Biology book1

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Biology book1

  1. 1. Table of ContentsBiology: The Science of Our Lives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Science and the Scientific Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Theories Contributing to Modern Biology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Development of the Theory of Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5The Modern View of the Age of the Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Development of the Modern View of Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Darwinian Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7The Diversity of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Characteristics of Living things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Levels of Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Structure of Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Organic Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Origin of the Earth and Life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Is There Life on Mars, Venus, Anywhere Else?? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29Terms Applied to Cells. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Components of Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31The Origins of Multicellularity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Microscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Cell Size and Shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35The Cell Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36The Nucleus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Ribosomes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Endoplasmic Reticulum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Golgi Apparatus and Dictyosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Mitochondria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Cell Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Water and Solute Movement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Cells and Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Active and Passive Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Carrier-assisted Transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Types of transport molecules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Vesicle-mediated transport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48The Cell Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Prokaryotic Cell Division. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Eukaryotic Cell Division. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Mitosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Life Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Phases of Meiosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Comparison of Mitosis and Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Laws of Thermodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Potential vs. Kinetic energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 1
  2. 2. Table of Contents ContinuedEndergonic and exergonic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Oxidation/Reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Enzymes: Organic Catalysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61The Nature of ATP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Glycolysis, the Universal Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Anaerobic Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Aerobic Respiration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67What is Photosynthesis? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Leaves and Leaf Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69The Nature of Light. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Chlorophyll and Accessory Pigments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70Stages of Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72C-4 Pathway. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74The Carbon Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Review Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Heredity, historical perspectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79The Monk and his peas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Principle of segregation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80Dihybrid Crosses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Mutations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85Genetic Terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85The modern view of the gene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Interactions among genes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Polygenic inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Genes and chromosomes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90Chromosome abnormalities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91The physical carrier of inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92The structure of DNA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94DNA Replication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Protein Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99The structure of hemoglobin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101Transcription: making an RNA copy of a DNA sequence. . . . . . . . . . . . . . . . . . . . . . . . . 103Ecology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Population Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Mutualism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113Parasitism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113Commensalism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113Altering Population Growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115Range and Density. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Ecology Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Community Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Classification of Communities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117Change in Communities Over Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126Ecosystems and Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Biogeochemical Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 2
  3. 3. INTRODUCTION: THE NATURE OF SCIENCE AND BIOLOGYBiology: The Science of Our LivesBiology literally means "the study of life". Biology is such a broad field, covering the minute workings of chemicalmachines inside our cells, to broad scale concepts of ecosystems and global climate change. Biologists study intimatedetails of the human brain, the composition of our genes, and even the functioning of our reproductive system. Biologistsrecently all but completed the deciphering of the human genome, the sequence of deoxyribonucleic acid (DNA) bases thatmay determine much of our innate capabilities and predispositions to certain forms of behavior and illnesses. DNAsequences have played major roles in criminal cases (O.J. Simpson, as well as the reversal of death penalties for manywrongfully convicted individuals), as well as the impeachment of President Clinton. We are bombarded with headlinesabout possible health risks from favorite foods (Chinese, Mexican, hamburgers, etc.) as well as the potential benefits ofeating other foods such as cooked tomatoes. Infomercials tout the benefits of metabolism-adjusting drugs for weight loss.Many Americans are turning to herbal remedies to ease arthritis pain, improve memory, as well as improve our moods.Can a biology book give you the answers to these questions? No, but it will enable you learn how to sift through thebiases of investigators, the press, and others in a quest to critically evaluate the question. To be honest, five years after youare through with this class it is doubtful you would remember all the details of metabolism. However, you will knowwhere to look and maybe a little about the process of science that will allow you to make an informed decision. Will yoube a scientist? Yes, in a way. You may not be formally trained as a science major, but you can think critically, solveproblems, and have some idea about what science can and cannot do. I hope you will be able to tell the shoe from theshinola.Science and the Scientific MethodScience is an objective, logical, and repeatable attempt to understand the principles and forces operating in the naturaluniverse. Science is from the Latin word, scientia, to know. Good science is not dogmatic, but should be viewed as anongoing process of testing and evaluation. One of the hoped-for benefits of students taking a biology course is that theywill become more familiar with the process of science.Humans seem innately interested in the world we live in. Young children drive their parents batty with constant "why"questions. Science is a means to get some of those whys answered. When we shop for groceries, we are conducting a kindof scientific experiment. If you like Brand X of soup, and Brand Y is on sale, perhaps you try Brand Y. If you like it youmay buy it again, even when it is not on sale. If you did not like Brand Y, then no sale will get you to try it again.In order to conduct science, one must know the rules of the game (imagine playing Monopoly and having to discover therules as you play! Which is precisely what one does with some computer or videogames (before buying the cheat book).The scientific method is to be used as a guide that can be modified. In some sciences, such as taxonomy and certain typesof geology, laboratory experiments are not necessarily performed. Instead, after formulating a hypothesis, additionalobservations and/or collections are made from different localities.Steps in the scientific method commonly include: 1. Observation: defining the problem you wish to explain. 2. Hypothesis: one or more falsifiable explanations for the observation. 3. Experimentation: Controlled attempts to test one or more hypotheses. 4. Conclusion: was the hypothesis supported or not? After this step the hypothesis is either modified or rejected, which causes a repeat of the steps above.After a hypothesis has been repeatedly tested, a hierarchy of scientific thought develops. Hypothesis is the most common,with the lowest level of certainty. A theory is a hypothesis that has been repeatedly tested with little modification, e.g. TheTheory of Evolution. A Law is one of the fundamental underlying principles of how the Universe is organized, e.g. TheLaws of Thermodynamics, Newtons Law of Gravity. Science uses the word theory differently than it is used in the 3
