Darwin's Theory of Evolution: Unity and Diversity of Life, High school final essays of English

Download Darwin's Theory of Evolution: Unity and Diversity of Life and more High school final essays English in PDF only on Docsity! EVOLUTION: THE THEMES OF BIOLOGY AND SCIENTIFIC INQUIRY The study of life reveals common theme: Organization Information Energy and Matter Interactions Evolution THEME: New Properties Emerged at Successive Levels of Biological Organization The study of life extends from the global scale of the entire living planet to the microscopic scale of cells and molecules. Zooming in at ever-finer resolution illustrates an approach called reductionism, which reduces complex systems to simpler components that are more manageable to study. Reductionism is a powerful strategy in biology. 1 The Biosphere - It consists of all life on Earth and all the places where life exists: most regions of land, most bodies of water, the atmosphere to an _ altitude of several kilometers, and even sediments far below the ocean floor. 2 Ecosystems - An ecosystem consists of all the living things in a particular area, along with all the nonliving components of the environment with which life interacts, such as soil, water, atmospheric gases, and light. 3 Communities - The array of organisms inhabiting a particular ecosystem is called a biological community. 4 Populations - A population consists of all the individuals of a species living within the bounds of a specified area. 1 5 Organisms - Individual living things are called organisms. 6 Organs and Organ Systems - The organs of complex animals and plants are organized into organ systems, each a team of organs that cooperate in a larger function. Organs consist of multiple tissues. 7 Tissues - Each tissue is a group of cells that work together, performing a_ specialized function. 8 Cells - The cell is life's fundamental unit of structure and function. Some organisms are single cells, while others are multicellular. A single cell performs all the functions of life, while a multicellular organism has a division of labor among specialized cells. 9 Organelles - Chloroplasts are examples of organelles; the various functional components present in cells. 10 Molecule - A molecule is a chemical structure consisting of two or more units called atoms. Emergent Properties - These emergent properties are due to the arrangement and interactions of parts as complexity increases. ¢ To explore emergent properties more fully, biologists today complement reductionism —_ with systems biology (the dynamic behavior of an integrated network of components), the exploration of a biological system by analyzing the interactions among its parts. Structure and Function - At each level of the biological hierarchy, biologists find a correlation of structure and function. The Cell: An Organism's Basic Unit of Structure and Function The cell is the smallest unit of organization that can perform all activities required for life. In fact, the actions of organisms are all based on the functioning of cells. Theme: Life's Processes Involve Expression and Transmission of Genetic Information Within cells, structures called chromosomes contain genetic material in the form of DNA (deoxyribonucleic acid). DNA, the Genetic Material = Each time a cell divides, the DNA is first replicated, or copied, and each of the two cellular offspring inherits a complete set of chromosomes, identical to that of the parent cell. Each chromosome contains one very long DNA molecule with hundreds or thousands of genes, each a section of the DNA of the chromosome. =Transmitted from parents to offspring, genes are the units of inheritance. They encode the information necessary to build all of the molecules synthesized within a cell, which in turn establish that cell's identity and function Each of us began as a single cell stocked with DNA inherited from our parents. The replication of that DNA during each round of cell division transmitted copies of the DNA to what eventually became the trillions of cells of our body. As the cells grew and divided, the genetic information encoded by the DNA directed our development. The molecular structure of DNA accounts for its ability to store information. A DNA molecule is made up of two long chains, called strands, arranged in a double helix. Each chain is made up of four kinds of chemical building blocks called nucleotides, abbreviated A, T, C, and G. = Specific sequences of these four nucleotides encode the information in genes. = Many genes provide the blueprints for making proteins, which are the major players in building and maintaining the cell and carrying out its activities. = Genes control protein production indirectly, using a related molecule called RNA as an intermediary. The sequence of nucleotides along a gene is transcribed into RNA, which is then translated into a linked series of protein building blocks called amino acids. These two stages result in a specific protein with a unique shape and function. The entire process, by which the information in a gene directs the manufacture of a cellular product, is called gene expression. = Gene expression: The transfer of information from a gene results in a functional protein. =Genomics: Large-Scale Analysis of DNA Sequences - The entire “library” of genetic instructions that an organism inherits is called its genome. - It is study of a whole sets of genes (or other DNA) in one or more species. - Likewise, the term proteomics refers to the study of sets of proteins and their properties. The entire set of proteins expressed by a given cell or group of cells is called a proteome. the Origin of Species by Means of Natural Selection”. Darwin articulated two main points. 1. The first point was that contemporary species arose from a succession of ancestors that differed from them. Darwin called this process “descent with modification.” This insightful phrase captured the duality of life’s unity and diversity. 2. The second main point was his proposal that “natural selection" is an _— evolutionary mechanism for descent with modification Darwin's Theory of Evolution by Natural Selection 1. More individuals are produced each generation that can survive. 2. Phenotypic variation exists among individuals and the variation is heritable. 3. Those individuals with heritable traits better suited to the environment will survive. 4. When reproductive isolation occurs new species will form The Tree of Life Fossils and other evidence corroborate anatomical unity in supporting this view of mammalian descent from a common ancestor. Darwin proposed that natural selection, by its cumulative effects over long periods of time, could cause an ancestral species to give rise to two or more descendant species. Darwin’s Theory of Evolution Evolution or change over time, is the process by which modern organisms have descended from ancient organisms. A scientific Theory is a well-supported testable explanation of phenomena that have occurred in the natural world. Voyage of Beagle Dates: February 12th, 1831 Captain: Charles Darwin Ship: H.M.S. Beagle Destination: Voyage around the world. Findings: evidence to propose a revolutionary hypothesis about how life changes over time Patterns of Diversity Darwin visited Argentina and Australia which had similar grassland ecosystems. Those grasslands were inhabited by very different animals. Neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands Darwin posed challenging questions. Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them? Why were there no kangaroos in England Living Organisms and Fossils Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive today. Others looked completely unlike any creature he had ever seen. As Darwin studied fossils, new questions arose. Why had so many of these species disappeared? How were they related to living species? The Galapagos Island The smallest, lowest islands were hot, dry, and nearly barren-Hood Island-sparse vegetation The higher islands had greater rainfall and a different assortment of plants and animals Isabela-Island had rich vegetation. Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galapagos. Giant tortoises varied in predictable ways from one island to another. The shape of a tortoise’s shell could be used to identify which island a_ particular tortoise inhabited. Animals found in the Galapagos Land Tortoises Darwin Finches Blue-Footed Booby Marine Iguanas The Journey Home Darwin observed that characteristics of many plants and animals vary greatly among the islands Hypothesis:Separate species may have arose from an original ancestor Ideas that shaped Darwin’s Thinking James Hutton: 1795 Theory of Geological change Forces change earth's surface shape Changes are slow Earth much older than thousands of years Charles Lyell Book: Principles of Geography Geographical features can be built up or torn down Darwin thought if earth changed over time, what about life? Lamarck’sTheory of Evolution Tendency toward Perfection (Giraffe necks) Use and Disuse (bird’s using forearms) Inheritance of Acquired Traits Population Growth Thomas = Malthus-19th economist If population grew (more Babies born than die) Insufficient living space Food runs out Darwin applied this theory to animals Publication of Origin of Species Russel Wallace wrote an essay summarizing evolutionary change from his field work in Malaysia Gave Darwin the drive to publish his findings Natural Selection & Artificial Selection Natural variation--differences among individuals of a species Artificial selection-nature provides the variation among different organisms, and humans select those variations they find useful. Evolution by Natural Selection The Struggle for Existence-members of each species have to compete for food, shelter, other life necessities century English 6 Survival of the Fittest-Some individuals better suited for the environment Natural Selection Over time, natural selection results in changes in inherited characteristics of a population. These changes increase a species fitness in its environment Descent Descent with Modification-Each living organism has descended, with changes from other species over time Common Descent-were derived from common ancestors Evidence of Evolution The Fossil Record Geographic Distribution of Living Things Homologous Body Structures Similarities in Early Development The Fossil Record-Layer show change Geographic Distribution of Living Things Homologous Body Structures Similarities in Early Development The Fossil Record Geographic Distribution of Living Things-similar environments have similar types of organisms Homologous Body Structures Similarities in Early Development Homologous Structures Homologous Structures-structures that have different mature forms in different organisms, but develop from the same embryonic tissue Evidence for Evolution Vestigial organs-organs that serve no useful function in an organism i.e.) appendix, miniature legs, arms Summary of Darwin’s Theory Individuals in nature differ from one another Organisms in nature produce more offspring than can survive, and many of those who do not survive do not reproduce Because more organisms are produce than can survive, each species must struggle for resources Each organism is unique, each has advantages and disadvantages in the struggle for existence Individuals best suited for the environment survive and reproduce most successful Species change over time Species alive today descended’ with modification from species that lived in the past All organisms on earth are united into a single family tree of life by common descent Darwin and Human Evolution Lamarck posed the hypothesis about our relation to apes before Darwin Darwin published “Descent of Man” in 1871 caused criticism of his theory, but already the basic ideas of evolution had taken hold in the scientific community What's new in Primates Origins estimated back to 65 MYA Oldest fossil only goes back 45 MYA Insect eating nocturnal mammal Derived traits for life in trees in the tropics Grasping hands and feeteSeparate big toe / thumb Sensitive Skin ridges on hands and feet Large brains -eye hand _ coordination- brachiating Short jaws Forward looking eyes —close together, stereo vision Flat nails —not claws Long parental care with learned behaviors. Single births Fully opposable thumb Primate groups Prosimians include Lemurs, Tarsiers Probably more similar to origin arboreal ancestral primates Anthropoids Include Monkeys, Apes and Humans Split from the Prosimians about 45 M Anthropoids Include the Monkeys and the Hominoids 7 Monkeysevolved in two areas, split about 35 MYA New World monkeys (older), all arboreal have prehensile tail, nostrils open to the sides Squirrel and capuchin monkeys Old World monkeys both arboreal and ground dwellers Lack prehensile tail, nostrils open downwards Rhesus monkey, baboons, macaques Hominoids Include Great Apes and Humans Apes: Gibbons, Orangutan, Chimpanzee/ Bonobo Split from monkeys about 20-25MYA Larger brain size to body size ratios than other primates More flexible behavior (less instinct, more learned behaviors Mostly larger than monkeys (except gibbons) Have long arms, short legs and no tail. Gibbons and orangutans primarily arboreal Gorrillas, Chimps and Humans Social behavior Primarily terrestrial Chimps more closely related to humans than gorilla Hominins (Hominids) All species believed to be more closely related to human than chimpanzees Humans and our direct ancestors, since the split from chimps. Major groups: Australopithecines Paranthropsus Homogenus Chimps are not ancestral species!! We shared a common ancestor. Not a direct line to u!! A radiating lineage. Several hominids species co-existed. Gorillas, chimps and hominids split about 6-8 MYA. At a generous 25year generation time: 320,000 generations ago with strong natural selection Gorillas, the word “organism,” a living thing with organ systems. Cellular organization is seen in something as simple as a fungus cell. From simple bacteria up to mammals, life uses cellular organization. Growth and development Organisms grow and develop following specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young will grow up to exhibit many of the same characteristics as its parents. Although no two look alike, these puppies have inherited genes from both parents and share many of the same characteristics. Living things grow. To conserve resources, organisms reproduce with immature and small copies of themselves. Without straining the parent organism, these small copies gather their own resources to grow, enlarge, mature, age, and reproduce themselves. Humans are excellent examples of growth and development. Eventually, organisms die, returning their gathered resources to the earth for reuse by new organisms. The cycles and stages of life are growth and development. Heredity Life transfers characteristics to offspring via deoxyribonucleic acid (DNA) and ribonucleic acid (RNA); these are the building blocks of life. From viruses to humans, traits that benefit the parents are transferred in genes to the offspring. For humans, this genetic material holds our genetic information such as eye color, skin color, and hair type, just to name a few. Unfortunately, mistakes, mutations, and traits that harm can also be transferred through our genetic material. Whether for good or bad, life exists through heredity. Homeostasis Polar bears (Ursusmaritimus) and other mammals living in ice-covered regions maintain their body temperature by generating 10 heat and reducing heat loss through thick fur and a dense layer of fat under their skin. In order to function properly, cells need to have appropriate conditions such as_ proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental change, through homeostasis (literally, “steady state”)— the ability of an organism to maintain constant internal conditions. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear have body structures that help them withstand low temperatures and conserve body heat. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat. Maintaining a stable internal environment is called homeostasis. Your body, like that of a cat or a cactus, must maintain a stable environment inside. For every inhalation, for example, you need to exhale. If you take food, you must eliminate waste. If you lack enough water for cellular functions, you will get thirsty. Body temperature, a homeostatic biological process, has its mechanical equivalent in the thermostats, regulating room temperature in buildings and homes. Homeostasis is how living organisms maintain their internal system. Metabolism All organisms use a source of energy for their metabolic activities. Some organisms capture energy from the sun and convert it into chemical energy in food (photosynthesis); others use chemical energy in molecules they take in as food (cellular respiration) v The California condor (Gymnogypscalifornianus) uses — chemical energy derived from food to power flight. California condors are an endangered species; this bird has a wing tag that helps biologists identify the individual. Chemical reactions inside cells, tissues, organs, and living beings perform various actions that keep the organism alive. These reactions break down incoming food, send nutrients to cells, remove waste products, transform energy, and synthesize new chemicals. Together, these processes lead to growth, system repair, and excretion. Photosynthesis in plants is a metabolic process. Together, an organism's chemical reactions are its metabolism. Reproduction Single-celled organisms reproduce by first replicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells. Multicellular organisms often produce specialized reproductive germline cells that will form new individuals. When reproduction occurs, genes containing DNA are passed along to an organism's offspring. These genes ensure that the offspring will belong to the same species and will have similar characteristics, such as size and shape. Successful organisms reproduce Response to Stimuli Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch. The leaves of this sensitive plant (Mimosapudica) will instantly droop and fold when touched. After a few minutes, the plant returns to normal. Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response. Scientists 11 have been able to coax crystal structures to change behavior when exposed to blue light. Though this does not mean the crystals are alive, they exhibit a response to a stimulus, just as you respond to having your name called or your leg pinched. Phototropism is a plant's response to stimuli (turning toward the light). Everything alive shows a response to stimuli. What are the characteristics of a cell? The basic organizing structure of living things is the cell, a small version of the larger organism's processes. Individual cells carry on life process themselves. The Characteristics of a cell: 1.Cells separate themselves from __ their environment with cell walls, called cell membranes 2.Cells carry on homeostasis with cytoplasm, the liquid inside the membrane and the medium holding the organelles, or cell structures 3.Organelles carry on metabolism and other life processes within the cell membrane 4.All cells carry their own heredity markers, DNA, at some stage of their development (though some, like red blood cells in humans, do not have DNA at maturity) 5.Cells differentiate and build on these basic functions by either not having a nucleus (prokaryotic) or having a nucleus (eukaryotic). Are Bacteria living or nonliving? 1.Adaptation through evolution—Bacteria evolve; they evolve quickly because they can reproduce at an incredibly fast rate. 2.Cellular organization—Bacteria, by definition are single cells, but they are cells with cell walls, ribosomes, flagella, and DNA 3.Growth and development—Bacteria do not show growth and development the same way higher forms of life do, but one bacterium splits into two daughter cells as part of a life cycle of lag phase, logarithm phase, stationary phase, and death phase 4.Heredity—-Bacteria contain DNA and, typically, RNA 5.Homeostasis—Bacteria use their cell membranes to perform homeostasis 6. Metabolism -Autotrophs (unique to bacteria), photosynthesis, anaerobic respiration, heterotrophic metabolism, fermentation, and the Krebs cycle are all aspects of bacterial metabolism. 7.Reproduction-Through binary cell division, bacteria reproduce in exponential numbers in very short periods compared to higher forms of life 8.Response to stimuli-Chemotaxis describes bacteria moving toward or away from chemicals, such as Escherichia coli moving toward glucose 9.Bacteria meet all the requirements for being considered living things. Bacteria are alive. Are viruses living organisms? Viruses are trickier to classify than bacteria. Let's use our trusty list again: 1.Adaptation through evolution—Viruses can mutate and evolve; this is one aspect of their behavior that makes them so difficult to fight when they infect populations 2.Cellular organization—-Viruses have no cells 3.Growth and development-Viruses Show Evidence of growth and development 4.Heredity —Viruses contain either DNA or RNA; seldom do they possess both 5.Homeostasis -Viruses cannot perform homeostasis 6.Metabolism -Viruses do not have metabolism 7.Reproduction —Viruses can only reproduce inside the cells of other organisms, which they do at astoundingly high rates 8.Response to stimuli —Viruses do not respond to stimuli Levels of Organization of Living Things Living things are highly organized and structured, following a hierarchy that can be examined on a scale from small to large. 12 The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules. A molecule is a chemical structure consisting of at least two atoms held together by one or more chemical bonds. Many molecules that are biologically important are macromolecules, large molecules that are typically formed by polymerization (a polymer is a large molecule that is made by combining smaller units called monomers, which are simpler — than macromolecules). An example of a macromolecule is deoxyribonucleic acid (DNA), which contains the instructions for the structure and functioning of all living organisms. All molecules, including this DNA molecule, are composed of atoms. Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells. Examples of organelles include mitochondria and chloroplasts, which carry out indispensable functions: mitochondria produce energy to power the cell, while chloroplasts enable green plants to utilize the energy in sunlight to make sugars. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack the reproductive mechanism of a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes Are single-celled or colonial organisms that do not have membrane-bound nuclei or organelles; in contrast, the cells of eukaryotes have membrane-bound organelles and a membrane-bound nucleus. common in human daily life, encountered many more times than the archae bacteria. Eubacteria can be found almost everywhere and kill thousands upon thousands of people each year, but also serve as _ antibiotics producers and food digesters in our stomachs. The Bacteria’ possess the following characteristics: a. Bacteria are prokaryotic cells. b. Like the Eukarya, they have membranes composed of unbranched fatty acid chains attached to glycerol by ester linkages. c. The cell walls of Bacteria, unlike the Archaea and the Eukarya, contain peptidoglycan. d. Bacteria are sensitive to traditional antibacterial antibiotics but are resistant to most antibiotics that affect Eukarya. e. Bacteria contain rRNA that is unique to the Bacteria as indicated by the presence of molecular regions distinctly different from the tRNA of Archaea and Eukarya. Bacteria include mycoplasmas, cyanobacteria, Gram-positive bacteria, and Gram-negative bacteria. The Eukarya (eukaryotes) The Eukarya (also spelled Eucarya) possess the following characteristics: a. Eukarya have eukaryotic cells. b. Like the Bacteria, they have membranes composed of unbranched fatty acid chains attached to glycerol by ester linkages. c. Not all Eukarya possess cells with a cell wall, but for those Eukarya having a cell wall, that wall contains no peptidoglycan. d. Eukarya are resistant to traditional antibacterial antibiotics but are sensitive to most antibiotics that affect eukaryotic cells. e. Eukarya contain rRNA that is unique to the Eukarya as indicated by the presence of molecular regions distinctly different from the tRNA of Archaea and Bacteria. The Eukarya are subdivided into the following four kingdoms: 15 1. Protista Kingdom: Protists are simple, predominantly unicellular eukaryotic organisms. Examples include slime molds, euglena, algae, and protozoans. 2. Fungi Kingdom: Fungi are unicellular or multicellular organisms with eukaryotic cell types. The cells have cell walls but are not organized into tissues. They do not carry out photosynthesis and obtain nutrients through absorption. Examples include sac fungi, club fungi, yeasts, and molds. 3. Plantae Kingdom: Plants are multicellular organisms composed of eukaryotic cells. The cells are organized into tissues and have cell walls. They obtain nutrients by photosynthesis and absorption. Examples include mosses, ferns, conifers, and flowering plants. 4. Animalia Kingdom: Animals are multicellular organisms composed of eukaryotic cells. The cells are organized into tissues and lack cell walls. They do not carry out photosynthesis and obtain nutrients primarily by ingestion. Examples include sponges, worms, insects, and vertebrates. It used to be thought that the changes that allow microorganisms to adapt to new environments or alter their virulence capabilities was a relatively slow process occurring within an organism primarily through mutations, chromosomal rearrangements, gene deletions and gene duplications. Those changes would then be passed on to that microbe's progeny and natural selection would occur. This gene transfer from a_ parent organism to its offspring is called vertical gene transmission. It is now Known that microbial genes are transferred not only vertically from a parent organism to its progeny, but also horizontally to relatives that are only distantly related, e.g., other species and other genera. This latter process is Known as horizontal gene transfer. Through mechanisms such as transformation, transduction, and conjugation, genetic elements such as plasmids, transposons, integrons, and even chromosomal DNA can readily be spread from one microorganism to another. As a result, the old three-branched “tree of life" in regard to microorganisms. now appears to be more of a “net of life. “Microbes are known to live in remarkably diverse environments, many of which are extremely harsh. This amazing and rapid adaptability is a result of their ability to quickly modify their repertoire of protein functions by modifying, gaining, or losing their genes. This gene expansion predominantly takes place by horizontal transfer. Summary 1. Phylogeny refers to the evolutionary relationships between organisms. 2. Organisms can be classified into one of three domains based on differences in the sequences of nucleotides in the cell's ribosomal RNAs (rRNA), the cell’s membrane lipid structure, and its sensitivity to antibiotics. 3. The three domains are the Archaea, the Bacteria, and the Eukarya. 4. Prokaryotic organisms belong either to the domain Archaea or the domain Bacteria; organisms with eukaryotic cells belong to the domain Eukarya. 5. Microorganisms transfer genes to other microorganisms through horizontal gene transfer -the transfer of DNA to an organism that is not its offspring. During Linnaeus’s time, living things were classified as either animals or as_ plants. Animals were organisms that moved from place to place and used food for energy. Plants were green organisms that generally did not move and got their energy from the sun. As biologists learned more about the natural world, they realized that Linnaeus’s two kingdoms—Animalia and Plantae—did not reflect the full diversity of life. Classification systems have changed dramatically since Linnaeus's time, and 16 hypotheses about relationships among organisms are still changing today as new data are gathered. FIVE KINGDOMS At first, all microorganisms were placed in their own kingdom, named Protista. Later, yeasts and molds, along with mushrooms, were placed in their own kingdom, Fungi. Later still, scientists realized that bacteria lack the nuclei, mitochondria, and chloroplasts found in other forms of life. All prokaryotes (bacteria) were placed in yet another new kingdom, Monera. Single-celled eukaryotic organisms remained in the kingdom Protista SIX KINGDOMS By the 1990s, researchers had learned that the organisms in kingdom Monera were actually two genetically and biochemically different groups. THREE DOMAINS Genetic analysis has revealed that the two main prokaryotic kingdoms are more different from each other, and from eukaryotes, than previously thought. So, biologists established a new taxonomic category—the domain. A domain is a larger, more inclusive category than a kingdom. Under this system, there are three domains— domain Bacteria (corresponding to domain Eubacteria), domain Archaea (corresponding to kingdom Archaebacteria), and domain Eukarya (corresponding to kingdoms Fungi, Plantae, Animalia, and kingdom “Protista”). Quotes are put around kingdom “Protista” to indicate that it is not a monophyletic group. THE TREE OF LIFE The tree of life shows current hypotheses regarding evolutionary relationships among the taxa within the three domains of life. Modern evolutionary classification is a rapidly changing science with the difficult goal of presenting all life on a single evolutionary tree. The tree of life shows current hypotheses regarding evolutionary relationships among the taxa within the three domains. DOMAIN BACTERIA Members of the domain Bacteria are unicellular and prokaryotic. This domain corresponds to the kingdom Eubacteria. Their cells have thick, rigid walls that surround a cell membrane and contain a substance known as peptidoglycan. These bacteria are ecologically diverse, ranging from free-living soil organisms to deadly parasites. Some photosynthesize, while others do not. Some need oxygen to survive, while others are killed by oxygen. DOMAIN ARCHAEA The domain Archaea corresponds to the kingdom Archaebacteria. Members of the domain Archaea are unicellular and prokaryotic, and they live in some extreme environments—in volcanic hot springs, brine pools, and black organic mud totally devoid of oxygen. Many of these bacteria can survive only in the absence of oxygen. Their cell walls lack peptidoglycan, and their cell membranes contain unusual lipids that are not found in any other organism. DOMAIN EUKARYA The domain Eukarya consists of all organisms that have a nucleus. It comprises the four remaining kingdoms of the six-kingdom system: “Protista,” Fungi, Plantae, and Animalia. 