and universities interested in this strange looking structure at the bottom of Pavilion Lake in British Columbia? This mound and many others like it in the lake are covered with different types of bacteria and other micro-organisms that trap minerals from the water to form the solid structures beneath them. These structures, called microbialites, were common on Earth from 2.5 billion to 540 million years ago, and scientists hope to gain insight into the history of life on Earth by studying them. Since these structures are usually found in harsh environments, similar to some of the conditions on Mars and other solar bodies, understanding more about how they form may also help scientists in recognizing past or present extraterrestrial life. 50 MHR Unit 1 Diversity of Living Things

2 Launch Activity Classifying the Invisible Micro-organisms, such as bacteria and protists, range in size from m to m, and smaller. What characteristics would you use to classify three microscopic entities? Use your observations of prepared slides or the photograph below to determine some of the differences among bacteria, protists, and viruses. Bacterium (E. coli) Magnification: 3000 Protist (Amoeba) Magnification: 85 Influenza Virus Magnification: Materials light microscope prepared slide of a bacterial species prepared slide of a protist picture of a virus Procedure 1. Observe the slide of the bacterium. (Alternatively, you can observe the photograph above.) Make a sketch, labelling all the structures you recognize for example, cell membrane, flagellum, cilia. 2. Repeat step 1 with the protist and the virus. 3. Estimate and record the size of each bacterium, protist, and virus. Go to Using a Microscope Appendix A to learn more about how to estimate the size of a specimen. 4. Use a table or graphic organizer to compare and contrast bacteria, protists, and viruses, based on your observations. Questions 1. What do viruses, protists, and bacteria have in common? 2. Which characteristic(s) do you think scientists use to help them distinguish among viruses, protists, and bacteria? Explain your answer. Chapter 2 Diversity: From Simple to Complex MHR 51

3 SECTION 2.1 Key Terms virus capsid replication lytic cycle lysogenic cycle prion A Microscopic Look at Life s Organization Take a moment to think about the differences among the three organisms shown in Figure 2.1: E. coli bacteria, a blue whale, and western red cedar trees. Each of these organisms contains cells that are different from the cells contained in the others, such as the animal cells in the whale and the plant cells in the trees. The organisms also have different external and internal structures. In other words, these organisms exhibit structural diversity. In organisms as large as blue whales or western red cedar trees, there is a range of complexity both within their cells and in the way those cells are organized in the whole organism. In unicellular organisms, such as bacteria, structural diversity exists at the cellular level. A Figure 2.1 The millions of species on Earth demonstrate tremendous structural diversity. (A) E. coli bacteria are microscopic, unicellular, and reproduce asexually. Blue whales (B) and western red cedar trees (C), are huge, multicellular, and reproduce by sexual means. C Magnification: 5800 B Describe one example of structural diversity among the organisms shown. The cells of multicellular organisms undergo division in order to grow and reproduce. There are two types of cell division: mitosis and meiosis. (Cell division in unicellular organisms is of a different type, as you will learn later in this chapter.) During mitosis, cells divide to form two cells that are identical to the parent cell. Meiosis produces the reproductive cells (egg and sperm), which have half the number of chromosomes as the parent cell. Meiosis contributes to genetic diversity. 52 MHR Unit 1 Diversity of Living Things

4 Prokaryotes and Eukaryotes The study of cells is an important first step in understanding the diversity of life. Recall from Chapter 1 that biologists recognize two basic types of cells based on differences in their size, structure, and other characteristics, as shown in Table 2.1. Bacteria and archaea are prokaryotes, whose cells lack a true nucleus. Protists, plants, fungi, and animals are eukaryotes. Recall that eukaryotic cells are larger and more complex than prokaryotic cells, and they do contain nuclei and other membrane-bound organelles. Table 2.1 Two Types of Cells Characteristic Prokaryotes: Bacteria, Archaea Eukaryotes: Protists, Plants, Fungi, Animals Size 1 10 μm μm Genetic material circular DNA, not bound by a membrane genome made up of a single chromosome DNA in nucleus bounded by membrane genome made up of several chromosomes Cell division not by mitosis and meiosis by mitosis and meiosis Reproduction asexual reproduction common sexual reproduction common Number of cells unicellular most forms are multicellular Organelles Metabolism mitochondria and other membranebound organelles absent many are anaerobic (do not require oxygen to carry out cellular respiration) mitochondria and other membranebound organelles present most are aerobic (require oxygen to carry out cellular respiration) Viruses Viruses differ from both prokaryotic and eukaryotic cells in several fundamental ways. The first is that viruses are functionally dependent on the internal workings of cells either prokaryotic or eukaryotic. Viruses are not capable of living independently outside of cells. They must invade cells and use the host cell s machinery for survival and reproduction. Outside a cell, viruses are dormant. Viruses also differ structurally from prokaryotic and eukaryotic cells. Viruses are not cellular, so they have no cytoplasm, membrane-bound organelles, or cell membranes. For these reasons, some scientists do not consider viruses to be living organisms. Although viruses are incapable of living independently and are not considered living by some scientists, they do affect the lives of other organisms. Viruses cause disease in plants and animals, which can affect populations, species, and ecosystems. Certain viruses infect plants, such as wheat, oats, and barley, that are grown as food sources for humans. Uncontrolled infection can lead to food shortages in some areas of the world. Other viruses, such as the polio virus, HIV, and H1N1, infect humans, leading to severe illness. Scientists develop vaccines and new treatments to fight viral infections. Viruses are also used in biotechnology to clone copies of genes. virus a structure that contains strands of DNA or RNA surrounded by a protective protein coat; it cannot live independently outside of cells Chapter 2 Diversity: From Simple to Complex MHR 53

5 capsid the outer protein layer that surrounds the genetic material of a virus replication the fundamental process of all cells, in which the genetic material is copied before the cell reproduces lytic cycle the replication process in viruses in which the virus s genetic material uses the copying machinery of the host cell to make new viruses lysogenic cycle the replication process in viruses, in which the viral DNA enters the host cell s chromosome; it may remain dormant and later activate and instruct the host cell to produce more viruses Classifying Viruses Because viruses are not cellular they are not formally considered to be organisms. This means they are not included in the classification of life, covered in Chapter 1. However, since they have genetic material and reproduce, there are good reasons for considering them to be alive. Biologists involved in studying viruses do have a system to classify and name them, but this system is not part of the classification system of life. One of the methods used by scientists to classify viruses is the size and shape of the capsid, shown in Figure 2.2. A capsid is the protein coat that surrounds the genetic material, either DNA or RNA, of a virus. Some viruses, such as the polio virus, resemble small crystals and may have as many as 20 sides. The HIV that causes AIDS has a spherical shape. The tobacco mosaic virus, which infects tobacco plants, has a cylindrical shape. The T4 virus infects bacteria. It has a head attached to a protein tail and several tail fibres. Viruses are also grouped by the types of diseases they cause. Viruses that infect humans are currently classified into 21 groups. These groups differ in their genomes, or sets of genes, and their method of replication. A C B D Figure 2.2 Viruses have a variety of shapes. The viruses shown here include (A) the polio virus, (B) HIV, (C) the tobacco mosaic virus, and (D) the T4 virus. Describe the differences among the capsids of the viruses shown here. Reproduction in Viruses Since viruses are not cellular, they do not reproduce by cell division. Instead, they are said to undergo replication within a host cell. The host cell can be either a prokaryote or a eukaryote, depending on the virus type. Viruses use the host cell to produce multiple copies of themselves. Then the copies are assembled by the host cell inside it. The typical replication cycle of viruses, shown in Figure 2.3, is called the lytic cycle. Sometimes the genetic material of the virus enters the nucleus of the host cell. In the lysogenic cycle, also shown in Figure 2.3, the viral DNA enters and becomes part of the host cell s chromosomes. Once this occurs, the infected cell has viral genes permanently. The viral DNA that has become part of the host chromosome is then referred to as a provirus. A provirus can invade a cell, but does not kill it. 54 MHR Unit 1 Diversity of Living Things