  4. 4. general population. Theory to most people, in general nonscientific use, is an untested idea. Scientists call this ahypothesis.Scientific experiments are also concerned with isolating the variables. A good science experiment does not simultaneouslytest several variables, but rather a single variable that can be measured against a control. Scientific controlled experimentsare situations where all factors are the same between two test subjects, except for the single experimental variable.Consider a commonly conducted science fair experiment. Sandy wants to test the effect of gangsta rap music on pea plantgrowth. She plays loud rap music 24 hours a day to a series of pea plants grown under light, and watered every day. At theend of her experiment she concludes gangsta rap is conducive to plant growth. Her teacher grades her project very low,citing the lack of a control group for the experiment. Sandy returns to her experiment, but this time she has a separategroup of plants under the same conditions as the rapping plants, but with soothing Led Zeppelin songs playing. She comesto the same conclusion as before, but now has a basis for comparison. Her teacher gives her project a better grade.Theories Contributing to Modern BiologyModern biology is based on several great ideas, or theories: 1. The Cell Theory 2. The Theory of Evolution by Natural Selection 3. Gene Theory 4. HomeostasisRobert Hooke (1635-1703), one of the first scientists to use a microscope to examine pond water, cork and other things,referred to the cavities he saw in cork as "cells", Latin for chambers. Mattias Schleiden (in 1838) concluded all planttissues consisted of cells. In 1839, Theodore Schwann came to a similar conclusion for animal tissues. Rudolf Virchow, in1858, combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory. Thusthere is a chain-of-existence extending from your cells back to the earliest cells, over 3.5 billion years ago. The cell theorystates that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells. James Watson (L) and Francis Crick (R), and the model they built of the structure of deoxyribonucleic acid, DNA. While a model may seem a small thing, their development of the DNA model fostered increased understanding of how genes work. Image from the Internet.In 1953, American scientist James Watson and British scientist Francis Crick developed the model for deoxyribonucleicacid (DNA), a chemical that had (then) recently been deduced to be the physical carrier of inheritance. Crick hypothesizedthe mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the central dogma.Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" ofproteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins).Homeostasis is the maintenance of a dynamic range of conditions within which the organism can function. Temperature,pH, and energy are major components of this concept. Thermodynamics is a field of study that covers the laws governingenergy transfers, and thus the basis for life on earth. Two major laws are known: the conservation of matter and energy, 4
  5. 5. and entropy. These will be discussed in more detail in a later chapter. The universe is composed of two things: matter(atoms, etc.) and energy.These first three theories are very accepted by scientists and the general public. The theory of evolution is well acceptedby scientists and most of the general public. However, it remains a lightening rod for school boards, politicians, andtelevision preachers. Much of this confusion results from what the theory says and what it does not say.Development of the Theory of EvolutionModern biology is based on several unifying themes, such as the cell theory, genetics and inheritance, Francis Crickscentral dogma of information flow, and Darwin and Wallaces theory of evolution by natural selection. In this first unit wewill examine these themes and the nature of science.The Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman philosopher Lucretius (99-55 B.C.) coinedthe concept that all living things were related and that they had changed over time. The classical science of their time wasobservational rather than experimental. Another ancient Greek philosopher, Aristotle developed his Scala Naturae, orLadder of Life, to explain his concept of the advancement of living things from inanimate matter to plants, then animalsand finally man. This concept of man as the "crown of creation" still plagues modern evolutionary biologists. Post-Aristotlean "scientists" were constrained by the prevailing thought patterns of the Middle Ages -- the inerrancy ofthe biblical book of Genesis and the special creation of the world in a literal six days of the 24-hour variety. ArchbishopJames Ussher of Ireland, in the late 1600s calculated the age of the earth based on the genealogies from Adam and Evelisted in the biblical book of Genesis. According to Usshers calculations, the earth was formed on October 22, 4004 B.C.These calculations were part of Usshers book, History of the World. The chronology he developed was taken as factual,and was even printed in the front pages of bibles. Usshers ideas were readily accepted, in part because they posed nothreat to the social order of the times; comfortable ideas that would not upset the linked apple carts of church and state.Often new ideas must "come out of left field", appearing as wild notions, but in many cases prompting investigationwhich may later reveal the "truth". Usshers ideas were comfortable, the Bible was viewed as correct, therefore the earthmust be only 5000 years old.Geologists had for some time doubted the "truth" of a 5,000 year old earth. Leonardo da Vinci (painter of the Last Supper,and the Mona Lisa, architect and engineer) calculated the sedimentation rates in the Po River of Italy. Da Vinci concludedit took 200,000 years to form some nearby rock deposits. Galileo, convicted heretic for his contention that the Earth wasnot the center of the Universe, studied fossils (evidence of past life) and concluded that they were real and not inanimateartifacts. James Hutton, regarded as the Father of modern geology, developed the Theory of Uniformitarian’s, the basis ofmodern geology and paleontology. According to Huttons work, certain geological processes operated in the past in muchthe same fashion as they do today, with minor exceptions of rates, etc. Thus many geological structures and processescannot be explained if the earth was only a mere 5000 years old.The Modern View of the Age of the EarthRadiometric age assignments based on the rates of decay of radioactive isotopes, not discovered until the late 19thcentury, suggest the earth is over 4.5 billion years old. The Earth is thought older than 4.5 billion years, with the oldestknown rocks being 3.96 billion years old. Geologic time divides into eons, eras, and smaller units. The geologic time scale, highlighting some of the firsts in the evolution of life. One way to represent geological time. Note the break during the Precambrian. If the vertical scale was truly to scale the Precambrian would account for 7/8 of the graphic.Development of the modern view of Evolution 5
  6. 6. Erasmus Darwin (1731-1802; grandfather of Charles Darwin) a British physician and poet in the late 1700s, proposed thatlife had changed over time, although he did not present a mechanism. Georges-Louis Leclerc, Comte de Buffon(pronounced Bu-fone; 1707-1788) in the middle to late 1700s proposed that species could change. This was a major breakfrom earlier concepts that species were created by a perfect creator and therefore could not change because they wereperfect, etc.Swedish botanist Carl Linne (more popularly known as Linneus, after the common practice of the day which was toLatinize names of learned men), attempted to pigeon-hole all known species of his time (1753) into immutable categories.Many of these categories are still used in biology, although the underlying thought concept is now evolution and notimmutability of species. Linnean hierarchical classification was based on the premise that the species was the smallestunit, and that each species (or taxon) belonged to a higher category.Linnean Hierarchical for Classification of SpeciesKingdom AnimaliaPhylum (Division is used for plants) ChordataClass MammaliaOrder PrimatesFamily HominidaeGenus HomoSpecies sapiensPneumonic: King Phillip Crossed Over For Ginger Snaps Linneus also developed the concept of binomial nomenclature, whereby scientists speaking and writing different languages could communicate clearly. For example Man in English is Hombre in Spanish, Mensch in German, and Homo in Latin. Linneus settled on Latin, which was the language of learned men at that time. If a scientist refers to Homo, all scientists know what he or she means. William "Strata" Smith (1769-1839), employed by the English coal mining industry, developed the first accurate geologic map of England. He also, from his extensive travels, developed the Principle of Biological Succession. This idea states that each period of Earth history has its own unique assemblages of fossils. In essence Smith fathered the science of stratigraphy, the correlation of rock layers based on (among other things) their fossil contents. He also developedan idea that life had changed over time, but did not overtly state that.Abraham Gottlob Werner and Baron Georges Cuvier (1769-1832) were among the foremost proponents of catastrophism,the theory that the earth and geological events had formed suddenly, as a result of some great catastrophe (such as Noahsflood). This view was a comfortable one for the times and thus was widely accepted. Cuvier eventually proposed thatthere had been several creations that occurred after catastrophes. Louis Agassiz (1807-1873) proposed 50-80 catastrophesand creations.Jean Baptiste de Lamarck (1744-1829) developed one of the first theories on how species changed. He proposed theinheritance of acquired characteristics to explain, among other things, the length of the giraffe neck. The Lamarckian viewis that modern giraffes have long necks because their ancestors progressively gained longer necks due to stretching toreach food higher and higher in trees. According to the 19th century concept of use and disuse the stretching of necksresulted in their development, which was somehow passed on to their progeny. Today we realize that only bacteria areable to incorporate non-genetic (nonheritable) traits. Lamarcks work was a theory that plainly stated that life had changedover time and provided (albeit an erroneous) mechanism of change.Darwinian evolution 6