17 THE “PROTISTS”: UNICELLULAR EUKARYOTES The kingdom Protista has long been viewed by biologists as a “catchall” group of eukaryotes that could not be classified as fungi, plants, or animals. Recent molecular studies and _ cladistic analyses have shown that “the eukaryotes formerly known as “Protista” do not form a single clade. Current cladistic analysis divides these organisms into at least five clades. Since these organisms cannot be _ properly placed into a single taxon, we refer to them as “protists.” Most “protists” are unicellular, but one group, the brown algae, is multicellular. Some ‘“protists" are photosynthetic, while others are heterotrophic. Some display characters that resemble those of fungi, plants, or animals. FUNGI Members of the kingdom Fungi are heterotrophs with cell walls containing chitin. Most fungi feed on dead or decaying organic matter. They secrete digestive enzymes into their food source, which break the food down into smaller molecules. The fungi then absorb these smaller molecules into their bodies. Mushrooms and other recognizable fungi are multicellular, like the ghost fungus shown. Some __fungi--yeasts, for example—are unicellular. PLANTAE Members of the kingdom Plantae are multicellular, have cell walls that contain cellulose, and are autotrophic. Autotrophic plants are able to carry on photosynthesis using chlorophyll. Plants are nonmotile—they cannot move from place to place. The entire plant kingdom is the sister group to the red algae, which are “protists.” considered the standard phylogeny for many years. The Role of Genetics in Modern Taxonomy Haeckel's and Whittaker’s trees presented hypotheses about the phylogeny of different organisms based on readily observable characteristics. But the advent of molecular genetics in the late 20th century revealed other ways to organize phylogenetic trees. Genetic methods allow for a standardized way to compare all living organisms without relying on observable characteristics that can often be subjective. Modern taxonomy relies heavily on comparing the nucleic acids (deoxyribonucleic acid [DNA] or ribonucleic acid [RNA]) or proteins from different organisms. The more similar the nucleic acids and proteins are between two organisms, the more closely related they are considered to be. In the 1970s, American microbiologist Carl Woese discovered what appeared to be a “living record” of the evolution of organisms. He and his collaborator George Fox created a genetics-based tree of life based on similarities and differences they observed in the small subunit ribosomal RNA (rRNA) of different organisms. In the process, they discovered that a certain type of _ bacteria, called archaebacteria(now known simply as archaea), were significantly different from other bacteria and eukaryotes in terms of the sequence of small subunit rRNA. To accommodate this difference, they created a tree with three Domains above the level of the Kingdom: Archaea, Bacteria, and Eukarya. Genetic analysis of the small subunit rRNA suggests archaea, bacteria, and eukaryotes all evolved from a common ancestral cell type. The tree is skewed to show a closer evolutionary relationship between Archaea and Eukarya than they have to Bacteria. Scientists continue to use analysis of RNA, DNA, and proteins to determine how organisms are related. One interesting, and 20 complicated, discovery is that of horizontal gene transfer—when a gene of one species is absorbed into another organism’s genome. Horizontal gene transfer is especially common in microorganisms and can make it difficult to determine how organisms are evolutionarily related. Consequently, some scientists now think in terms of “webs of life” rather than “trees of life.” Classification and Phylogeny Scientists use a tool called a phylogenetic tree to show the evolutionary pathways and relationships between organisms. A phylogenetic tree is a diagram used to reflect evolutionary relationships among organisms or groups of organisms. The _ hierarchical classification of groups nested within more inclusive groups is reflected in diagram Scientists consider phylogenetic trees to be a hypothesis of the evolutionary past because one cannot go back through time to confirm the proposed relationships. Unlike with a taxonomic classification, a phylogenetic tree can be read like a map of evolutionary history. Shared characteristics are used to construct phylogenetic trees. The point where a split occurs in a tree, called a branch point, represents where a single lineage evolved into distinct new ones. Many phylogenetic trees have a single branch point at the base representing a common ancestor of all the branches in the tree. Scientists call such trees rooted, which means there is a single ancestral taxon at the base of a phylogenetic tree to which all organisms represented in the diagram descend from. When two lineages stem from the same branch point, they are called sister taxa, for example the two species of orangutans. A branch point with more than two groups illustrates a situation for which scientists have not definitively determined relationships. An example is illustrated by the three branches leading to the gorilla subspecies; their exact relationships are not yet understood. It is important to note that sister taxa share an ancestor, which does not mean that one taxon evolved from the other. The branch point, or split, represents a common ancestor that existed in the past, but that no longer exists. Humans did not evolve from chimpanzees (nor did chimpanzees evolve from humans) although they are our closest living relatives. Both humans and chimpanzees evolved from a common ancestor that lived, scientists believe, six million years ago and looked different from both modern chimpanzees and modern humans. both modern chimpanzees and modern humans. A phylogenetic tree is rooted and shows how different organisms, in this case the species and subspecies of living apes, evolved from a common ancestor. Another aspect of phylogenetic trees is that, unless otherwise indicated, the branches do not show length of time, they show only the order in time of evolutionary events. In other words, a long branch does not necessarily mean more time passed, nor does a short branch mean less time passed—unless specified on the diagram. Carolus linnaeus - he’s most famous for is creating the system called binomial nomenclature this is the system of given every organism two names. BINOMIAL NOMENCLATURE- giving organisms two names GENUS+SPECIES Taxonomy: The science of classification. Taxonomy means giving names to things. Taxon- individual levels used to classify organisms Classification is a very broad term which simply means putting things into groups. system of 21 A species is... A group of organisms with _ similar characteristics. Produce fertile offspring. Similar DNA. Phylogeny -The history of a species as they change through time. Who came from whom? Dichotomous key: A tool that allows the user to determine the identity of items in the natural world. Based on characteristics and uses process of comparison and elimination. Classification uses... Homology — Similarities between organisms Adapted traits may further subdivide species into subspecies. Canis lupus articus. The 3 domains of life. All life is either... Archaeabacteria Eubacteria Eukarya The Kingdoms of life. All life belongs to one of these. The 8 Taxonomic ranks. have 8 names. 