6 Lysis and Release: The host cell breaks open and releases new viral particles. Attachment: Proteins on the surface of the virus bind to protein receptors on the surface of the host cell s membrane. DNA or RNA bacterial cell wall capsid bacterial chromosome Lytic Cycle Assembly: New viral particles are assembled. Entry: The virus injects its genetic material (RNA or DNA) into the host cell. Replication: The host cell makes more viral DNA or RNA and proteins. Provirus Formation: Viral DNA becomes part of the host cell s chromosome. Lysogenic Cycle Provirus leaves the host s chromosome. cell division Provirus replicates with host s chromosome. Figure 2.3 In the lytic cycle, the entire replication process occurs in the cytoplasm of the host cell. The virus s genetic material enters the host cell, and the cell replicates the viral DNA or RNA. The host cell makes new capsids and assembles new viral particles. The host cell lyses, or breaks open, and the new viruses leave the cell. In the lysogenic cycle, the virus s genetic material enters the host cell s chromosome. In many cases, the genes are not activated until later. Activation results in a continuation of the lytic cycle. Learning Check 1. What does the term structural diversity describe? 2. Make an argument for or against the following statement: Viruses are living organisms. 3. Make a graphic organizer to explain the differences among prokaryotes, eukaryotes, and viruses. 4. Describe how scientists classify viruses. 5. Identify the differences between the lytic and lysogenic cycles involved in viral replication. 6. The soil-borne wheat mosaic virus causes disease and yield loss in crops such as wheat and barley. Predict the impact of an uncontrolled infection of this viral disease. Chapter 2 Diversity: From Simple to Complex MHR 55

7 Viruses and Disease In the lytic cycle of a virus, newly formed viruses burst from the host cell, usually killing it. In multicellular hosts, these new viruses then infect neighbouring cells, causing damage to their host. The amount of damage and its effects on the host vary. In viruses that undergo the lysogenic cycle, effects on the host may not be immediate. For instance, the human immunodeficiency virus (HIV) is an example of a type of virus called a retrovirus. Retroviruses contain an enzyme called reverse transcriptase. As you can see in Figure 2.4, this enzyme causes the host cell to copy the viral RNA into DNA. In this form, the viral DNA enters the chromosomes of the host cell, so it is a provirus. When the host cell divides by mitosis, it replicates the provirus along with its own DNA. Every descendant of the host cell carries a copy of the provirus in its chromosomes. This process can continue for years, with no harm to the host. Because the virus is part of the host chromosomes, it cannot be easily detected by medical tests. At any time, however, the provirus can separate from the host chromosomes and complete the more damaging lytic cycle. SuggestedInvestigation ThoughtLab 2-A, Measles Immunization Patterns of Disease The replication strategies of viruses help explain certain patterns of disease. For example, the herpes simplex virus causes cold sores in humans. These sores may appear and disappear on the skin of infected people throughout their lifetime. The sores appear when the viral cycle destroys cells, and they disappear when the virus is in its provirus stage. The exact trigger that causes the switch from one phase to another is not known. Other viruses follow variations of the replication strategies already described. For example, HIV forms a provirus in the host cell chromosomes, but it also produces small numbers of new viruses while the cell continues to function normally. This explains why people may test positive for HIV and still remain healthy for many years. Only when the infection spreads to more and more cells do the symptoms of AIDS (acquired immune deficiency syndrome) eventually appear. The symptoms result from infections by other micro-organisms, because the HIV has destroyed the body s T-lymphocytes, which help the immune system fight off other diseases. retrovirus RNA DNA RNA DNA is made from the viral RNA reverse transcriptase entering cell Retrovirus cycle provirus in host chromosome mrna new virus parts exiting cell new virus forming Figure 2.4 Retroviruses contain an enzyme that causes the host cell to copy viral RNA into DNA. This DNA becomes a provirus that continues to produce new viruses without destroying the cell. 56 MHR Unit 1 Diversity of Living Things

8 Prions: Non-viral Disease-causing Agents For many years, scientists worked to determine the cause of several types of brain diseases in which the disease is usually not detected for decades after a person is infected. This sounds like the pattern of a viral infection. However, scientists noted that the infectious agent remained infectious even after it was exposed to radiation, which would destroy the DNA or RNA. In the 1980s, American researcher Stanley Prusiner discovered an entirely new type of disease-causing agent called a prion. The discovery was remarkable for two reasons. First, prions are proteins that are found normally in the body. Second, they are the only known disease-causing agents that lack RNA or DNA. Diseases result when prions convert from their normal form into harmful particles that have the same chemical composition but a different molecular shape. Prions cause several deadly brain diseases, including Creutzfeldt-Jakob disease (CJD) in humans, scrapie in sheep, and bovine spongiform encephalopathy (BSE) or mad cow disease in cows. prion an infectious particle that causes damage to nerve cells in the brain, and that appears to consist mostly or entirely of a single protein Viruses and Biotechnology Because viruses enter host cells and direct the activity of the host cell s DNA, they can be useful tools for genetic engineers. For example, if researchers want to make a copy of a gene, they first insert the gene into the genetic material of a virus. The virus then enters a host cell and directs the cell to make multiple copies of the virus. Each new virus in each new cell contains the added gene that the researchers want copied. Activity 2.1 Comparing Prion Diseases Creutzfeldt-Jakob disease (CJD) and Variant Creutzfeldt- Jacob disease (vcjd) are two neurological diseases caused by prions. CJD was first recognized by scientists in the 1920s and occurs worldwide at a rate of about one case per million people. vcjd was first described by scientists in Since then, about 200 people worldwide have been diagnosed with vcjd. In this activity, you will compare the characteristics of these diseases, including symptoms and test results. A confirmed diagnosis can only be achieved by examining the brain tissue of the patient after death. Procedure Use the table on the right to answer the questions. Questions 1. Suppose you are a doctor looking at the magnetic resonance imaging (MRI) results of your patient. If your patient has vcjd, what do you expect the MRI to show? Explain your reasoning. 2. If your patient has vcjd, do you expect to see abnormal clusters of proteins in his or her brain tissue? Explain your reasoning. 3. You have a 60-year-old patient who has been experiencing symptoms such as memory loss and difficulty with coordination for about three months. Without further testing, which disease do you suspect your patient has? What test results do you expect to see to confirm this diagnosis? Characteristics of Two Prion Diseases Characteristic CJD vcjd Median age at death 68 years 28 years Median length of 4 5 months months illness Symptoms Periodic sharp waves recorded during test that measures electrical activity in brain Abnormal signals in certain regions of the brain on an MRI Presence of prions in lymph tissue Abnormal clusters of protein fragments in brain tissue* Memory loss, difficulty communicating, inability to reason, difficulty with coordination and movement Often present Not reported Not readily detected Rare or absent Psychiatric and behavioural symptoms, painful distortion of sense of touch Often absent Present in over 75 percent of cases Readily detected Present in large numbers *Confirmed through tests performed after the death of the patient Chapter 2 Diversity: From Simple to Complex MHR 57