  7. 7. Charles Darwin, former divinity student and former medical student, secured (through the intercession of his geologyprofessor) an unpaid position as ships naturalist on the British exploratory vessel H.M.S. Beagle. The voyage wouldprovide Darwin a unique opportunity to study adaptation and gather a great deal of proof he would later incorporate intohis theory of evolution. On his return to England in 1836, Darwin began (with the assistance of numerous specialists) tocatalog his collections and ponder the seeming "fit" of organisms to their mode of existence. He eventually settled on fourmain points of a radical new hypothesis: 1. Adaptation: all organisms adapt to their environments. 2. Variation: all organisms are variable in their traits. 3. Over-reproduction: all organisms tend to reproduce beyond their environments capacity to support them (this is based on the work of Thomas Malthus, who studied how populations of organisms tended to grow geometrically until they encountered a limit on their population size). 4. Since not all organisms are equally well adapted to their environment, some will survive and reproduce better than others -- this is known as natural selection. Sometimes this is also referred to as "survival of the fittest". In reality this merely deals with the reproductive success of the organisms, not solely their relative strength or speed.Unlike the upper-class Darwin, Alfred Russel Wallace (1823-1913) came from a different social class. Wallace spentmany years in South America, publishing salvaged notes in Travels on the Amazon and Rio Negro in 1853. In 1854,Wallace left England to study the natural history of Indonesia, where he contracted malaria. During a fever Wallacemanaged to write down his ideas on natural selection.In 1858, Darwin received a letter from Wallace, in which Darwins as-yet-unpublished theory of evolution and adaptationwas precisely detailed. Darwin arranged for Wallaces letter to be read at a scientific meeting, along with a synopsis of hisown ideas. To be correct, we need to mention that both Darwin and Wallace developed the theory, although Darwinsmajor work was not published until 1859 (the book On the Origin of Species by Means of Natural Selection, consideredby many as one of the most influential books written). While there have been some changes to the theory since 1859, mostnotably the incorporation of genetics and DNA into what is termed the "Modern Synthesis" during the 1940s, mostscientists today acknowledge evolution as the guiding theory for modern biology.Recent revisions of biology curricula stressed the need for underlying themes. Evolution serves as such a universal theme.An excellent site devoted to Darwins thoughts and work is available by clicking here. At that same site is a timelineshowing many of the events mentioned above in their historical contexts. The Diversity of Life Evolutionary theory and the cell theory provide us with a basis for the interrelation of all living things. We also utilize Linneus hierarchical classification system, adopting (generally) five kingdoms of living organisms. Viruses, as discussed later, are not considered living.. Recent studies suggest that there might be a sixth Kingdom, the Archaea. A simple phylogenetic representation of three domains of life" Archaea, Bacteria (Eubacteria), and Eukaryota (all eukaryotic groups: Protista, Plantae, Fungi, and Animalia). 7
  8. 8. The Five Kingdoms. Methods of Kingdom Organization Environmental Significance Examples Nutrition Photosynthesis, Single-celled, Monerans play various roles in almost Bacteria (E. coli), chemosynthesis, filament, or colony all food chains, including cyanobacteria (Oscillatoria), decomposer, of cells; all producer,consumer, and decomposer. methanogens, and parasitic. prokaryotic. thermacidophiles.Monera Cyanobacteria are important oxygen producers.(in the broadest sense,including organisms Many Monerans also produce nitrogen,usually placed in the vitamins, antibiotics, and are importantDomain Archaea). compoents in human and animal intestines. Photosynthesis, Single-celled, Important producers in ocean/pond Plankton (both absorb food from filamentous, food chain. phytoplankton and environment, or colonial, and zooplankton), algae (kelp,Protista trap/engulf smaller multicelled; all Source of food in some human cultures. diatoms, dinoflagellates),and organisms. eukaryotic. Protozoa (Amoeba, Phytoplankton component that is one of Paramecium). the major producers of oxygen Absorb food from a Single-celled, Decomposer, parasite, and consumer. Mushrooms (Agaricus host or from their filamentous, to campestris, the commercial environment. multicelled; all Produce antibiotics,help make bread mushroom), molds,Fungi eukaryotic. and alcohol. mildews, rusts and smuts All heterotrophic. (plant parasites), yeasts Crop parasites (Dutch Elm Disease, (Saccharomyces cerevisae, Karnal Bunt, Corn Smut, etc.). the brewers yeast). Almost all All multicelled, Food source, medicines and drugs, Angiosperms (oaks, tulips, photosynthetic, photosynthetic, dyes, building material, fuel. cacti),gymnosperms (pines, although a few autotrophs.. spuce, fir), mosses,Plantae parasitic plants are Producer in most food chains. ferns,liverworts, horsetails known. (Equisetum, the scouring rush) All heterotrophic. Multicelled Consumer level in most food chains Sponges, worms,molluscs, heterotrophs (herbivores,carnivores,omnivores). insects, starfish,mammals, capable of amphibians,fish, birds,Animalia movement at some Food source, beasts of burden and reptiles, and dinosaurs, and stage during their transportation, recreation, and people. life history (even companionship. couch potatoes).Monera, the most primitive kingdom, contain living organisms remarkably similar to ancient fossils. Organisms in thisgroup lack membrane-bound organelles associated with higher forms of life. Such organisms are known as prokaryotes.Bacteria (technically the Eubacteria) and blue-green bacteria (sometimes called blue-green algae, or cyanobacteria) are themajor forms of life in this kingdom. The most primitive group, the archaebacteria, are today restricted to marginal habitatssuch as hot springs or areas of low oxygen concentration. 8
  9. 9. Protista were the first of the eukaryotic kingdoms, these organisms and all others have membrane-bound organelles,which allow for compartmentalization and dedication of specific areas for specific functions. The chief importance ofProtista is their role as a stem group for the remaining Kingdoms: Plants, Animals, and Fungi. Major groups within theProtista include the algae, euglenoids, ciliates, protozoa, and flagellates. Scanning electron micrographs of diatoms (Protista).There are two basic types of diatoms: bilaterally symmetrical (left) and radially symmetrical (right). Light micrographs of some protistans.Fungi are almost entirely multicellular (with yeast, Saccharomyces cerviseae, being a prominent unicellular fungus),heterotrophic (deriving their energy from another organism, whether alive or dead), and usually having some cells withtwo nuclei (multinucleate, as opposed to the more common one, or uninucleate) per cell. Ecologically this kingdom isimportant (along with certain bacteria) as decomposers and recyclers of nutrients. Economically, the Fungi provide uswith food (mushrooms; Bleu cheese/Roquefort cheese; baking and brewing), antibiotics (the first of the wonder drugs,penicillin, was isolated from a fungus Penicillium), and crop parasites (doing several billion dollars per year of damage).Plantae include multicelled organisms that are all autotrophic (capable of making their own food by the process ofphotosynthesis, the conversion of sunlight energy into chemical energy). Ecologically, this kingdom is generally (alongwith photosynthetic organisms in Monera and Protista) termed the producers, and rest at the base of all food webs. A foodweb is an ecological concept to trace energy flow through an ecosystem. Economically, this kingdom is unparalleled, withagriculture providing billions of dollars to the economy (as well as the foundation of "civilization"). Food, buildingmaterials, paper, drugs (both legal and illegal), and roses, are plants or plant-derived products.Animalia consists entirely of multicellular heterotrophs that are all capable (at some point during their life history) ofmobility. Ecologically, this kingdom occupies the level of consumers, which can be subdivided into herbivore (eaters ofplants) and carnivores (eaters of other animals). Humans, along with some other organisms, are omnivores (capable offunctioning as herbivores or carnivores). Economically, animals provide meat, hides, beasts of burden, pleasure (pets),transportation, and scents (as used in some perfumes). 9