1) Domain - Did 2) Kingdom - King 3) Phylum - Phillip 4) Class - Come 5) Order - Over 6) Family - For 7) Genus - Good 8) Species - Spaghetti All living things Genus name is Capitalized; species name is not. They are both italicized. Ex) Armadiillidium vulgare DOMAIN = KINGDOM — PHYLUM = CLASS += ORDER -— FAMILY = GENUS -— SPECIES Humans Taxonomic Classification -Domain - Eukarya -Kingdom - Animalia -Phylum - Chordata -Class - Mammalia -Order - Primatdae -Family - Hominidae -Genus - Homo -Species - Sapien Area of focus: Bacteria Eubacteria) (Kingdom Prokaryotic (No nucleus) and no_ internal organelles. Has a cell wall. DNA floats in cell Two types: 1.) Archaea — old 2.) Eubacteria —true Eubacteria — True bacteria, gets energy from food or sun. Sphere (Round) Shaped — Cocci Rod shaped — Bacilli Spiral shaped — Spirilla Mycoplasma bacteria — smallest known life form (jagged and random). Diplo = Pair Tetrad = Groups of four Sarcinae = Groups of Eight. Staphylo = Cluster Strepto = Chain Blue-Green Algae: Also called Cyanobacteria. It is photosynthetic (gets energy from sun). Gram staining: Technique used to identify bacteria. Pink and Red: Gram Negative 22 Gram Positive = Dark Purple Bacterial food borne illness can be prevented by.... controlling the initial number of bacteria present. Refrigeration Prevents the small number of bacteria from growing rapidly. Destroying the bacteria by proper cooking. Avoiding re-contamination. Clean cutting board immediately after use. Penicillin: Antibiotic that destroys bacteria derived from penicillin mold (fungi). Antiseptic - agent that kills or inhibits the growth of microorganisms on the external surfaces of the body. Plaque is the accumulation of bacteria and micro-organisms on a tooth. Tartar is dental plaque that has mineralized. Tartar can form when plaque is not removed from the tooth surfaces. Binary Fission: The process by which a bacterium multiplies by splitting in two. In asexual reproduction, one __ individual produces offspring that are genetically identical to itself. Sexual Reproduction: Genetic material from two different individuals combines into a genetically unique offspring. Positives (+) Food Source Recycling waste Industrial Decomposition Negatives (-) Health Problems Destroys Food New Area of Focus: Eukarya vvve?°? Mycophycophyta / Lichens: Fungi and algae live together (symbiotic) Deuteromycota / Imperfect Fungi: The leftovers ©. Includes Athletes foot. Basidiomycota / Club Fungi: Mushrooms. Decomposition of wood. The 3 Roles of Fungi Mutualistic symbionts — organisms (plants) grow. Hyphae / Part of the Mycelium- The part of the fungus that feeds, grows, and ultimately may produce a mushroom. Saprobic- decomposes dead _things...logs, feces, corpses, and recycles nutrients. Parasitic- Fungi absorbs nutrients (SPONCH) from living cells. A few final thoughts on Fungi. Mold prevention. Fermentation. Asexually, Fungi reproduce by: Budding / Splitting in two. Fragmentation / Break off and grow. Sporulation / releases spores which are tiny repoductive bodies. Some fungi reproduce sexually, where two haploid spores form a diploid. Spores are microscopic and travel through the air. Storage containers help but spores will always enter. To prevent mold growth limit. New Area of Focus: Kingdom Plantae. Fungus helps Plants: Have cells walls and make their own food (photosynthesis), and lack the power of locomotion. Plants are divided into Divisions instead of Phylum. 25 Classification & Introduction to Taxonomy Classification ¢ The grouping of objects or information based on similarities. ¢ There are more than 1 million described species of plants and animals—Many millions still left undescribed Taxonomy * Science of classification (grouping things)—Process of classifying biodiversity based on_ evolutionary relationships ¢ Means to organize biological diversity ¢ Groups and names organisms based on different characteristics Early Taxonomic Systems ¢ Aristotle (8350 B.C.)—Developed the 1st widely accepted system of biological classification ¢ Everything grouped as plant or animal PLANT = herbs, shrubs, trees ANIMALS = land, sea, air Early Taxonomic Systems ¢ Carolus Linnaeus (1753)-use of a species name « Based on looking at physical and structural similarities « Revealed relationships of organisms ¢ Binomial nomenclature o Gave each species 2 names (scientific name) o Genus and species o Genus is a group of similar species ¢ Developed the modern system of taxonomy ¢ Latin was the language used (no longer used and is not being changed) ¢ Genus name=always capitalized * species name=always lowercase ¢ both names MUST be underlined or italicized ¢ Ex: Canislupus(wolf) ¢ Ex:Homosapiens(human) Scientific names are often: ¢ Descriptive (AcerrubrumUred maple) « Named after someone (genusOLinnea)— Descriptive of where an organism lives (D.californica) ¢ Named after person who first described the organism (D.californicaTorr) « Many organisms have common names * Can be misleading ¢ Can have more than 1 common name, depending on the area it is found in Modern Taxonomy ¢« Now based on evolutionary relationships ¢ Taxonomists study: 0 Structural similarities o Chromosomal (karyotypes) o Reproductive potential 0 Biochemical similarities = Comparing DNA _— and amino acids o Embryology/development o Breeding behavior 0 Geographic distribution structure 7 taxonomic categories: Kingdom = largest, most general group Phylum = called a division with plants Class 26 Order Family Genus Species = smallest, most specific group ¢ Grouped genera into families, families into orders, orders into classes, classes into phyla, and phyla into kingdoms * Species can interbreed with each other 1969: 5-Kingdom System ¢ Monera, Protista, and Fungi kingdoms added to the 2 established kingdoms ¢ Kingdoms defined based on 2 main characteristics ¢ Possession of a_ true (prokaryote or eukaryote) ¢ Howit gets food o Heterotroph o Autotroph o Decomposer nucleus 1980’s: 3-Domain System ¢ Bacteria have distinct differences ¢ All eukaryotic kingdoms grouped into one domain (Eukarya) ¢ Monera kingdom split into 2 domains (Archaea and Eubacteria) How Living Things Are Classified ¢ Groups of organisms called taxa or taxons. ¢ Organisms arranged in groups ranging from very broad to very specific characteristics o Broader taxons have more general characteristics and more species within it ¢ Smallest taxon = Species ¢ Largest taxon = Kingdom Phylogeny ¢ a family tree for the history of a species o The root of the tree represents the ancestral lineage o Tips of the branches represent descendants of the ancestor o Movement upward shows forward motion through time oO Speciation: split in the lineage o Shown as a branching of the tree evolutionary Cladistics « System of classification based on phylogeny o Derived characteristics/traits: appear in recent parts of a lineage but not in older members Cladogram ¢ A branching diagram to show the evolutionary history of a species ¢ Helps scientists understand how one lineage branched from another in the course of evolution Dichotomous Key ¢ Way of identifying organisms by looking at the physical characteristics « Uses a series of questions to group into a hierarchy classification The Six Kingdoms of Organisms Prokaryotes: o Microscopic 0 Prokaryotic (Lack a nucleus) o Can be autotrophs (photosynthetic or chemosynthetic) or heterotrophs 0 Unicellular 27 ¢ 2 kingdoms (Archaebacteria and Eubacteria) ¢ Archaebacteria live in extreme environments like swamps, deep-ocean hydrothermal vents (oxygen-free environments) o Cell walls not made of peptidoglycan o Ex: Methanogens, Halophiles ¢ Eubacteria live in most habitats o Cell walls made of peptidoglycan o Ex: EE. coli, Streptococcus, cyanobacteria Protista ¢ Eukaryotic (has a nucleus) * Some have cell walls of cellulose o Some have