9 Section 2.1 REVIEW Section Summary There are two basic cell types prokaryotic cells and eukaryotic cells. Prokaryotic cells are smaller and less complex than eukaryotic cells. Prokaryotic cells do not have a membrane-bound nucleus or other membrane-bound organelles. Because viruses cannot function independently in any way, some scientists believe they are not living organisms. Viruses can be classified by the size and shape of their capsid. Viruses reproduce through replication within a host cell. They replicate through the lytic cycle or the lysogenic cycle. Prions are infectious particles that appear to consist mostly or entirely of a single protein. Review Questions 1. K/U List three differences between prokaryotic cells and eukaryotic cells. 2. A Classify each of the organisms shown in Figure 2.1 as either prokaryotes or eukaryotes. Explain your reasoning. 3. C Viral replication can be compared to making a product in a factory. Explain how, and identify the strengths and weaknesses of this comparison. 4. C Draw a diagram to demonstrate how viruses might be used to copy the genes for producing human insulin. 5. A Incubation time is the time for symptoms of a disease to occur after exposure. Consider the data on the incubation time of different viral diseases in the table below. Use the data to predict which diseases are caused by viruses that undergo the lytic cycle and which are caused by viruses that undergo the lysogenic cycle. What is a possible public health consequence of the incubation time for diseases caused by proviruses? Incubation Time of Viral Diseases Disease Measles Shingles Warts Cold HIV Incubation Time 9 11 days Years Months 2 4 days 2 5 years 6. T/I If you were a scientist developing a drug that would block viral replication, which steps would you choose to block? (Hint: Refer to Figure 2.3.) Explain your answer in detail. 7. C Viruses replicate; they do not reproduce. Most viruses replicate through the lytic cycle. Create a flowchart or point-form outline of the lytic cycle. 8. C Illustrate the differences among a virus, a prokaryotic cell, and a eukaryotic cell. 9. T/I What advantages do you think viruses might have over cells? 10. K/U These disease-causing agents are not bacterial, fungal, or a virus. They contain no genetic material, yet they are responsible for a number of degenerative brain diseases. Identify these agents and describe how they cause these diseases. 11. K/U Why are new retroviruses in humans difficult to detect? 12. C Define the term provirus. Use Figure 2.4 as a guide to make a flowchart or other graphic organizer to explain how a retrovirus, such as HIV, develops into a provirus. 13. A Originally, some viruses, such as the Epstein-Barr virus, were named for the scientists who discovered them. Others diseases, such as dengue fever or influenza, were named for the way people imagined they were contracted. Explain why virologists today are attempting to develop a standardized scientific naming system. 14. T/I In a normal cell, DNA is transcribed into RNA, and then the RNA is translated into proteins. However, when a retrovirus is inside of a cell, the first two steps of that process are switched. Rather than DNA RNA protein, it is RNA DNA. Reverse transcription lacks the usual proofreading of DNA replication. As a result, a retrovirus can mutate often. Predict the impact of rapidly mutating viruses on the development of effective treatments, such as anti-viral medications. 15. C Use a Venn diagram or other graphic organizer to compare and contrast viruses and prions. Include information about the structure and composition of these entities, as well as their impact on humans. 58 MHR Unit 1 Diversity of Living Things

10 SECTION 2.2 Comparing Bacteria and Archaea Prokaryotes are represented by two domains: Bacteria and Archaea. Remember, by being considered in separate domains, biologists are saying that the two groups are more different from each other than any two groups within a domain. In other words, bacteria and archaea are more different from each other than an apple tree is from a blue whale, two organisms within the same domain, Eukarya. The domain Bacteria contains the kingdom Bacteria. Similarly, the domain Archaea contains the kingdom Archaea. Key Terms Comparing Morphology extremophile The most common forms in both bacteria and archaea are spheres and rods. The spherical forms are known as cocci (singular coccus), and the rod forms are called bacilli (singular bacillus). A third form present in both is a spiral shape. These three forms are shown in Figure 2.5. In addition, there are forms that do not fit into these three types. For example, some bacteria are shaped like cubes, pyramids, and rods with star-shaped cross sections. Some archaea are shaped like plates and rectangular rods, and a few species without cell walls have changeable shapes. A Magnification: 4000 B Magnification: C Magnification: 6000 Figure 2.5 There are three common shapes of prokaryotes: (A) cocci (spherical), (B) bacilli (rod-shaped), and (C) spiral shaped. Aggregations: Cells Grouped Together Even though all prokaryotes are unicellular, both domains have members that form aggregations, in which individual cells group together. Streptococcus bacteria are found in chains of spheres. Streptobacillus are rod-shaped bacteria that form similar chains. In the Anabaena, shown in Figure 2.6, the cells in the chains have different functions. Most of the cells carry out photosynthesis, but a few cells convert nitrogen from the environment into forms that are usable by other organisms. bacterium archaeon coccus bacillus methanogenesis mesophile binary fission conjugation endospore Gram stain bacterium (plural bacteria) an individual prokaryotic cell or a single species that is in the domain Bacteria archaeon (plural archaea) an individual prokaryotic cell or a single species that is in the domain Archaea coccus (plural cocci) a micro-organism whose overall morphology is spherical or nearly so bacillus (plural bacilli) a micro-organism whose overall morphology is rod-shaped Magnification: 275 Figure 2.6 Anabaena is a bacterium that forms colonies in long chains. Two different cell types in the chain can have different functions, each of which helps the other cell type. Chapter 2 Diversity: From Simple to Complex MHR 59

11 Comparing Nutrition methanogenesis a biological (or chemical) process that produces methane as an by-product There are many ways in which species in Archaea and Bacteria obtain energy. Some carry out photosynthesis, some consume other organisms, and still others get energy from various inorganic compounds such as hydrogen sulfide or iron. One metabolism that appears to be unique to the Archaea is methanogenesis, which produces methane gas as a by-product. Methane (CH4) is the simplest organic compound. It is a useful fuel and a potent greenhouse gas. Methanogenesis is an anaerobic process that occurs in environments that lack oxygen, and it is often one of the final stages of decomposition. Methane-producing archaea live in the digestive tracts of animals such as the cattle shown in Figure 2.7, making these animals a source of methane gas. Figure 2.7 The large mammals used in modern agriculture, including cattle and sheep, have digestive tracts that contain millions of methane-producing archaea. Each animal belches large quantities of methane every day. Explain how livestock farming might play a role in climate change, given that methane is a more potent greenhouse gas than carbon dioxide. Another key difference between Archaea and Bacteria is photosynthesis. Some bacteria are photosynthetic the best known of these are called cyanobacteria. An example of a cyanobacterium is shown in Figure 2.8. Like green plants, cyanobacteria use solar energy to convert carbon dioxide and water into sugar. In the process they produce oxygen. These bacteria are abundant in both fresh and salt water, and they account for much of the atmospheric oxygen on Earth. Some archaea use the energy in sunlight as a source of metabolic energy, but researchers are still seeking reliable evidence of photosynthesis in archaea. Figure 2.8 Cyanobacteria, such as Spirulina platensis, contain chlorophyll and carry out photosynthesis. Magnification: MHR Unit 1 Diversity of Living Things

12 Comparing Habitats Because of the diversity of ways in which bacteria and archaea obtain nutrients, these organisms are able to occupy a diverse array of habitats. When the term habitat is used for multicellular organisms, you might think of larger scales, such as freshwater marshes, coniferous forests, or dry grasslands. For prokaryotes, habitats on smaller scales must also be considered. Both archaea and bacteria occupy environments with oxygen (aerobic) and without oxygen (anaerobic). Methanogenic archaea, for instance, are abundant in the anaerobic depths of landfill sites, the guts of cattle, and sediments of swamps. Anaerobic bacteria are found in the human gut and many other environments. One of the most fascinating things about archaea is their ability to live in extreme environments. For this reason, they are referred to as extremophiles. Table 2.2 shows some of the extreme habitats in which different archaea are able to survive. Most bacteria are mesophiles organisms that occupy environments with moderate (less extreme) conditions. There are, however, extremophilic bacteria. And, as our knowledge of archaea accumulates, there are proving to be many mesophilic members of that domain too. The extremophilic capacities of prokaryotes have influenced scientists who are interested in extraterrestrial life. Scientists now know that life is possible in a much greater range of conditions than the eukaryotic world had suggested. extremophile an organism that lives in habitats characterized by extreme conditions mesophile an organism that lives in habitats characterized by moderate conditions Table 2.2 Habitats of Extremophiles Habitat Example Type of Extremophile Deep Sea Vents and Hot Springs Both of these habitats have extreme temperatures of over 100 C. The archaea that live around deep sea vents not only live with extreme temperatures, but in the absence of sunlight as well. The hot springs in Yellowstone National Park in the United States are home to several different species of archaea. Thermophile ( heat-lover ) The most heat-tolerant species known is in the genus Methanopyrus. Individuals live near deep sea vents in temperatures as high as 120 C, which is much higher than the boiling point of water. Volcanic Crater Lakes and Mine Drainage Lakes These habitats are extremely acidic, with a ph of less than 3. Sulfur from geothermal activity creates the acidic conditions of lakes in the craters of volcanoes. Mine drainage lakes are human-made; they result from mining operations. Acidophile ( acid-lover ) Picrophilus can live at a ph of 0, which is the acidity of car battery acid. Salt Lakes and Inland Seas Salt lakes, such as the Great Salt Lake, and inland seas, such as the Dead Sea, can have concentrations of salt higher than 20 percent. The Dead Sea, which has a high rate of evaporation, has a salt concentration of about 35 percent. Ocean water has a salt concentration of about 3.5 percent. Halophile ( salt-lover ) When the concentration of salt in water exceeds 20 percent, only halophilic archaea, such as Halococcus, can thrive. Some live in concentrations as high as 37 percent salt. Chapter 2 Diversity: From Simple to Complex MHR 61