  10. 10. Characteristics of living thingsLiving things have a variety of common characteristics. • Organization. Living things exhibit a high level of organization, with multicellular organisms being subdivided into cells, and cells into organelles, and organelles into molecules, etc. • Homeostasis. Homeostasis is the maintenance of a constant (yet also dynamic) internal environment in terms of temperature, pH, water concentrations, etc. Much of our own metabolic energy goes toward keeping within our own homeostatic limits. If you run a high fever for long enough, the increased temperature will damage certain organs and impair your proper functioning. Swallowing of common household chemicals, many of which are outside the pH (acid/base) levels we can tolerate, will likewise negatively impact the human bodys homeostatic regime. Muscular activity generates heat as a waste product. This heat is removed from our bodies by sweating. Some of this heat is used by warm-blooded animals, mammals and birds, to maintain their internal temperatures. • Adaptation. Living things are suited to their mode of existence. Charles Darwin began the recognition of the marvelous adaptations all life has that allow those organisms to exist in their environment. • Reproduction and heredity. Since all cells come from existing cells, they must have some way of reproducing, whether that involves asexual (no recombination of genetic material) or sexual (recombination of genetic material). Most living things use the chemical DNA (deoxyribonucleic acid) as the physical carrier of inheritance and the genetic information. Some organisms, such as retroviruses (of which HIV is a member), use RNA (ribonucleic acid) as the carrier. The variation that Darwin and Wallace recognized as the wellspring of evolution and adaptation, is greatly increased by sexual reproduction. • Growth and development. Even single-celled organisms grow. When first formed by cell division, they are small, and must grow and develop into mature cells. Multicellular organisms pass through a more complicated process of differentiation and organogenesis (because they have so many more cells to develop). • Energy acquisition and release. One view of life is that it is a struggle to acquire energy (from sunlight, inorganic chemicals, or another organism), and release it in the process of forming ATP (adenosine triphosphate). • Detection and response to stimuli (both internal and external). • Interactions. Living things interact with their environment as well as each other. Organisms obtain raw materials and energy from the environment or another organism. The various types of symbioses (organismal interactions with each other) are examples of this.Levels of OrganizationBiosphere: The sum of all living things taken in conjunction with their environment. In essence, where life occurs, fromthe upper reaches of the atmosphere to the top few meters of soil, to the bottoms of the oceans. We divide the earth intoatmosphere (air), lithosphere (earth), hydrosphere (water), and biosphere (life). Ecosystem: The relationships of a smaller groups of organisms with each other and their environment. Scientists often speak of the interrelatedness of living things. Since, according to Darwins theory, organisms adapt to their environment, they must also adapt to other organisms in that environment. We can discuss the flow of energy through an ecosystem from photosynthetic autotrophs to herbivores to carnivores. Community: The relationships between groups of different species. For example, the desert communities consist of rabbits, coyotes, snakes, birds, miceand such plants as sahuaro cactus (Carnegia gigantea), Ocotillo, creosote bush, etc. Community structure can be disturbedby such things as fire, human activity, and over-population.Species: Groups of similar individuals who tend to mate and produce viable, fertile offspring. We often find speciesdescribed not by their reproduction (a biological species) but rather by their form (anatomical or form species). 10
  11. 11. Populations: Groups of similar individuals who tend to mate with each other in a limited geographic area. This can be assimple as a field of flowers, which is separated from another field by a hill or other area where none of these flowersoccur.Individuals: One or more cells characterized by a unique arrangement of DNA "information". These can be unicellular ormulticellular. The multicellular individual exhibits specialization of cell types and division oflabor into tissues, organs, and organ systems.Organ System: (in multicellular organisms). A group of cells, tissues, and organs that perform aspecific major function. For example: the cardiovascular system functions in circulation ofblood.Organ: (in multicellular organisms). A group of cells or tissues performing an overall function.For example: the heart is an organ that pumps blood within the cardiovascular system. Tissue: (in multicellular organisms). A group of cells performing a specific function. For example heart muscle tissue is found in the heart and its unique contraction properties aid the hearts functioning as a pump. . Cell: The fundamental unit of living things. Each cell has some sort of hereditary material (either DNA or more rarely RNA), energy acquiring chemicals, structures, etc. Living things, by definition, must have the metabolic chemicals plus a nucleic acid hereditary information molecule.Organelle: A subunit of a cell, an organelle is involved in a specific subcellularfunction, for example the ribosome (the site of protein synthesis) ormitochondrion (the site of ATP generation in eukaryotes).Molecules, atoms, and subatomic particles: The fundamental functional levels ofbiochemistry.It is thus possible to study biology at many levels, from collections of organisms (communities), to the inner workings ofa cell (organelle).Learning Objectives • Name the special molecule that sets living things apart from the nonliving world and be able to explain why this molecule is important. • The cell is considered to be the basic living unit. Be able to distinguish between single-celled organisms and multicelled organisms. • Be able to arrange in order, from smallest to largest, the levels of organization that occur in nature and to write a brief description of each. • What does the term metabolism mean to the cell and the organism. • Organisms use a molecule known as ATP to transfer chemical energy from one molecule to another. Why is this essential for living things to exist. • Homeostasis is defined as a state in which the conditions of an organisms internal environment are maintained within tolerable limits. What mechanisms in your body are involved with homeostasis? • Reproduction is the means by which each new organism arises. Why is this an essential characteristic of life? • How are DNA and cellular reproduction linked in the process of inheritance? • A trait that assists an organism in survival and reproduction in a certain environment is said to be adaptive. What sorts of adaptive traits do you have? How do they aid your survival? • List the five kingdoms of life that are currently recognized by most scientists; tell generally what kinds of organisms are classified in each kingdom, and discuss the new ideas about Domains and how they may alter the five kingdom approach. 11
  12. 12. • Arrange in order, from the fewer to the greater numbers of organisms included, the following categories of classification: class, family, genus, kingdom, order, phylum, and species. • Explain what the term biological diversity means to you, and speculate about what caused the great diversity of life on Earth. • Define natural selection and briefly describe what is occurring when a population is said to evolve. • Outline a set of steps that might be used in the scientific method of investigating a problem. • Explain why a control group is used in an experiment. • Define what is meant by a theory; cite an actual example that is significant to biology.Review Questions 1. Which of these scientific terms has the greatest degree of certainty? a) hypothesis; b) theory; c) law; d) guess. 2. The purpose of a control in a scientific experiment is to ___. a) provide a basis of comparison between experimental and nonexperimental; b) indicate the dependent variable; c) indicate the independent variable; d) provide a baseline from which to graph the data. 3. Which of these theories is not a basis for modern biology? a) evolution; b) creationism; c) cell theory; d) gene theory. 4. The molecule that is the physical carrier of inheritance is known as ___. a) ATP; b) RNA; c) DNA; d) NADH 5. Bacteria belong to the taxonomic kingdom ____. a) Plantae; b) Protista; c) Animalia; d) Fungi; e) Monera 6. Mushrooms belong to which of these taxonomic kingdoms? a) Plantae; b) Protista; c) Animalia; d) Fungi; e) Monera 7. Papaver somniferum, the opium poppy, belongs to which of these taxonomic kingdoms? a) Plantae; b) Protista; c) Animalia; d) Fungi; e) Monera 8. The sum of all energy transfers within a cell is known as _____. a) photosynthesis; b) cellular respiration; c) metabolism; d) replication; e) conjugation. 9. The molecule that is the energy coin of the cell is ___. a) ATP; b) RNA; c) DNA; d) NADH 10. Which of these is NOT a living organism? a) cactus; b) cat; c) algae; d) virus; e) yeast 11. Which of the following is the least inclusive (smallest) unit of classification? a) kingdom; b) species; c) genus; d) class; e) phylum 12. The scientist(s) credited with developing the theory of evolution by natural selection were ____. a) James Watson and Francis Crick; b) Aristotle and Lucretius; c) Charles Darwin and Alfred Wallace; d) Robert Hooke and Rudolph Virchow; e) James Watson and Charles Darwin 13. When an organism consists of a single cell, the organism is referred to as ___. a) uninucleate; b) uniport; c) unisexual; d) unicellular 14. According to science, the Earth is ___ years old. a) 4.5 billion; b) 4.5 million; c) 10 billion; d) 10,000; e) 450 million 15. Which of these is not an economic use of bacteria? a) food; b) biotechnology; c) mushrooms; d) food spoilage 12
  13. 13. WATER AND ORGANIC MOLECULESStructure of WaterIt can be quite correctly argued that life exists on Earth because of the abundant liquid water. Other planets havewater, but they either have it as a gas (Venus) or ice (Mars). Recent studies of Mars reveal the presencesometime in the past of running fluid, possibly water. The chemical nature of water is thus one we mustexamine as it permeates living systems: water is auniversal solvent, and can be too much of a goodthing for some cells to deal with.Water is polar covalently bonded within themolecule. This unequal sharing of the electronsresults in a slightly positive and a slightly negativeside of the molecule. Other molecules, such asEthane, are nonpolar, having neither a positive nor anegative side.The difference between a polar (water) andnonpolar (ethane) molecule is due to the unequalsharing of electrons within the polar molecule.Nonpolar molecules have electrons equally sharedwithin their covalent bonds.These link up by the hydrogen bond discussed earlier. Consequently, water has a great interconnectivity ofindividual molecules, which is caused by the individually weak hydrogen bonds, that can be quite strong whentaken by the billions.Water has been referred to as the universal solvent. Living things are composed of atoms and molecules withinaqueous solutions (solutions that have materials dissolved in water). Solutions are uniform mixtures of themolecules of two or more substances. The solvent isusually the substance present in the greatest amount (andis usually also a liquid). The substances of lesser amountsare the solutes.The solubility of many molecules is determined by theirmolecular structure. You are familiar with the phrase"mixing like oil and water." The biochemical basis forthis phrase is that the organic macromolecules known as 13
  14. 14. lipids (of which fats are an important, although often troublesome, group) have areas that lack polar covalentbonds. The polar covalently bonded water molecules act to exclude nonpolar molecules, causing the fats toclump together. The structure of many molecules can greatly influence their solubility. Sugars, such as glucose,have many hydroxyl (OH) groups, which tend to increase the solubility of the molecule.Water tends to disassociate into H+ and OH- ions. In this disassociation, the oxygen retains the electrons andonly one of the hydrogens, becoming a negatively charged ion known as hydroxide. Pure water has the samenumber (or concentration) of H+ as OH- ions. Acidic solutions have more H+ ions than OH- ions. Basic solutionshave the opposite. An acid causes an increase in the numbers of H+ ions and a base causes an increase in thenumbers of OH- ions.The pH scale is a logarithmic scale representing the concentration of H+ ions in a solution. Remember that asthe H+ concentration increases the OH- concentration decreases and vice versa . If we have a solution with onein every ten molecules being H+, we refer to the concentration of H+ ions as 1/10. Remember from algebra thatwe can write a fraction as a negative exponent, thus 1/10 becomes 10-1. Conversely 1/100 becomes 10-2 , 1/1000becomes 10-3, etc. Logarithms are exponents to which a number (usually 10) has been raised. For example log10 (pronounced "the log of 10") = 1 (since 10 may be written as 101). The log 1/10 (or 10-1) = -1. pH, a measureof the concentration of H+ ions, is the negative log of the H+ ion concentration. If the pH of water is 7, then theconcentration of H+ ions is 10-7, or 1/10,000,000. In the case of strong acids, such as hydrochloric acid (HCl), anacid secreted by the lining of your stomach, [H+] (the concentration of H+ ions, written in a chemical shorthand)is 10-1; therefore the pH is 1.Organic moleculesOrganic molecules are those that: 1) formed by the actions of living things; and/or 2) have a carbon backbone.Methane (CH4) is an example of this. If we remove the H from one of the methane units below, and begin 14
  15. 15. linking them up, while removing other H units, we begin toform an organic molecule. (NOTE: Not all methane isorganically derived, methane is a major component of theatmosphere of Jupiter, which we think is devoid of life).When two methanes are combined, the resultant moleculeis Ethane, which has a chemical formula C2H6. Moleculesmade up of H and C are known as hydrocarbons.Scientists eventually realized that specific chemicalproperties were a result of the presence of particularfunctional groups. Functional groups are clusters of atoms with characteristic structure and functions. Polar molecules (with +/- charges) are attracted to water molecules and are hydrophilic. Nonpolar molecules are repelled by water and do not dissolve in water; are hydrophobic. Hydrocarbon is hydrophobic except when it has an attached ionized functional group such as carboxyl (acid) (COOH), then molecule is hydrophilic. Since cells are 70-90% water, the degree to which organic molecules interact with water affects their function. One of the most common groups is the -OH (hydroxyl) group. Its presence will enable a molecule to be water soluble.Isomers are molecules with identical molecular formulas but differ in arrangement of their atoms (e.g.,glyceraldehyde and dihydroxyacetone)..Functional groups in organic molecules. 15
  16. 16. Carbon has four electrons in outer shell, and can bond with up to four other atoms (usually H, O, N, or anotherC). Since carbon can make covalent bonds with another carbon atom, carbon chains and rings that serve as thebackbones of organic molecules are possible.Chemical bonds store energy. The C-C covalent bond has 83.1 Kcal (kilocalories) per mole, while the C=Cdouble covalent bond has 147 Kcal/mole. Energy is in two forms: kinetic, or energy in use/motion; andpotential, or energy at rest or in storage. Chemical bonds are potential energy, until they are converted intoanother form of energy, kinetic energy (according to the two laws of thermodynamics).Each organic molecule group has small molecules (monomers) that are linked to form a larger organic molecule(macromolecule). Monomers can be joined together to form polymers that are the large macromolecules madeof three to millions of monomer subunits.Macromolecules are constructed by covalently bonding monomers by condensation reactions where water isremoved from functional groups on the monomers. Cellular enzymes carry out condensation (and the reversal ofthe reaction, hydrolysis of polymers). Condensation involves a dehydration synthesis because a water isremoved (dehydration) and a bond is made (synthesis). When two monomers join, a hydroxyl (OH) group isremoved from one monomer and a hydrogen (H) is removed from the other. This produces the water given offduring a condensation reaction. Hydrolysis (hydration) reactions break down polymers in reverse ofcondensation; a hydroxyl (OH) group from water attaches to one monomer and hydrogen (H) attaches to theother. 16
  17. 17. There are four classes of macromolecules (polysaccharides, triglycerides, polypeptides, nucleic acids). Theseclasses perform a variety of functions in cells.1. Carbohydrates have the general formula [CH2O]n where n is a number between 3 and 6.. Carbohydratesfunction in short-term energy storage (such as sugar); as intermediate-term energy storage (starch for plants andglycogen for animals); and as structural components in cells (cellulose in the cell walls of plants and manyprotists), and chitin in the exoskeleton of insects and other arthropods.Sugars are structurally the simplest carbohydrates. They are the structural unit which makes up the other typesof carbohydrates. Monosaccharides are single (mono=one) sugars. Important monosaccharides include ribose(C5H10O5), glucose (C6H12O6), and fructose (same formula but different structure than glucose).We classify monosaccharides by the number of carbon atoms and the types of functional groups present in thesugar. For example, glucose and fructose, have the same chemical formula (C6H12O6), but a different structure:glucose having an aldehyde (internal hydroxyl shown as: -OH) and fructose having a keto group (internaldouble-bond O, shown as: =O). This functional group difference, as small as it seems, accounts for the greatersweetness of fructose as compared to glucose. 17
  18. 18. In an aqueous solution, glucose tends to have two structures, α (alpha) and β (beta), with an intermediatestraight-chain form. The α form and β form differ in the location of one -OH group. Glucose is a commonhexose, six carbon sugar, in plants. The products of photosynthesis are assembled to form glucose. Energy fromsunlight is converted into and stored as C-C covalent bond energy. This energy is released in living organismsin such a way that not enough heat is generated at once to incinerate the organisms. One mole of glucose yields673 Kcal of energy. (A calorie is the amount of heat needed to raise one gram of water one degree C. A Kcalhas 1000 times as much energy as a cal.). Glucose is also the form of sugar measured in the humanbloodstream. Monosaccarides: Glucose, Fructose, Galactose, Ribose, and Deoxyribose Disaccharides are formed when two monosaccharides are chemically bonded together. Sucrose, a common plant disaccharide is composed of the monosaccharides glucose and fructose. Lactose, milk sugar, is a disaccharide composed of glucose and the monosaccharide galactose. The maltose that flavors a maltedmilkshake (and other items) is also a disaccharide made of two glucose molecules bonded together as shown in.Polysaccharides are large molecules composed of individual monosaccharide units. A common plantpolysaccharide is starch which is made up of many glucoses (in a polypeptide these are referred to as glucans).Two forms of polysaccharide, amylose and amylopectin makeup what we commonly call starch. The formationof the ester bond by condensation (the removal of water from a molecule) allows the linking ofmonosaccharides into disaccharides and polysaccharides. Glycogen is an animal storage product thataccumulates in the vertebrate liver. 18
  19. 19. Cellulose, is a polysaccharide found in plant cell walls. Cellulose forms the fibrous part of the plant cell wall. Interms of human diets, cellulose is indigestible, and thus forms an important, easily obtained part of dietary fiber. As compared to starch and glycogen, which are each made up of mixtures of α and β glucoses, cellulose (and the animal structural polysaccharide chitin) are made up of only β glucoses. The three-dimensional structure of these polysaccharides is thus constrained into straight microfibrils by the uniform nature of the glucoses, which resist the actions of enzymes (such as amylase) that breakdown storage polysaccharides (such a starch).2. Lipids are involved mainly with long-term energy storage. They are generally insoluble in polar substancessuch as water. Secondary functions of lipids include structural components (as in the case of phospholipids thatare the major building block in cell membranes) and "messengers" (hormones) that play roles incommunications within and between cells. Lipids are composed of three fatty acids (usually) covalently bondedto a 3-carbon glycerol. The fatty acids are composed of CH2 units, and are hydrophobic/not water soluble.Fatty acids can be saturated (meaning they have as many hydrogens bonded to their carbons as possible) orunsaturated (with one or more double bonds connecting their carbons, hence fewer hydrogens). A fat is solid atroom temperature, while an oil is a liquid under the same conditions. The fatty acids in oils are mostlyunsaturated, while those in fats are mostly saturated.Saturated (palmitic and stearic) and unsaturated (next page Oleic) fatty acids. The term saturated refers to the"saturation" of the molecule by hydrogen atoms. The presence of a double C=C covalent bond reduces thenumber of hydrogens that can bond to the carbon chain, hence the application of therm "unsaturated". 19
  20. 20. Fats and oils function in long-term energy storage. Animals convert excess sugars (beyond their glycogenstorage capacities) into fats. Most plants store excess sugars as starch, although some seeds and fruits haveenergy stored as oils (e.g. corn oil, peanut oil, palm oil, canola oil, and sunflower oil). Fats yield 9.3 Kcal/gm,while carbohydrates yield 3.79 Kcal/gm. Fats thus store six times as much energy as glycogen.Diets are attempts to reduce the amount of fats present in specialized cells known as adipose cells thataccumulate in certain areas of the human body. By restricting the intakes of carbohydrates and fats, the body isforced to draw on its own stores to makeup the energy debt. The body responds to this by lowering its metabolicrate, often resulting in a drop of "energy level." Successful diets usually involve three things: decreasing theamounts of carbohydrates and fats; exercise; and behavior modification.Another use of fats is as insulators and cushions. The human body naturally accumulates some fats in the"posterior" area. Subdermal ("under the skin") fat plays a role in insulation.Phospholipids and glycolipids are important structural components of cell membranes. Phospholipids, aremodified so that a phosphate group (PO4-) is added to one of the fatty acids. The addition of this group makes apolar "head" and two nonpolar "tails". Waxes are an important structural component for many organisms, suchas the cuticle, a waxy layer covering the leaves and stems of many land plants; and protective coverings on skinand fur of animals.Cholesterol and steroids: Most mention of these two types of lipids in the news is usually negative.Cholesterol, has many biological uses, it occurs in cell membranes, and its forms the sheath of some types ofnerve cells. However, excess cholesterol in the blood has been linked to atherosclerosis, hardening of thearteries. Recent studies suggest a link between arterial plaque deposits of cholesterol, antibodies to thepneumonia-causing form of Chlamydia, and heart attacks. The plaque increases blood pressure, much the wayblockages in plumbing cause burst pipes in old houses.Structure of four steroids.. 20
  21. 21. 3. Proteins are very important in biological systems as control and structural elements. Control functions ofproteins are carried out by enzymes and proteinaceous hormones. Enzymes are chemicals that act as organiccatalysts (a catalyst is a chemical that promotes but is not changed by a chemical reaction). Structural proteinsfunction in the cell membrane, muscle tissue, etc.The building block of any protein is the amino acid, which has anamino end (NH2) and a carboxyl end (COOH). The R indicatesthe variable component (R-group) of each amino acid. Alanineand Valine, for example, are both nonpolar amino acids, but theydiffer, as do all amino acids, by the composition of their R-groups. All living things (and even viruses) use variouscombinations of the same twenty amino acids. A very powerfulbit of evidence for the phylogenetic connection of all livingthings. 21
  22. 22. Amino acids are linked together by joining the amino end of one molecule to the carboxyl end of another.Removal of water allows formation of a type of covalent bond known as a peptide bond.Formation of a peptide bond between two amino acids by the condensation (dehydration) of the amino end ofone amino acid and the acid end of the other amino acid.Amino acids are linked together into a polypeptide, the primary structure in the organization of proteins. Theprimary structure of a protein is the sequence of amino acids, which is directly related to the sequence ofinformation in the RNA molecule, which in turn is a copy of the information in the DNA molecule. Changes inthe primary structure can alter the proper functioning of the protein. Protein function is usually tied to theirthree-dimensional structure. The primary structure is the sequence of amino acids in a polypeptide..The secondary structure is the tendency of the polypeptide to coil or pleat due to H-bonding between R-groups.The tertiary structure is controlled by bonding (or in some cases repulsion) between R-groups.. Many proteins,such as hemoglobin, are formed from one or more polypeptides. Such structure is termed quaternary structure.Structural proteins, such as collagen, have regular repeated primary structures. Like the structuralcarbohydrates, the components determine the final shape and ultimately function. Collagens have a variety offunctions in living things, such as the tendons, hide, and corneas of a cow. Keratin is another structural protein.It is found in fingernails, feathers, hair, and rhinoceros horns. Microtubules, important in cell division andstructures of flagella and cilia (among other things), are composed of globular structural proteins.4. Nucleic acids are polymers composed of monomer units known as nucleotides. There are a very fewdifferent types of nucleotides. The main functions of nucleotides are information storage (DNA), proteinsynthesis (RNA), and energy transfers (ATP and NAD). Nucleotides, consist of a sugar, a nitrogenous base, anda phosphate. The sugars are either ribose or deoxyribose. They differ by the lack of one oxygen in deoxyribose.Both are pentoses usually in a ring form. There are five nitrogenous bases. Purines (Adenine and Guanine) aredouble-ring structures, while pyrimidines (Cytosine, Thymine and Uracil) are single-ringed. 22
  23. 23. Deoxyribonucleic acid (better known as DNA) is the physical carrier of inheritance for 99% of livingorganisms. The bases in DNA are C, G, A and T.Structure of a segment of a DNA double helix.DNA functions in information storage. The English alphabet has 26 letters that can be variously combined toform over 50,000 words. DNA has four letters (C, G, A, and T, the nitrogenous bases) that code for twentywords (the twenty amino acids found in all living things) that can make an infinite variety of sentences(polypeptides). Changes in the sequences of these bases information can alter the meaning of a sentence.For example take the sentence: I saw Elvis. This implies certain knowledge (that Ive been out in the sun toolong without a hat, etc.).If we alter the sentence by inverting the middle word, we get: I was Elvis (thank you, thank you very much).Now we have greatly altered the information.A third alteration will change the meaning: I was Levis. Clearly the original sentences meaning is now greatlychanged.Changes in DNA information will be translated into changes in the primary structure of a polypeptide, and fromthere to the secondary and tertiary structures. A mutation is any change in the DNA base sequence. Mostmutations are harmful, few are neutral, and a very few are beneficial and contribute the organisms reproductivesuccess. Mutations are the wellspring of variation, variation is central to Darwin and Wallaces theory ofevolution by natural selection.Ribonucleic acid (RNA), was discovered after DNA. DNA, with exceptions in chloroplasts and mitochondria, isrestricted to the nucleus (in eukaryotes, the nucleoid region in prokaryotes). RNA occurs in the nucleus as wellas in the cytoplasm (also remember that it occurs as part of the ribosomes that line the rough endoplasmicreticulum). There are three types of RNA: 23
  24. 24. Messenger RNA (mRNA) is the blueprint for construction of a protein.Ribosomal RNA (rRNA) is the construction site where the protein is made.Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time.Adenosine triphosphate, better known as ATP the energy currency or coin of the cell, transfers energy fromchemical bonds to endergonic (energy absorbing) reactions within the cell. Structurally, ATP consists of theadenine nucleotide (ribose sugar, adenine base, and phosphate group, PO4-2) plus two other phosphate groups.Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy (approximately7 kcal/mole) in the bond between the second and third phosphate groups. This covalent bond is known as apyrophosphate bond.Learning Objectives • Dissolved substances are called solutes; a fluid in which one or more substances can dissolve is called a solvent. Describe several solutions that you use everyday in terms of what is the solvent and what is the solute. • Define acid and base and be able to cite an example of each. • The concentration of free hydrogen ions in solutions is measured by the pH scale.. • Nearly all large biological molecules have theory organization influenced by interactions with water. Describe this interaction as it exists with carbohydrate molecules. • Be able to list the three most abundant elements in living things. • Each carbon atom can form as many as four covalent bonds with other carbon atoms as well as with other elements. Be able to explain why this is so. • Be able to list the four main groups of organic molecules and their functions in living things. • Enzymes are a special class of proteins that speed up chemical reactions in cells. What about the structure of proteins allows for the reaction specificity that occurs with most enzymes. • Condensation reactions result in the formation of covalent bonds between small molecules to form larger organic molecules. Be able to describe a condensation reaction in words. • Be able to describe what occurs during a hydrolysis reaction. • Be able to define carbohydrates and list their functions. • The simplest carbohydrates are sugar monomers, the monosaccharides. Be able to give examples and their functions. • A polysaccharide is a straight or branched chain of hundreds or thousands of sugar monomers, of the same or different kinds. Be able to give common examples and their functions. • Be able to define lipids and to list their functions. • Distinguish between a saturated fat and an unsaturated fat. Why is such a distinction a life and death matter for many people? • A phospholipid has two fatty acid tails attached to a glycerol backbone. What is the importance of these molecules. • Define steroids and describe their chemical structure. Be able to discuss the importance of the steroids known as cholesterol and hormones. • Be able to describe proteins and cite their general functions. • Be prepared to make a sketch and name the three parts of every amino acid. 24
  25. 25. • Describe the complex structure of a protein through its primary, secondary, tertiary, and quaternary structure. How does this relate to the three-dimensional structure of proteins? • Describe the three parts of every nucleotide.. • Be able to give the general functions of DNA and RNA molecules.Review Questions 1. The chemical reaction where water is removed during the formation of a covalent bond linking two monomers is known as ___. a) dehydration; b) hydrolysis; c) photosynthesis; d) protein synthesis 2. The monomer that makes up polysaccharides is ____. a) amino acids; b) glucose; c) fatty acids; d) nucleotides; e) glycerol 3. Proteins are composed of which of these monomers? a) amino acids; b) glucose; c) fatty acids; d) nucleotides; e) glycerol 4. Which of these is not a function of lipids? a) long term energy storage; b) structures in cells; c) hormones; d) enzymes; e) sex hormones 5. All living things use the same ___ amino acids. a) 4; b) 20; c) 100; d) 64 6. The sequence of ___ bases determines the ___ structure of a protein. a) RNA, secondary; b) DNA, quaternary; c) DNA, primary; d) RNA, primary 7. Which of these is not a nucleotide base found in DNA? a) uracil; b) adenine; c) guanine; d) thymine; e) cytosine 8. Which of these carbohydrates constitutes the bulk of dietary fiber? a) starch; b) cellulose; c) glucose; d) fructose; e) chitin 9. A diet high in _____ is considered unhealthy, since this type of material is largely found in animal tissues. a) saturated fats; b) testosterone; c) unsaturated fats; d) plant oils 10. The form of RNA that delivers information from DNA to be used in making a protein is ____. a) messenger RNA; b) ribosomal RNA; c) transfer RNA; d) heterogeneous nuclear RNA 11. The energy locked inside an organic molecule is most readily accessible in a ___ molecule. a) fat; b) DNA; c) glucose; d) chitin; e) enzyme 12. Phospholipids are important components in ____. a) cell walls; b) cytoplasm; c) DNA; d) cell membranes; e) cholesterol 25
  26. 26. CELLS: ORIGINSOrigin of the Earth and LifeScientific estimates place the origin of the Universe at between 10 and 20 billion years ago. The theory currently with themost acceptance is the Big Bang Theory, the idea that all matter in the Universe existed in a cosmic egg (smaller than thesize of a modern hydrogen atom) that exploded, forming the Universe. Recent discoveries from the Space Telescope andother devices suggest this theory may need some modification. Evidence for the Big Bang includes:1) The Red Shift: when stars/galaxies are moving away from us the energy they emit is shifted to the red side of thevisible-light spectrum. Those moving towards us are shifted to the violet side. This shift is an example of the Dopplereffect. Similar effects are observed when listening to a train whistle-- it will sound higher (shorter wavelengths)approaching and lower (longer wavelengths) as it moves away. Likewise red wavelengths are longer than violet ones.Most galaxies appear to be moving away from ours.2) Background radiation: two Bell Labs scientists discovered that in interstellar space there is a slight backgroundradiation, thought to be the residual after blast remnant of the Big Bang.Soon after the Big Bang the major forces (such as gravity, weak nuclear force, strong nuclear force, etc.) differentiated.While in the cosmic egg, scientists think that matter and energy as we understand them did not exist, but rather theyformed soon after the bang. After 10 million to 1 billion years the universe became clumpy, with matter beginning toaccumulate into solar systems. One of those solar systems, ours, began to form approximately 5 billion years ago, with alarge "protostar" (that became our sun) in the center. The planets were in orbits some distance from the star, theirincreasing gravitational fields sweeping stray debris into larger and larger planetesimals that eventually formed planets.The processes of radioactive decay and heat generated by the impact of planetesimals heated the Earth, which then beganto differentiate into a "cooled" outer cooled crust (of silicon, oxygen and other relatively light elements) and increasinglyhotter inner areas (composed of the heavier and denser elements such as iron and nickel). Impact (asteroid, comet,planetismals) and the beginnings of volcanism released water vapor, carbon dioxide, methane, ammonia and other gasesinto a developing atmosphere. Sometime "soon" after this, life on Earth began.Where did life originate and how?Extra-terrestrial: In 1969, a meteorite (left-over bits from the origin of the solar system) landed near Allende, Mexico.The Allende Meteorite (and others of its sort) have been analyzed and found to contain amino acids, the building blocks ofproteins, one of the four organic molecule groups basic to all life. The idea of panspermia hypothesized that life originatedout in space and came to Earth inside a meteorite. Recently, this idea has been revived as Cosmic Ancestry. The aminoacids recovered from meteorites are in a group known as exotics: they do not occur in the chemical systems of livingthings. The ET theory is now not considered by most scientists to be correct, although the August 1996 discovery of theMartian meteorite and its possible fossils have revived thought of life elsewhere in the Solar System.Supernatural: Since science is an attempt to measure and study the natural world, this theory is outside science (at leastour current understanding of science). Science classes deal with science, and this idea is in the category of not-science.Organic Chemical Evolution: Until the mid-1800s scientists thought organic chemicals (those with a C-C skeleton)could only form by the actions of living things. A French scientist heated crystals of a mineral (a mineral is by definitioninorganic), and discovered that they formed urea (an organic chemical) when they cooled. Russian scientist andacademician A.I. Oparin, in 1922, hypothesized that cellular life was preceded by a period of chemical evolution. Thesechemicals, he argued, must have arisen spontaneously under conditions existing billions of years ago (and quite unlikecurrent conditions). 26
  27. 27. In 1950, then-graduate student Stanley Miller designed an experimental test for Oparins hypothesis. Oparins originalhypothesis called for : 1) little or no free oxygen (oxygen not bonded to other elements); and 2) C H O and N inabundance. Studies of modern volcanic eruptions support inference of the existence of such an atmosphere. Millerdischarged an electric spark into a mixture thought to resemble the primordial composition of the atmosphere. From thewater receptacle, designed to model an ancient ocean, Miller recovered amino acids. Subsequent modifications of theatmosphere have produced representatives or precursors of all four organic macromolecular classes.. The primordial Earth was a very different place than today, with greater amounts of energy, stronger storms, etc. The oceans were a "soup" of organic compounds that formed by inorganic processes (although this soup would not taste umm ummm good). Millers (and subsequent) experiments have not proven life originated in this way, only that conditions thought to have existed over 3 billion years ago were such that the spontaneous (inorganic) formation of organic macromolecules could have taken place..The interactions of these molecules would have increased as their concentrations increased. Reactions would have led tothe building of larger, more complex molecules. A pre-cellular life would have began with the formation of nucleic acids.Chemicals made by these nucleic acids would have remained in proximity to the nucleic acids. Eventually the pre-cellswould have been enclosed in a lipid-protein membrane, which would have resulted in the first cells.Biochemically, living systems are separated from other chemical systems by three things. 1. The capacity for replication from one generation to another. Most organisms today use DNA as the hereditary material, although recent evidence (ribosome) suggests that RNA may have been the first nucleic acid system to have formed. Nobel laureate Walter Gilbert refers to this as the RNA world. Recent studies suggest a molecular 2. The presence of enzymes and other complex molecules essential to the processes needed by living systems. Millers experiment showed how these could possibly form. 3. A membrane that separates the internal chemicals from the external chemical environment. This also delimits the cell from not-cell areas. The work of Sidney W. Fox has produced proteinoid spheres, which while not cells, suggest a possible route from chemical to cellular life. 27
  28. 28. Fossil evidence supports the origins of life on Earth earlier than 3.5 billion years ago. The North Pole microfossils fromAustralia, are complex enough that more primitive cells must have existed earlier. From rocks of the Ishua Super Group inGreenland come possibly the earliest cells, as much as 3.8 billion years old. The oldest known rocks on Earth are 3.96billion years old and are from Arctic Canada. Thus, life appears to have begun soon after the cooling of the Earth andformation of the atmosphere and oceans.Microfossils from the Apex Chert, North Pole, Australia. These organisms are Archean in age, approximately 3.465 billionyears old, and resemble filamentous cyanobacteria.These ancient fossils occur in marine rocks, such as limestones and sandstones, that formed in ancient oceans. Theorganisms living today that are most similar to ancient life forms are the archaebacteria. This group is today restricted tomarginal environments. Recent discoveries of bacteria at mid-ocean ridges add yet another possible origin for life: at thesemid-ocean ridges where heat and molten rock rise to the Earths surface.Archaea and Eubacteria are similar in size and shape. When we do recover "bacteria" as fossils those are the two featureswe will usually see: size and shape. How can we distinguish between the two groups: the use of molecular fossils that willpoint to either (but not both) groups. Such a chemical fossil has been found and its presence in the Ishua rocks ofGreenland (3.8 billion years old) suggests that the archeans were present at that time.Is there life on Mars, Venus, anywhere else??The proximity of the Earth to the sun, the make-up of the Earths crust (silicate mixtures, presence of water, etc.) and thesize of the Earth suggest we may be unique in our own solar system, at least. Mars is smaller, farther from the sun, has alower gravitational field (which would keep the atmosphere from escaping into space) and does show evidence of runningwater sometime in its past. If life did start on Mars, however, there appears to be no life (as we know it) today. Venus, thesecond planet, is closer to the sun, and appears similar to Earth in many respects. Carbon dioxide build-up has resulted ina "greenhouse planet" with strong storms and strongly acidic rain. Of all planets in the solar system, Venus is most likelyto have some form of carbon-based life. The outer planets are as yet too poorly understood, although it seems unlikely thatJupiter or Saturn harbor life as we know it. Like Goldilocks would say "Venus is too hot, Mars is too cold, the Earth isjust right!" 28