chloroplasts * Can be autotrophs or heterotrophs (some can be fungus-like) * Most are unicellular; some are multicellular or colonial o EX: amoeba, paramecium, slime molds, euglena, kelp « Lacks complex organ systems ¢ Lives in moist environments ¢ Eukaryotes * Cell walls of chitin ¢ Heterotrophs ¢ Most multicellular; some unicellular o EX: mushrooms, yeast ¢ Absorbs nutrients from organic materials in the environment ¢ Stationary Plants ¢ Eukaryotes * Cell walls of cellulose ¢ Autotrophs ¢ = Multicellular ¢ Photosynthetic = contains chloroplasts The plasma membrane functions as a selective barrier that allows the passage of oxygen, nutrients, and wastes for the whole volume of the cell. Larger organisms do not generally have larger cells than smaller organisms— simply more cells Internal membranes compartmentalize the functions of a eukaryotic cell. A eukaryotic cell has extensive and elaborate internal membranes, which partition the cell into compartments. The compartments created by membranes provide different local environments that facilitate specific metabolic functions, allowing several incompatible processes to go on simultaneously in a cell. The general structure of a biological membrane is a double layer of phospholipids. Other lipids and diverse proteins are embedded in the lipid bilayer or attached to its surface Each type of membrane has a unique combination of lipids and proteins for its specific functions. Concept: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the genes in a eukaryotic cell.oAdditional genes are —_ located in mitochondriaand chloroplasts. The nucleus is separated from the cytoplasm by a double membrane called the nuclear envelope. o The two membranes of the nuclear envelopeare separated by 20-40 nm. 30 o The envelope is perforated by pores that areabout 100 nm in diameter. oO At the lip of each pore, the inner and outer membranes of the nuclear envelope are fused to form a continuous membrane. o A protein structure called a pore complex lines each pore, regulating the passage of certain large macromolecules and particles. The nuclear side of the envelope is lined by the nuclear lamina, a network of protein filaments that maintains the shape of the nucleus There is evidence that a framework of fibers called the nuclear matrix extends through the nuclear interior. Within the nucleus, the DNA and associated proteins are organized into discrete units called chromosomes, structures that carry the genetic information. Each chromosome is made up of fibrous material called chromatin, a complex of proteins and DNA. As the cell prepares to divide, the chromatin fibers coil up and condense, becoming thick enough to be recognized as the familiar chromosomes. Each eukaryotic species has a characteristic number of chromosomes o A typical human cell has 46 chromosomes. o A human sex cell (egg or sperm) has only 23 chromosomes. In the nucleus is a region of densely stained fibers and granules adjoining chromatin, the nucleolus. o In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits o The subunits pass through the nuclear poresto the cytoplasm, where they combine to form ribosomes. The nucleus directs protein synthesis by synthesizing messenger RNA (MRNA). o The mRNA travels to the cytoplasm through the nuclear pores and combines’ with ribosomes to translate its genetic message into the primary structure of a specific polypeptide Ribosomes build a cell’s proteins. Ribosomes, containing rRNA and protein, are the organelles that carry out protein synthesis. o Cell types that synthesize large quantities of proteins (e.g., pancreas cells) have large numbers of ribosomes and prominent nucleoli. Some ribosomes, free ribosomes, are suspended in the cytosol and synthesize proteins that function within the cytosol. Other ribosomes, bound ribosomes, are attached to the outside of the endoplasmic reticulum or nuclear envelope. o These synthesize proteins that are either included in membranes or exported from the cell o Ribosomes can_ shift between roles depending on the polypeptides they are synthesizing. The endoplasmic 31 These membranes are either directly continuousor connected via transfer of vesicles, sacs of membrane. The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane. reticulum manufactures membranes and performs many other biosynthetic functions. The endoplasmic reticulum (ER) accounts for half the membranes in a eukaryotic cell. The ER includes membranous tubules and internal, fluid-filled spaces called cisternae. The ER membrane is continuous with the nuclear envelope, and the cisternal space of the ER is continuous with the space between the two membranes of the nuclear envelope There are two connected regions of ER that differ in structure and function. Smooth ER looks smooth because it lacks ribosomes. o Rough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope. The smooth ER is rich in enzymes and playsa role in a variety of metabolic processes. o Enzymes of smooth ER synthesize lipids, including oils, phospholipids, and steroids. oO These include the sex hormones of vertebrates and adrenal Concept: The endomembrane = system regulates protein traffic and performs steroids. metabolic functions in the cell o In the smooth ER of the liver, ¢ Many of the internal membranes in a enzymes help detoxify poisons eukaryotic cell are part of the and drugs such asalcohol and endomembrane system. barbiturates. = Frequent use of these drugs leads to the proliferation of smooth ER in liver cells, increasing the rate of detoxification. = This increases tolerance to the target and other drugs, so higher doses are required to achieve the same effect. Smooth ER stores calcium ions. o Muscle cells have a specialized smooth ER that pumps calcium ionsfrom the cytosol and stores them in its cisternal space. oO When a nerve impulse stimulates a muscle cell, calcium ions rush from the ER into the cytosol, triggering contraction. o Enzymes then pump the calcium back, readying the cell for the next stimulation Rough ER is especially abundant in cells that secrete proteins. Rough ER is also a membrane factory. oO Membrane-bound proteins are synthesized directly into the membrane. o Enzymes in the rough ER also synthesize phospholipids from precursors in the cytosol. o As the ER membrane expands, membrane can be transferred as transport vesicles to other components of the endomembrane system. The Golgi apparatus is the shipping and receiving center for cell products. Many transport vesicles from the ER travel to the Golgi apparatus for modification of their contents. 