13 Learning Check 7. Identify the three common forms of bacteria and archaea. 8. Which type of bacteria are photosynthetic? 9. Briefly describe the following types of archaea: thermophile, halophile, and acidophile. 10. What are some possible advantages to being a mesophile? 11. Compare and contrast methanogenesis and photosynthesis. 12. Would you consider an aggregation of Steptobacillus bacteria to be a multicellular organism? Explain your reasoning. binary fission the asexual form of reproduction used by most prokaryotes (and some eukaryotic organelles), in which a cell divides into two genetically identical cells (or organelles) Comparing Reproduction Since bacteria and archaea lack nuclei, they do not reproduce by mitosis or meiosis. Recall that the genetic material in prokaryotes is contained in a single chromosome within the cell. Prokaryotes reproduce through the asexual process of binary fission, shown in Figure 2.9. In binary fission, as a cell grows, it makes a copy of its original, single chromosome. When the cell reaches a certain size, it elongates, separating the original chromosome and its copy. The cell then builds a partition between them, called a septum, and eventually the original cell splits into two smaller, genetically identical cells. A cell elongates chromosome cell wall plasma membrane cytoplasm B septum begins to form septum forming C septum complete, distinct walls form septum complete Magnification: 5000 D cells separate Figure 2.9 Cell division in prokaryotes occurs by binary fission. In favourable conditions, a prokaryotic cell can grow and divide in as little as 20 minutes. Each new cell can then grow and produce two more cells 20 minutes later. A sequence of repeated doubling like this allows bacteria to produce huge populations in a fairly short time. 62 MHR Unit 1 Diversity of Living Things

14 Conjugation: New Genetic Content In less favourable conditions, some bacteria and archaea are able to exchange DNA by conjugation. This process produces cells with new genetic combinations, and thereby provides a chance that some may be better adapted to changing conditions. During conjugation, one cell links to another cell through a bridging structure and transfers all or part of its chromosomes to the other cell, as shown in Figure Unlike asexual reproduction, conjugation results in cells with new genetic content. The receiving cell then undergoes binary fission to produce more cells with the same genetic make-up. conjugation a process in which there is a transfer of genetic material involving two cells Figure 2.10 Genetic material being transferred through a long, tube-like pilus. Predict how conjugation could be an agent for increasing biodiversity among prokaryotic species that use it. Magnification: Plasmids: Small Loops of DNA In most bacteria and archaea, the chromosome is not the only part of the cell that contains genes. Plasmids are small loops of DNA that are separate from the main chromosome and that contain genes. These genes are different from those found in the chromosome. Plasmids can split from the chromosome and rejoin it. Plasmids may be transferred from one cell to another during conjugation. This makes plasmids an important means of genetic recombination in prokaryotes. Endospores: Protecting Genetic Material When environmental conditions threaten survival, some species of bacteria can form endospores like the one shown in Figure Endospores are hard-walled structures that protect and store the organism s genetic material. Endospores are resistant to high temperatures, drying out, freezing, radiation, and toxic chemicals. When suitable conditions return, the endospore germinates back into an active bacterium. So far, endospores have not been found in archaea. endospore a dormant bacterial cell able to survive for long periods during extreme conditions Magnification: 1500 Figure 2.11 In life-threatening conditions, certain species of bacteria form endospores that enable them to remain dormant (inactive) for periods of time that range from weeks to thousands of years. Chapter 2 Diversity: From Simple to Complex MHR 63

15 Gram stain a stain that separates bacteria into two major divisions (Gram positive and Gram negative) based on the cell wall s response to the stain Classifying and Identifying Bacteria and Archaea The biological species concept that uses sexual reproduction in its definition is of no use for the asexual bacteria and archaea. Instead, biologists have traditionally used a variety of means to identify and classify these species. One method developed in the 19th century but still in use is the Gram stain, shown in Figure This technique divides bacteria into two groups. Gram-positive bacteria have a thick protein layer on their cell wall and stain purple. Gram-negative bacteria have a thin protein layer on their cell wall and stain pink. Other stains are used to identify other groups, but none is as widely used as the Gram stain. Other methods traditionally used to identify and classify prokaryotes include size and shape, nutrition, movement, and genetic components. However, modern biologists prefer techniques that rely on DNA comparisons. A B Magnification: 700 Magnification: 700 Figure 2.12 The Gram stain divides most bacteria into two groups: Gram-positive (A) and Gramnegative. (B) The Gram-negative group of bacteria are larger in number and have more diverse species than the Gram-positive group. Activity 2.2 Classifying Bacteria Bacteria can be classified into two groups, Gram-negative and Gram-positive, based on the structure of their cell walls. In this activity, you will observe and classify several bacteria. Materials oil light microscope prepared slides of bacteria, numbered 1 to 4 Procedure 1. Observe slide 1 using the oil immersion lens. 2. Identify and record the shape of the bacterial cells. 3. Look at the cell walls of an individual bacterium and record the colour of the stained cell walls. 4. Repeat steps 1 to 3 for each of the remaining slides. Questions 1. Which of the slides contained Gram-negative bacteria? Which contained Gram-positive bacteria? Explain your reasoning. 2. Identify other differences among the bacteria you observed. Choose one difference and explain how it could be used to classify bacteria. 3. Doctors sometimes take a throat swab to obtain a sample of bacteria when patients have a sore throat. Describe two things that the sample can show to help the doctor diagnose a patient s illness. 64 MHR Unit 1 Diversity of Living Things

16 Bacteria and Human Health Food spoilage and the spread of disease are the result of bacteria carrying out their normal life functions. For example, botulism is a type of food poisoning caused by the species of anaerobic bacteria shown in Figure 2.13 (A) Clostridium botulinum. Commonly found in the soil, Clostridium botulinum forms endospores that are very resistant to heat and that germinate in anaerobic conditions. The metabolism of these bacteria produces toxic products that can cause nausea or even death in humans. The bacteria are not dangerous, however, unless they are trapped with food for a period of time under anaerobic conditions. This sometimes occurs when people can, or seal, food into bottles or jars at home without proper care. To ensure that bacterial endospores are killed, the food must be heated under high pressure at temperatures above the boiling point of water. If you have ever had strep throat, an ear infection, or a cavity in your tooth, then you have experienced a disease caused by bacteria. The bacteria that cause some of these diseases are shown in Figure A B C Magnification: Magnification: 4100 Magnification: 5300 Figure 2.13 (A) Clostridium botulinum is an anaerobic bacterium that can cause illness in humans. (B) Streptococcus pyogenes is a Gram-positive bacterium that causes strep throat infections. (C) Streptococcus mutans is a Gram-positive bacterium that causes tooth decay. Bacteria and the Environment As decomposers, bacteria break down organic materials and release carbon, hydrogen, and other elements into the environment for use by other organisms. Nutrient cycles such as the carbon, nitrogen, and sulfur cycles depend on the fact that chemicals excreted into the environment by one type of organism can be used as nutrients by another type. These links join together different types of bacteria into microscopic food webs. Cyanobacteria are major producers of oxygen through the process of photosynthesis. They were probably among the first organisms on Earth to carry out this process. Two billion years ago, Earth s atmosphere had little or no oxygen. By releasing oxygen as a product of photosynthesis, bacteria altered the composition of the atmosphere and literally changed the world. Other species of cyanobacteria are the only organisms able to convert atmospheric nitrogen into a form that is usable by most organisms. Archaea and Biotechnology Enzymes that are unique to archaea allow these organisms to live under extreme conditions of heat, cold, acidity, and salinity. Biotechnology and industry depend on the use of enzymes for many processes, including DNA analysis and diagnosing diseases. While most enzymes break down and stop working when they are exposed to extreme conditions, archaeon enzymes do not. For example, polymerase chain reaction, or PCR, is a technology that can produce millions of copies of a DNA sequence. PCR used to be a slow and expensive process because standard enzymes were destroyed by high temperatures during the process and had to be replaced by hand each time. But the DNA polymerase from archaea can withstand these high temperatures, and the PCR process is now fully automated. This revolutionary technology has become commonplace. Chapter 2 Diversity: From Simple to Complex MHR 65

17 Section 2.2 REVIEW Section Summary The two domains into which prokaryotes are classified are Bacteria and Archaea. Each of these domains has a kingdom by the same name. Bacteria and archaea have three basic shapes cocci, bacilli, and spiral. A major group of archaea are methanogens that produce methane. A major group of bacteria are cyanobacteria that use photosynthesis. Extremophiles occupy habitats of extreme conditions, and most are archaea. Mesophiles occupy habitats that have moderate conditions. Most bacteria are mesophiles. Prokaryotes reproduce asexually through binary fission. They can exchange DNA through the process of conjugation. Prokaryotes were once classified by shape and responses to stains, but modern taxonomists use DNA sequences. Review Questions 1. C Make a table that identifies and describes the three common shapes for bacteria and archaea. Draw an example organism for each shape. 2. K/U Which of the following statements are true of prokaryotes? Explain your answers. a. They include both bacteria and archaea. b. They do not cause disease in humans. c. They are only found in extremely hot environments. d. All are parasitic. 3. K/U Why is being able to form endospores advantageous? 4. K/U Scientists use several characteristics to classify prokaryotes. a. Explain how the Gram stain is used to classify bacteria. b. What is the modern approach to classification of prokaryotes? 5. A The image shows the cross sections of two cell walls. Based on what you know about the Gram stain, which do you think is the cell wall of a Gram-positive bacterium and which is that of the Gram-negative one? Why? cell wall with thin layer of protein cell wall with thick layer of protein cytoplasm cytoplasm outer membrane cell membrane 6. C Use a flowchart to show the sequence the steps involved in conjugation. 7. T/I Home-preserved fruit is more likely to be a source of food poisoning caused by Clostridium botulinum than fresh fruit. Infer why. 8. K/U The images below show a bacterial cell dividing into two cells. The sequence of cell division is incorrect. Redraw the illustrations in the correct sequence, and explain what is happening at each step. 9. A Of all types of agriculture, intensive livestock operations (feedlots) are the most damaging in terms of greenhouse gas emissions. Explain this statement in terms of metabolism of some species of the kingdom Archaea. 10. T/I Predict what Earth s atmosphere might be like today had cyanobacteria not appeared some two to three billion years ago. 11. A Our intestinal tract is filled with an enormous number of helpful bacteria called probiotic bacteria. Probiotic bacteria inhibit the growth of disease-causing bacteria, particularly those responsible for gastrointestinal infections. Predict the possible effects of the overuse of antibiotics on probiotic bacteria living in our digestive system and the possible consequences to an individual. 12. A An expedition to Iceland s hot springs has yielded new strains of bacteria. These bacteria may be able to produce hydrogen and ethanol fuels from wastewater that is discharged from factories processing sugar beets, potatoes, and other plant material. What would be the advantages of this type of practice? 66 MHR Unit 1 Diversity of Living Things

18 SECTION 2.3 Eukaryotic Evolution and Diversity For about 1.5 billion years, prokaryotes were the only organisms on Earth. From about 3.5 to 2 billion years ago, prokaryotic organisms thrived in many different ecosystems, some carrying out photosynthesis while others survived in extreme environments without light. Today, prokaryotes are still widespread throughout Earth s ecosystems and thrive in a diversity of ways. However, they now live in the presence of many other types of organisms that are larger and more complex than they are. About 2 billion years ago, eukaryotes evolved, which led to an increase in the diversity of life on Earth. Eukaryotic organisms are more complex than prokaryotes. Eukaryotes usually have far more genes than prokaryotes, allowing for greater cellular diversity in terms of size, shape, mobility, and specialized functions. For example, the single cell that represents the start of a human being contains instructions for countless cell divisions that ultimately produce an organism of trillions of cells. Today scientists continue to collect data and examine evidence to answer an important question: How did eukaryotic organisms develop? Endosymbiosis One of the main theories about the origin of eukaryotic organisms is that the eukaryotic cell represents the merger of two or more simpler cells, possibly prokaryote-like ones. This is known as endosymbiosis, which is shown in Figure In endosymbiosis, one cell engulfs a different type of cell. However, the engulfed cell survives and becomes an internal part of the engulfing cell. Recall that prokaryotes lack many internal structures and the only membrane is the one that surrounds the cell. In contrast, eukaryote structure is internally complex, with multiple, membrane-bound organelles. It is believed that these organelles are the ancestors of once free-living prokaryotes. Two eukaryotic organelles present the strongest evidence of endosymbiosis in early eukaryotes. One is the chloroplast, an organelle found in photosynthetic eukaryotes that converts solar energy into sugar. The other is the mitochondrion, an organelle that does the opposite it extracts energy stored in sugar so that the cell can do work. Key Terms endosymbiosis endosymbiont host cell endosymbiosis theory that explains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells aerobic bacterium nucleus endoplasmic reticulum cyanobacterium cell has a nucleus and other organelles cell has mitochondria cell has chloroplasts Figure 2.14 A likely event in the evolution of the eukaryotic cell was the endosymbiotic engulfing of smaller cells that became part of the larger one. Chapter 2 Diversity: From Simple to Complex MHR 67

19 endosymbiont a cell that is engulfed by another cell in endosymbiosis host cell a cell that engulfs another cell in endosymbiosis Chloroplasts and Mitochondria The theory of endosymbiosis suggests that mitochondria and chloroplasts were once small, free-living prokaryotes. In separate events during evolutionary history, they were engulfed by other, larger cells. Rather than being digested, they remained intact. They continued to do inside these cells what they had previously done outside convert solar energy into molecular energy in the case of the chloroplast, and convert molecular energy into work in the case of the mitochondrion. The organelle is called an endosymbiont and the engulfing cell is a host cell. This arrangement benefited the host cell by making it more energy efficient. There is much evidence supporting the endosymbiotic theory. The membranes of chloroplasts and mitochondria are similar to those of living prokaryotes. The ribosomes, structures used to assemble proteins, in these organelles are much more similar to prokaryotic ribosomes than to the ribosomes elsewhere in the eukaryotic cell. These organelles also reproduce by binary fission within the cell, as shown in Figure Finally, each contains a circular chromosome, and many of the gene sequences closely match those of living prokaryotes. Not surprisingly, the genes in the chloroplast most closely match the genes of modern cyanobacteria, the prokaryotes that are masters of photosynthesis. nucleoid mitochondrion Figure 2.15 Mitochondria have their own genetic material in a bacteria-like chromosome. Like bacteria, they also divide by binary fission. Explain how this genetic material and mode of reproduction support the endosymbiotic theory of eukaryotic evolution. 68 MHR Unit 1 Diversity of Living Things

20 Multicellularity Endosymbiosis may be responsible for the complex eukaryotic cell, but by itself it does not account for multicellularity, another eukaryotic advance. Recall that prokaryotes sometimes form aggregations, such as chains. Generally, the cells in prokaryotic aggregations carry out the same function, without specialization. In addition, these aggregations are considered to be collections of individuals, not one individual, although they are often clones of each other. After eukaryotes appeared on Earth, a great variety of unicellular forms evolved, but multicellular forms came later. Biologists use a range of evidence to estimate that the first multicellular organisms existed 1.2 to 1.5 billion years ago, so they have existed on Earth less than half as long as unicellular organisms. The oldest such fossils are of red algae found in rocks in arctic Canada, shown in Figure These were still simple organisms by modern standards. Based on fossil evidence, scientists think that large, complex eukaryotes first developed about 550 million years ago. Figure 2.16 Ancient sedimentary rocks of arctic Canada have provided fossils that are clues to the evolution of multicellularity and sexual reproduction in eukaryotes. Scientists hypothesize that the first multicellular organisms arose from colonies created by dividing individual cells. Genes within these cells contained instructions for some of the cells to become specialized for different functions. With the passage of thousands of years, increasing specialization made it possible for different functions to develop among different groupings of cells in multicellular organisms. For example, some groups of cells became specialized to absorb nutrients, while others became specialized to gather information from the environment. Learning Check 13. List several ways in which eukaryotic organisms can be considered more complex than prokaryotic ones. 14. What is endosymbiosis? How is it related to the evolution of eukaryotic cells? 15. In point form, list the evidence that supports the endosymbiotic theory. 16. Which group of organisms have gene sequences most similar to the genes found in the circular chromosome in chloroplasts? Explain why. 17. How do prokaryotic aggregations and multicellular eukaryotic organisms differ, given that they are both made of multiple cells? 18. Make a timeline showing the major dates in the evolution of large, complex eukaryotes. Chapter 2 Diversity: From Simple to Complex MHR 69

21 Life Cycles and Reproduction Not only are eukaryotes more structurally diverse than prokaryotes, but they have more reproductive diversity as well. In prokaryotes, cell division and reproduction are usually the same process: asexual reproduction. In unicellular eukaryotes, this is also the case sometimes. However, in most eukaryotes, even unicellular ones, things are more complicated. Some use more complicated methods of asexual reproduction, such as multiple fission, in which there are multiple copies made of a cell more or less at one time. More significantly, especially in multicellular individuals, cell division is not the same as reproduction at the level of the individual. For example, in humans, individual cells are being reproduced all the time. However, reproduction of individual organisms is through sexual reproduction. Sexual reproduction is common among eukaryotes. In sexual reproduction, two individuals make eggs and sperm, known as gametes, which are haploid. Haploid cells contain only one set of chromosomes, compared to the two sets of chromosomes in other cells. When an egg and a sperm cell fuse, they form a zygote, a cell that is diploid. A diploid cell contains two sets of chromosomes, one set inherited from each parent cell. Sexual reproduction is not possible without meiosis, which is unique to eukaryotes. You will learn more about meiosis in Chapter 4. Figure 2.17 compares asexual and sexual life cycles among organisms. Sexual life cycles vary, but there are features that are common to all. Most importantly, organisms that reproduce through sexual reproduction alternate between meiosis, which makes sperm and eggs, and fertilization, which merges sperm and egg. What varies among organisms is the timing of these two events. os is asexual reproductive structures m it Asexual Life Cycle os is haploid or diploid organism t mi Sexual Life Cycle Gametic Zygotic Sporic mitosis haploid stage organism mitosis mitosis gametes diploid diploid stage organism mi to s i s n tio iza til zygote n tio iza til n tio iza til zygote diploid r fe r fe r fe to s i s mitosis haploid haploid diploid mi is os haploid diploid organism ei m is os ei m is os ei m gametes spores haploid organism spores zygote gamete Figure 2.17 Life cycles can be asexual or sexual. 70 MHR Unit 1 Diversity of Living Things

22 Section 2.3 REVIEW Section Summary Scientists hypothesize that eukaryotic cells developed in the past through endosymbiosis. The two organelles that present the strongest evidence of endosymbiosis are chloroplasts and mitochondria. In eukaryotes, sexual life cycles vary, but they alternate between meiosis, which produces haploid cells, and fertilization, which produces diploid cells. Review Questions 1. K/U What is the advantage of a eukaryotic cell having more genes than a prokaryotic cell? 2. C Write a short paragraph persuading the reader to accept the endosymbiosis hypothesis. 3. C Draw the hypothesized sequence of events of endosymbiosis leading to the development of a plant cell. 4. T/I Nearly all eukaryotic cells contain mitochondria, but only some, such as plants and some protists, contain chloroplasts as well. Which endosymbiotic event do you think came first, engulfing a cyanobacterium that became a chloroplast or engulfing a heterotrophic bacterium that became a mitochondrion? Explain your reasoning. 5. K/U What is the main difference between the gametic and the zygotic life cycles shown in Figure 2.17? 6. A Use the illustration below to explain the possible evolution of the eukaryotic animal cell. primitive prokaryote early bacteria ancestral eukaryote aerobic bacteria 7. C Copy the cell that represents the ancestral eukaryote in the diagram above into your notebook. Label the diagram to identify the endosymbiont and the host cell. 8. K/U Explain how mitochondria reproduce. 9. K/U How do scientists think that multicellular eukaryotes arose? 10. A Relate the idea of groups of specialized cells in multicellular organisms to three functions in the human body. 11. K/U What is the main difference in reproduction between prokaryotes and eukaryotes? 12. C Use a Venn diagram to compare and contrast a gamete and a zygote. 13. A Refer to Figure Identify whether the life cycle of the organisms described below is asexual or sexual. For those that you have identified as sexual life cycles, determine if they are gametic, zygotic, or sporic. a. Sea lettuce (Ulva) has two life stages. In stage 1, a zygote undergoes meiosis and releases swimming, haploid spores. These spores grow into male and female haploid organisms. In stage 2, the haploid organisms undergo mitosis to produce mobile male and female gametes. The gametes fuse together and swim to the bottom, where they grow into the zygote once more. b. Plants have a diploid stage, in which cells undergoing meiosis produce haploid reproductive cells called spores. The spores develop into haploid organisms that produce haploid gametes by mitosis. The gametes unite to produce a diploid zygote that grows into a diploid stage organism, thus completing the cycle. c. Paramecia are unicellular organisms belonging to the kingdom Protista. Under normal circumstances, paramecia reproduce by splitting themselves down the middle, with each new paramecium receiving half of the organelles. This process is called binary fission. d. A fertilized egg of a fish is called a zygote. The diploid zygote uses mitosis to develop into an adult diploid organism. Specialized cells in the reproductive organs of the adults undergo meiosis to create haploid gametes. When the adult fish spawn, the sperm from the male fertilize the eggs released by the female to form the diploid zygote. Chapter 2 Diversity: From Simple to Complex MHR 71

23 SECTION Protists: The Unicellular Eukaryotes 2.4 A drop of pond water under a light microscope can reveal a great diversity of life that is invisible to the unaided eye. Single-celled organisms with a variety of shapes and colours move about using long whips or numerous tiny moving hairs spinning, lurching, reversing, and investigating their environment. Compared to the prokaryotic cells visible only under higher power, these protists are large, diversely shaped, and captivating to watch. Key Terms protist parasite pseudopod cilium flagellum red tide Characteristics of Protists Most protists are unicellular. They are grouped as protists mainly because they do not fit into the other kingdoms, rather than because they are similar or closely related to one another. One group of protists that biologists do not agree on is the multicellular algae. This group of organisms can be divided into distinct groups (red, green, and brown algae). However, some taxonomists place them in the plant kingdom, others in the protist kingdom, and still others consider the red and green algae as plants but the brown algae as protists. In this textbook, the multicellular algae and their relationship with plants will be discussed in Chapter 3. Chapter 2 restricts the survey of protists to the three groups of unicellular eukaryotes shown in Table 2.3. These three groups are based on the method of obtaining nutrition. protist a eukaryotic organism, usually unicellular, that is not a fungus, plant, or animal Table 2.3 Unicellular Protists Animal-like Protists (Protozoans) Group Amoebas, ciliates (shown below), and flagellates Example Distinguishing characteristics Fungus-like Protists Slime moulds (shown below) and water moulds Magnification: 180 They are animal-like because they consume other organisms for food. Some species are parasites. parasite an organism that benefits by living in or on another organism at the expense of that organism Plant-like Protists Euglenoids, diatoms (shown below), and dinoflagellates Magnification: unavailable They are fungus-like because they absorb nutrients from other organisms, living or dead. Some slime moulds consume other organisms. Some water moulds are parasites. They are plant-like because they make their own food by photosynthesis. Some consume other organisms when light is unavailable. Some live as symbionts within other organisms. Animal-like Protists The animal-like protists, often called protozoans, are heterotrophs. They commonly consume other organisms for food, especially prokaryotes and other protozoans, or organic wastes. A number of species are parasites, taking nutrients from the organisms in which they reside. 72 MHR Unit 1 Diversity of Living Things

24 The Cercozoans: Phylum Cercozoa The most familiar of the cercozoans are the amoebas. Their surface is a cell membrane without a cell wall. This means they change shape, using their internal cytoskeleton to move and create different forms. Temporary extensions of the cytoplasm that are created this way are called pseudopods ( false feet ). Pseudopods are used for both feeding and locomotion, as shown in Figure pseudopodia pseudopod (plural pseudopodia) a temporary cytoplasmic extension that amoebas use for feeding and movement cytoplasm nucleus food vacuole contractile vacuole Figure 2.18 When amoebas detect food, they form pseudopods from the cell membrane and engulf the target. Amoebas live in salt water, fresh water, and mud, and a few are parasites living inside an animal host. For example, Entamoeba hystolitica feeds on the lining of the small intestine in humans and causes a serious illness called amoebic dysentery. Many other species of intestinal amoeba also live inside humans without causing significant problems. Intestinal amoebas can be spread by drinking contaminated water or by eating produce that has been contaminated. The Ciliates: Phylum Ciliophora Ciliates, such as the one in Figure 2.19, have many short, hair-like projections that cover the surface of the cell. These hair-like projections are called cilia (singular cilium). Cilia have a dual purpose locomotion and sweeping food particles along the cell surface to move them into the cell. Some of the best-known ciliates are in the genus Paramecium, and are known as paramecia. Many species of ciliates are large and complex, growing to over 100 μm in length. As with the other groups of protozoans, some members are free-living, like paramecia, and some are parasites. Only one species of ciliate is known to be a parasite of humans Balantidium coli lives in the large intestine and causes diarrhea. cilium (plural cilia) a short, hair-like projection that functions in cell movement and particle manipulation when coordinated with other cilia Oral groove and gullet The action of cilia moves food down the oral groove into the gullet. Cilia The cell is covered by thousands of tiny hair-like cilia. Figure 2.19 Paramecia use cilia to move through the water and to move food into the gullet. Food vacuole The food vacuole, where the meal is digested, forms at the end of the gullet. Chapter 2 Diversity: From Simple to Complex MHR 73

25 flagellum (plural flagella) a long, hair-like projection extending from the cell membrane that propels the cell using a whip-like motion Magnification: 90 Figure 2.20 Members of the genus Trichonympha have a mutualistic relationship with termites. Flagellates: Phylum Zoomastigina Protists in this phylum are called flagellates because they have one or more flagella that whip from side to side to move them about. Flagellates have a hard protective covering over their outer membrane. Some species are free-living, some are parasites, and some live in mutualistic relationships. Recall that in mutualistic relationships, both organisms benefit from the relationship. Some examples of mutualistic flagellates include many species that live in the digestive tract of animals and help the host animals digest plant material. For example, termites feed on wood, but they are unable to digest the tough cellulose that makes up a large part of their diet. Flagellates, like the one shown in Figure 2.20, live in termite intestines and produce enzymes that convert cellulose to sugars, which the termites can use. In return, the flagellates receive a steady supply of food and a warm and protected environment. The Sporozoans: Phylum Sporozoa Sporozoans are parasites of animals, taking the nutrients they need from their hosts. Most members of this group have life cycles that alternate between sexual and asexual reproduction and often alternate between two hosts. Protists in the genus Plasmodium cause malaria in humans. Figure 2.21 shows how these protists are transferred to humans from mosquitoes. Up to two million people die annually from malaria. A A mosquito feeds on an infected person. It ingests reproductive cells of Plasmodium present in red blood cells. B The reproductive cells fuse inside the mosquito to form a zygote. The zygote divides many times to form numerous spore-like cell fragments. Eventually, the zygote breaks open, releasing cells called sporozoites. gametes zygote gut wall of mosquito C The sporozoites invade the mosquito s salivary gland, from where they will be injected into a new host when the mosquito bites again. sporozoites human host E The blood cells rupture, releasing toxic substances and great numbers of spores. These spores go on to infect more red blood cells. D Inside the human host, the sporozoites reproduce asexually in the liver to form a second type of spore-like cell. From the liver, these new spores enter the bloodstream, invade red blood cells, and multiply rapidly inside them. Figure 2.21 The life cycle of the malaria-causing protist Plasmodium involves two hosts, a mosquito and a human. Symptoms of malaria include high fever, chills, nausea, and vomiting. Explain what happens to sporozoites when they enter a human liver. 74 MHR Unit 1 Diversity of Living Things

26 Fungus-like Protists The members of this group are heterotrophs, but instead of ingesting other organisms, they absorb nutrients from living organisms, dead organisms, and wastes. Like fungi, fungus-like protists produce spores. However, they differ from fungi at the cellular level. For example, the cell wall of fungus-like protists is different from the cell wall of fungi. Some examples of fungus-like protists include slime moulds and water moulds, as shown in Table 2.4. Slime moulds are divided into two main groups: plasmodial slime moulds and cellular slime moulds. Table 2.4 Fungus-like Protists Type Description Example Plasmodial slime moulds: Phylum Myxomycota Plasmodial slime moulds are visible to the unaided eye as tiny slug-like organisms that creep over damp, decaying plant material in forests and fields. This streaming blob, called a plasmodium, contains many nuclei. Like amoebas, these slime moulds feed by engulfing small particles of food into their cytoplasm. Some of the cytoplasm is concentrated to form a skeleton-like structure through which the liquid cytoplasm flows. Cellular slime moulds: Phylum Acrasiomycota Water moulds: Phylum Oomycota Cellular slime moulds exist as individual amoeboid cells with one nucleus each. Like protozoans, each cell feeds by ingesting tiny bacteria or yeast cells. When food becomes scarce, the cells release a chemical that causes them to gather together to form a pseudoplasmodium. Despite their names and similarities, there is no strong evidence that the two types of slime moulds are closely related. Water moulds are filamentous organisms that resemble fungi. Most live on dead organic matter. Some species, however, are parasites on fish, insects, and plants. They extend fungus-like threads into their host s tissues, where they release digestive enzymes and absorb the resulting nutrients. Activity 2.3 Slime Moulds: Science, Technology, Society, and the Environment Would it surprise you to know that scientists use slime moulds in cancer research, or to learn more about diseases such as Alzheimer s disease? Or that, through the Planetary Biodiversity Inventory (PBI), scientists are studying the worldwide distribution of slime moulds and trying to complete a worldwide inventory of slime mould species? Although it may not seem like it, slime moulds can have an interesting and important impact on technology, society, and the environment. Procedure 1. Choose one of the following topics about slime moulds to research. Or, you could choose your own topic. Slime Mould Physarum polycephalum: Used to Solve Traffic Jams? Phytophthora infestans and the Irish Potato Famine Alien Invasion: Fuligo septica (Common Name: Dog Vomit Slime Mould) Slime Moulds Form Hirano Bodies: Used in Alzheimer s Research 2. Use the Internet to research information about your topic. Questions 1. Answer the following questions as you complete your research: a. What is the story behind the topic? b. What, if any, research is being conducted on this topic? c. How does this topic impact technology, society, or the environment? 2. Prepare a short presentation of your topic to share with the class. Consider questions your audience may ask about the topic as you prepare your presentation. Chapter 2 Diversity: From Simple to Complex MHR 75

27 Learning Check 19. Most organisms are grouped together because they are similar or closely related to each other. How does the grouping of protists by taxonomists differ from this? 20. What is the function of a pseudopod? 21. Use a Venn diagram to compare and contrast cilia and flagella. 22. Compare and contrast plasmodial slime moulds and cellular slime moulds. 23. Give two examples of protists that are parasites and the problems they cause their host. 24. Interpret the following statement for a Grade 6 student. Many scientists use the word protozoan to refer to a eukaryotic, unicellular, heterotrophic protist, such as an amoeba or a ciliate. Plant-like Protists Plant-like protists contain pigments in their chloroplasts to carry out photosynthesis. The most common of these pigments is chlorophyll, which gives many of them a green colour. Unicellular plant-like protists include diatoms, dinoflagellates, and euglenoids. Magnification: 125 Figure 2.22 The many species of diatoms have different shapes and sizes based on differences in their silica walls. Diatoms: Phylum Chrysophyta Phytoplankton are single-celled, free-floating aquatic organisms. Diatoms, shown in Figure 2.22, are among the most diverse and abundant phytoplankton and are an important source of food for larger marine organisms. Diatoms have rigid cell walls with an outer layer of silica, a common ingredient in sand and glass. The walls are made of two unequal parts, the smaller of which fits neatly inside the other, like a box with a lid. Most of the time, diatoms reproduce asexually by mitosis. Sexual reproduction is less common and occurs under unfavourable environmental conditions. The reproductive cycle of diatoms is shown in Figure mitosis SuggestedInvestigation Inquiry Investigation 2-B, Sampling Pond Organisms mitosis wall formation around cell Asexual reproduction Sexual reproduction meiosis zygote gametes fusion of gametes sperm released Figure 2.23 Diatoms usually reproduce asexually, but under certain conditions they also reproduce sexually. Describe the steps involved in sexual reproduction of diatoms. 76 MHR Unit 1 Diversity of Living Things

28 Dinoflagellates: Phylum Pyrrophyta Like diatoms, most dinoflagellates are phytoplankton. A distinguishing feature of dinoflagellates is that they have two flagella at right angles to each other. As the flagella beat, a twirling motion is produced, so these organisms move by spinning through the water. Under conditions such as plentiful nutrients, dinoflagellates reproduce very quickly. The resulting population explosion is called a bloom or algal bloom. In species that have red photosynthetic pigments, the bloom is referred to as a red tide, an example of which is shown in Figure The species that form red tides produce a toxin that becomes concentrated in the tissues of plankton-eating shellfish. If humans eat those shellfish, they can become seriously ill or die. red tide a coastal phenomenon in which dinoflagellates that contain red pigments are so concentrated that the seawater has a distinct red colour Magnification: Figure 2.24 Dinoflagellates, such as Gonyaulax catenella, can cause red tides, in which many marine organisms can die and shellfish can become toxic. Some species of dinoflagellates live inside other organisms. The best known of these are the reef-building corals. Living inside many species of coral are dinoflagellates of the genus Symbiodinium. The protists benefit by using nitrogen wastes and carbon dioxide obtained by the coral, and the coral gains the benefits of photosynthesis, which is carried on by the protists. If ocean temperatures rise to abnormal levels, the coral-protist partnership breaks down and the protists are expelled in a process referred to as coral bleaching. Bleaching often results in the death of the corals. As Earth s climate has warmed in recent decades, more frequent incidences of dinoflagellates being expelled from corals have occurred. Permanent damage has resulted, including to Australia s Great Barrier Reef. When coral reefs are permanently damaged as a result of bleaching, other organisms that consume coral or live on the reef are also affected. Euglenoids There are over one thousand species of euglenoids, most of which are found in shallow fresh water. Although they have chloroplasts and conduct photosynthesis, they also have flagella and can absorb nutrients. With both plant-like and animal-like characteristics, euglenoids tend to be autotrophs in sunlight and heterotrophs in the dark. Euglenoids in the genus Euglena, such as the one shown in Figure 2.25, have a light-detecting structure called an eyespot. This light receptor does not create an image like the animal eye, but it does allow these protists to use their flagella to orient toward the light. Magnification: 300 Figure 2.25 Euglena gracilis are commonly found in slow-moving or standing water, such as ponds on or near agricultural fields. Chapter 2 Diversity: From Simple to Complex MHR 77

29 Section 2.4 REVIEW Section Summary Protists are generally divided into three groups based on how they obtain nutrition: animal-like protists, fungus-like protists, and plant-like protists. Animal-like protists are called protozoans and include amoebas and paramecia. Some protozoans, such as Entamoeba hystolitica and Balantidium coli, can cause intestinal infections in humans. Several types of sporozoans cause malaria in humans. Fungus-like protists include slime moulds and water moulds. Plant-like protists include diatoms, dinoflagellates, and euglenoids. Dinoflagellates can cause red tides when nutrients are plentiful. Review Questions 1. K/U Explain how the kingdom Protista is different from other kingdoms. 2. K/U List the three main groups in the kingdom Protista. What are their modes of nutrition? 3. C Use a graphic organizer to summarize the following information about protozoans: representative organisms, methods of locomotion, their relationships with other organisms, and how they affect an ecosystem. 4. K/U In what way do slime moulds resemble the following? a. fungi b. plants c. protists 5. A In coastal areas of Canada where shellfish are harvested for human consumption, local authorities monitor the populations of dinoflagellates in the water during harvest season. Why do they do this? 6. T/I During an ecology field trip, a group of students collected data about diatoms in a pond. They measured the number of cells in the water at various depths. They produced the graph below based on their data. Use the graph to answer the following questions. a. At what time were the highest concentrations of diatoms at the surface? b. At what time were the highest concentrations of diatoms below the surface? c. Why might the diatoms show the pattern shown in the graph? Location of Highest Concentration of Diatoms Surface 50 cm Locations of Diatoms 100 cm 12 A.M. 12 P.M. 12 A.M. 12 P.M. Time 7. A In the 1800s, malaria was a fairly common disease in parts of North America. One method for fighting the incidence of malaria was to eliminate swampy and marshy areas by filling them in with soil. a. What reasoning do you think was used to come up with this method? b. What are some possible negative consequences of using this method to reduce the incidence of malaria? 8. K/U Study the drawings below. Identify the phylum to which each organism belongs. Explain how you decided where each organism belongs. a. b. c. d. 9. C Make a concept map that relates the following terms: plant-like, protozoans, Entamoeba hystolitica, protists, fungus-like, water moulds, cercozoans, Euglena gracilis. 10. A Explain why it would be difficult to categorize a euglenoid protist as a producer or a consumer. 11. C Use Figure 2.23 to construct a graphic organizer summarizing the reproductive life cycle of a diatom. 12. K/U Identify two examples of protists that have mutualistic relationships with other organisms. Explain how each organism benefits from the relationship. 13. C Use a flow chart to sequence the events that can occur on a coral reef if water temperatures rise too high. In the last box, predict what could happen to organisms that consume coral or live on the reef. 78 MHR Unit 1 Diversity of Living Things