  29. 29. Mars: In August 1996, evidence of life on Mars (or at least the chemistry of life), was announced.. The results of years ofstudy are inconclusive at best. The purported bacteria are much smaller than any known bacteria on Earth, were nothollow, and most could possibly have been mineral in origin. However, many scientists consider that the chemistry of lifeappears to have been established on Mars. Search for martian life (or its remains) continues.Terms applied to cellsHeterotroph (other-feeder): an organism that obtains its energy from another organism. Animals, fungi, bacteria, and mantprotistans are heterotrophs.Autotroph (self-feeder): an organism that makes its own food, it converts energy from an inorganic source in one of twoways. Photosynthesis is the conversion of sunlight energy into C-C covalent bonds of a carbohydrate, the process bywhich the vast majority of autotrophs obtain their energy. Chemosynthesis is the capture of energy released by certaininorganic chemical reactions. This is common in certain groups of likely that chemosynthesis predates photosynthesis. Atmid-ocean ridges, scientists have discovered black smokers, vents that release chemicals into the water. These chemicalreactions could have powered early ecosystems prior to the development of an ozone layer that would have permitted lifeto occupy the shallower parts of the ocean. Evidence of the antiquity of photosynthesis includes: a) biochemicalprecursors to photosynthesis chemicals have been synthesized in experiments; and b) when placed in light, thesechemicals undergo chemical reactions similar to some that occur in primitive photosynthetic bacteria.Prokaryotes are among the most primitive forms of life on Earth. Remember that primitive does not necessarily equate tooutdated and unworkable in an evolutionary sense, since primitive bacteria seem little changed, and thus may be viewedas well adapted, for over 3.5 Ga. Prokaryote (pro=before, karyo=nucleus): these organisms lack membrane-boundorganelles. Some internal membrane organization is observable in a few prokaryotic autotrophs, such as thephotosynthetic membranes associated with the photosynthetic chemicals in the photosynthetic bacterium Prochloron..The Cell Theory is one of the foundations of modern biology. Its major tenets are: • All living things are composed of one or more cells; • The chemical reactions of living cells take place within cells; • All cells originate from pre-existing cells; and • Cells contain hereditary information, which is passed from one generation to another. 29
  30. 30. Components of CellsCell Membrane (also known as plasma membrane or plasmalemma) is surrounds all cells. It: 1) separates the inner partsof the cell from the outer environment; and 2) acts as a selectively permeable barrier to allow certain chemicals, namelywater, to pass and others to not pass. In multicellular organisms certain chemicals on the membrane surface act in therecognition of self. Antigens are substances located on the outside of cells, viruses and in some cases other chemicals.Antibodies are chemicals (Y-shaped) produced by an animal in response to a specific antigen. This is the basis ofimmunity and vaccination.Hereditary material (both DNA and RNA) is needed for a cell to be able to replicate and/or reproduce. Most organismsuse DNA. Viruses and viroids sometimes employ RNA as their hereditary material. Retroviruses include HIV (HumanImmunodefficiency Virus, the causative agent of AIDS) and Feline Leukemia Virus (the only retrovirus for which asuccessful vaccine has been developed). Viroids are naked pieces of RNA that lack cytoplasm, membranes, etc. They areparasites of some plants and also as possible glimpses of the functioning of pre-cellular life forms. Prokaryotic DNA isorganized as a circular chromosome contained in an area known as a nucleoid. Eukaryotic DNA is organized in linearstructures, the eukaryotic chromosomes, which are associations of DNA and histone proteins contained within a doublemembrane nuclear envelope, an area known as the cell nucleus.Organelles are formed bodies within the cytoplasm that perform certain functions. Some organelles are surrounded bymembranes, we call these membrane-bound organelles.Ribosomes are the tiny structures where proteins synthesis occurs. They are not membrane-bound and occur in all cells,although there are differences between the size of subunits in eukaryotic and prokaryotic ribosomes.The Cell Wall is a structure surrounding the plasma membrane. Prokaryote and eukaryote (if they have one) cell wallsdiffer in their structure and chemical composition. Plant cells have cellulose in their cell walls, other organisms havedifferent materials comprising their walls. Animals are distinct as a group in their lack of a cell wall.Membrane-bound organelles occur only in eukaryotic cells. They will be discussed in detail later. Eukaryotic cells aregenerally larger than prokaryotic cells. Internal complexity is usually greater in eukaryotes, with their compartmentalizedmembrane-bound organelles, than in prokaryotes. Some prokaryotes, such as Anabaena azollae, and Prochloron, haveinternal membranes associated with photosynthetic pigments.The Origins of MulticellularityThe oldest accepted prokaryote fossils date to 3.5 billion years; Eukaryotic fossils to between 750 million years andpossibly as old as 1.2-1.5 billion years. Multicellular fossils, purportedly of animals, have been recovered from 750Marocks in various parts of the world. The first eukaryotes were undoubtedly Protistans, a group that is thought to have givenrise to the other eukaryotic kingdoms. Multicellularity allows specialization of function, for example muscle fibers arespecialized for contraction, neuron cells for transmission of nerve messages.MicroscopesMicroscopes are important tools for studying cellular structures. In this class we will use light microscopes for ourlaboratory observations. Your text will also show light photomicrographs (pictures taken with a light microscope) andelectron micrographs (pictures taken with an electron microscope). There are many terms and concepts which will helpyou in maximizing your study of microscopy.There are many different types of microscopes used in studying biology. These include the light microscopes (dissecting,compound brightfield, and compound phase-contrast), electron microscopes (transmission and scanning), and atomicforce microscope. 30
  31. 31. The microscope is an important tool used by biologists to magnify small objects. There are several concepts fundamentalto microscopy.Magnification is the ratio of enlargement (or eduction) between the specimen and its image (either printed photograph orthe virtual image seen through the eyepiece). To calculate magnification we multiply the power of each lens throughwhich the light from the specimen passes, indicating that product as GGGX, where GGG is the product. For example: ifthe light passes through two,lenses (an objective lens and an ocular lens) we multiply the 10X ocular value by the value ofthe objective lens (say it is 4X): 10 X 4=40, or 40X magnification.Resolution is the ability to distinguish between two objects (or points). The closer the two objects are, the easier it is todistinguish recognize the distance between them. What microscopes do is to bring small objects "closer" to the observerby increasing the magnification of the sample. Since the sample is the same distance from the viewer, a "virtual image" isformed as the light (or electron beam) passes through the magnifying lenses. Objects such as a human hair appear smooth(and feel smooth) when viewed with the unaided or naked) eye. However, put a hair under a microscope and it takes on aVERY different look!Working distance is the distance between the specimen and the magnifying lens.Depth of field is a measure of the amount of a specimen that can be in focus.Magnification and resolution are terms used frequently in the study of cell biology, often without an accurate definition oftheir meanings. Magnification is a ratio of the enlargement (or reduction) of an image (drawing or photomicrograph),usually expressed as X1, X1/2, X430, X1000, etc. Resolution is the ability to distinguish between two points. Generallyresolution increases with magnification, although there does come a point of diminishing returns where you increasemagnification beyond added resolution gain.Scientists employ the metric system to measure the size and volume of specimens. The basic unit of length is the meter(slightly over 1 yard). Prefixes are added to the "meter" to indicate multiple meters (kilometer) or fractional meters(millimeter). Below are the values of some of the prefixes used in the metric system. kilo = one thousand of the basic unit meter = basic unit of length centi = one hundreth (1/100) of the basic unit milli = one thousandth (1/1000) of the basic unit micro = one millionth (1/1,000,000) of the basic unit nano = one billionth (1/1,000,000,000) of the basic unitThe basic unit of length is the meter (m), and of volume it is the liter (l). The gram (g). Prefixes listed above can beapplied to all of these basic units, abbreviated as km, kg, ml, mg, nm....etc. The Greek letter micron (µ) is applied to smallmeasurements (thousandths of a millimeter), producing the micrometer (symbolized as µm). Measurements in microscopyare usually expressed in the metric system. General units you will encounter in your continuing biology careers includemicrometer (µm, 10-6m), nanometer (nm, 10-9m), and angstrom (Å, 10-10m).Light microscopes were the first to be developed, and still the most commonly used ones. The best resolution of lightmicroscopes (LM) is 0.2 µm. Magnification of LMs is generally limited by the properties of the glass used to makemicroscope lenses and the physical properties of their light sources. The generally accepted maximum magnifications inbiological uses are between 1000X and 1250X. Calculation of LM magnification is done by multiplying objective valueby eyepiece value.The compound light microscope, uses two ground glass lenses to form the image. The lenses in this microscope, however,are aligned with the light source and specimen so that the light passes through the specimen, rather than reflects off thesurface. The compound microscope provides greater magnification (and resolution), but only thin specimens (or thinslices of a specimen) can be viewed with this type of microscope. 31

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