32 The Golgi is a_ center’ of manufacturing, warehousing, sorting, and shipping. The Golgi apparatus is especially extensive in cells specialized for secretion. o The Golgi apparatus consists of flattened membranous — sacs called cisternae.oThe membrane of each cisterna separates its internal space from the cytosol. o One side of the Golgi, the cis side, is locatednear the ER. The cis face receives material by fusing with transport vesicles from the ER. o The other side, the trans side, buds off vesicles that travel to other sites. During their transit from the cis to the trans side, products from the ER are usually modified. The Golgi can also manufacture its own macromolecules, including pectin and other non-cellulose polysaccharides. The Golgi apparatus is a very dynamic structure. Finally, the Golgi sorts and packages materials into transport vesicles Lysosomes are digestive compartments. A lysosome is a membrane-bound sac of hydrolytic enzymes that an animal cell uses to digest macromolecules. Lysosomal enzymes can_ hydrolyze proteins, fats, polysaccharides, and nucleic acids. These enzymes work best at pH 5. o Rupture of one or a_ few lysosomes has little impact on a cell because the lysosomal enzymes are not very active at the neutral pH of the cytosol. o The membranes of the chloroplast divide thechloroplast into three compartments: the intermembrane space, the stroma, and the thylakoid space. Like mitochondria, chloroplasts are dynamic structures. o They can reproduce themselves by pinchingin two. Mitochondria and _ chloroplasts are mobile and move around the cell along tracks of the cytoskeleton. Peroxisomes generate and degrade H202 in performing various metabolic functions. Peroxisomes contain transfer hydrogen substrates to oxygen. o An intermediate product of this process is hydrogen peroxide (H202), a poison. o The peroxisome contains an enzyme that converts H202 to water. o Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria as fuel for cellular respiration. oO Peroxisomes in the liver detoxify alcohol andother harmful compounds. oO Specialized peroxisomes, glyoxysomes, convert the fatty acids in seeds to sugars, which the seedling can use as a source of energy and carbon until it is capable of photosynthesis. Peroxisomes are bound by a single membrane. They form not from the endomembrane system, but by incorporation of proteins and lipids from the cytosol. They split in two when they reach a certain size. enzymes that from various 35 Concept: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers extending throughout the cytoplasm. The cytoskeleton organizes the structures and activities of the cell.The cytoskeleton provides support, motility, and regulation. The cytoskeleton provides mechanical support and maintains cell shape. The cytoskeleton provides anchorage for many organelles and_ cytosolic enzymes. The cytoskeleton is dynamic and can be dismantled in one part and reassembled in another to change the shape of the cell. The cytoskeleton also plays a major role in cell motility, including changes in cell location and limited movements of parts of the cell. Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton The cytoskeleton manipulates the plasma membrane to form food vacuoles during phagocytosis. Cytoplasmic streaming in plant cells is caused by the cytoskeleton. Recently, evidence suggests that the cytoskeleton may play a role in the regulation of biochemical activities in the cell. There are three main types of fibers making up the cytoskeleton: microtubules, microfilaments, and intermediate filaments. Microtubules, the thickest fibers, are hollow rodsabout 25 microns in diameter and 200 nm to 25 microns in length. 0 Microtubule fibers are constructed of the globular protein tubulin. o Each tubulin molecule is a dimer consisting of two subunits. o A microtubule changes in length by adding or removing tubulin dimers. Microtubules shape and support the cell and serve as tracks to guide motor proteins carrying organelles to their destination. Microtubules are also responsible for the separation of chromosomes during cell division. In many cells, microtubules grow out from a centrosome near the nucleus In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubulesarranged in a ring. o Before a_ cell divides, the centrioles replicate. A specialized arrangement of microtubules is responsible for the beating of cilia and flagella. o Many — unicellular eukaryotic organisms are propelled through water by cilia and flagella. o Cilia or flagella can extend from cells within a tissue layer, beating to move fluid over thesurface of the tissue. Cilia usually occur in large numbers on the cell surface. There are usually just one or a few flagella per cell. Cilia and flagella differ in their beating patterns. In spite of their differences, both cilia and flagella have the same ultrastructure. o Both have a core of microtubules sheathed by the plasma membrane. o Nine doublets of microtubules are arranged in a ring around a pair at the center. This “9 + 2” pattern 36 is found in nearly all eukaryotic cilia and flagella. Microfilaments are solid rods about 7 nm in diameter The structural role of microfilaments in the cytoskeleton is to bear tension, resisting pulling forces within the cell. They form a three-dimensional network just inside the plasma membrane to help support thecell’s shape, giving the cell cortex the semisolid consistency of a gel. Microfilaments are important in cell motility, especially as part of the contractile apparatus of muscle cells. Intermediate filaments range in diameter from 8-12 nanometers, larger than microfilaments but smaller — than microtubules. o Intermediate filaments are a diverse class of cytoskeletal units, built from a family of proteins called keratins.ointermediate _ filaments are specialized for bearing tension. Intermediate filaments are more permanent fixtures of the cytoskeleton than are the other two classes. They reinforce cell shape and fix organelle location Concept: Extracellular components and connections between cells help coordinate cellular activities Plant cells are encased by cell walls. The cell wall, found in prokaryotes, fungi, and some protists, has multiple functions. In plants, the cell wall protects the cell, maintains its shape, and _ prevents excessive uptake of water. It also supports the plant against the force of gravity. The thickness and chemical composition of cell walls differs from species to species and among cell types within a plant. A mature cell wall consists of a primary cell wall,a middle lamella with sticky polysaccharides thatholds cells together, and layers of secondary cellwall. Plant cell walls are perforated by channels between adjacent cells called plasmodesmata The extracellular matrix (ECM) of animal cells functions in support, adhesion, movement, and regulation. ¢ Though lacking cell walls, animal cells do have’ an_ elaborate extracellular matrix (ECM). « The primary constituents of the extracellular matrix are glycoproteins, especially collagen fibers, embedded in a network of glycoprotein proteoglycans. « The ECM can_ regulate cell behavior.Intercellular junctions help integrate cells into higher levels of structure and function. ¢ Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact. « Plant cells are perforated with plasmodesmata, channels allowing cytosol to pass between cells. o Water and small solutes can pass freely from cell to cell. o In certain circumstances, proteins and RNA can be exchanged. « Animals have 3 main types of intercellular links: tight junctions, desmosomes, and gap junctions. 37 ¢ In tight junctions, membranes of adjacent cells are fused, forming continuous belts around cells. o This prevents leakage of extracellular fluid. « Desmosomes (or anchoring junctions) fasten cells together into strong sheets, much like rivets ¢ Gap junctions (or communicating junctions) provide cytoplasmic channels between adjacent cells. A cell is a living unit greater than the sum of its parts. « While the cell has many structures with specific functions, all these structures must work together. « The enzymes of the lysosomes and proteins of the cytoskeleton are synthesized on the ribosomes. ¢ The information for the proteins comes from genetic messages sent by DNA in the nucleus. ¢ All of these processes require energy in the formof ATP, most of which is supplied by the mitochondria. ¢ Acellis a living unit greater than the sum of its parts. Cell Cycle and Cell Division The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughtercells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages ofgrowth, DNA replication, and division that produces two_ identical (clone) cells. The cell cycle has two major phases: interphase and _ the mitotic phase. During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA _ and