Cell Biology

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Cell Biology

4.1 Elements, Compounds, and ReactionsIn the 1950s, American scientist Stanley Miller tried to find a recipe for life. He putchemicals found in Earth’s early atmosphere into a closed container. Then he sent anelectric charge through that mixture to simulate lightning going through theatmosphere (Figure 4.1). When he analyzed the container after a few days, he foundamino acids. Amino acids are the building blocks of proteins—one of the compoundsthat make up all living things. But he did not find a recipe for making life.Scientists know the basic ingredients for life. They just don’t know the recipe. In thissection, you’ll learn about the simplest ingredients that make up living things.The ingredients for lifeLife is a form ofchemistryElements in livingthingsLiving thingshave complexmoleculesYou have learned that all living things are made of cells. A cell isthe basic unit of life. Where did the first cells come from? How didthings go from nonliving to living? Scientists really don’t know theanswers to these questions. We do know that life is a form ofchemistry. So learning some chemistry is a good place to start.The ingredients for life are simple. Your body is made mostly ofthree elements: carbon, oxygen, and hydrogen. An element is thesimplest form of matter. Your body also contains sulfur, nitrogen,phosphorus, and about a dozen other elements. These are found inyour body in smaller amounts than carbon, hydrogen, and oxygen.Every living thing is made from these ingredients (Figure 4.2).Like you, the atmosphere is also made mostly of carbon, hydrogen,and oxygen. But the atmosphere is not alive. The key to life is howthese elements are put together. In the atmosphere, they are inthe form of simple compounds like carbon dioxide and water. Inliving things, elements are found in very complex molecules thatwork together in cells. There are also simple compounds, likewater, in living systems.Figure 4.1: Stanley Miller’sexperiment.Figure 4.2: The elements that makeup living things (percent by mass).element - the simplest form ofmatter.70UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONSAtoms, compounds, and moleculesAtomsCompoundsMoleculesA single atom is the smallest particle of an element that keeps thechemical identity of the element. Each element has a unique typeof atom. Carbon atoms are different from hydrogen atoms, andhydrogen atoms are different from oxygen atoms. All atoms of agiven element are similar to each other. If you examined a millionatoms of carbon you would find them all to be similar.Sometimes elements are found in their pure form, but more oftenthey are combined with other elements. Most substances containseveral elements combined together. A compound is a substancethat contains two or more different elements that are chemicallyjoined. For example, water is a compound that is made from theelements hydrogen and oxygen.If you could magnify a sample of pure water so you could see itsatoms, you would notice that the hydrogen and oxygen atoms arejoined together in groups of two hydrogen atoms to one oxygenatom. These groups are called molecules. A molecule is a group oftwo or more atoms joined together chemically. Many substancesyou encounter are a mixture of different elements and compounds.Air is an example of a mixture that contains nitrogen, oxygen,water vapor, carbon dioxide, argon, and other gases. The elementsand compounds in a mixture are not chemically joined together.Figure 4.3: Compounds.atom - the smallest particle of anelement that keeps the chemicalidentity of that element.compound - a substance thatcontains two or more differentelements that are chemicallyjoined.molecule - a group of two ormore atoms joined togetherchemically.4.1 ELEMENTS, COMPOUNDS, AND REACTIONS71


Chemical reactionsWhat arechemicalreactions?A simplechemical reactionAll of the millions and millions of different compounds are made ofonly 92 elements combined in different ways. Just as you can spellthousands of words with the same 26 letters, you can make all ofchemicals in the world from just 92 elements. How are all of thesedifferent compounds made? The answer is chemical reactions. Achemical reaction is a process that rearranges the atoms of one ormore substances into one or more new substances.Hydrogen reacts with oxygen to produce water and energy. Howdo we show this chemical reaction? In cooking you start withingredients that are combined to make different foods. In chemicalreactions you start with reactants that are combined to makeproducts. The reactants and products may include atoms,molecules, and energy. Two hydrogen molecules combine with oneoxygen molecule to make two water molecules. Hydrogen andoxygen are the reactants. Water and energy are the products.chemical reaction - a processthat rearranges the atoms of oneor more substances into one ormore new substances.Life useschemicalreactionsCells use many chemical reactions. You might say that life is aseries of chemical reactions (Figure 4.4). Your cells constantlyrearrange molecules to make energy for movement, thinking, andeven sleeping. Plant cells use a chemical reaction to store energyfrom the sun in the form of molecules.Figure 4.4: Life is a series ofchemical reactions.72UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONSThe importance of waterWhy is waterimportant?Why watersupports lifeWhen scientists search for life in other parts of our solar system,they begin by looking for water. Why? Water (in its liquid state) isessential to life as we know it. Your body is about 60% water. Thereactions that sustain life need liquid water to work. Liquid wateris also used to transport molecules where they need to go, insideand outside of cells.Water has many properties that help sustain life. Three of the mostimportant properties are:1. Water is a good solvent. A solvent is a substance that iscapable of dissolving another substance. Water dissolves justabout anything. In fact, it’s such a good solvent that waterrarely exists as pure water. When water has one or moresubstances dissolved in it, we call it a solution (Figure 4.5).Even the water that comes out of your faucet is a solution. Allof the water in your body has dissolved substances in it. Manyreactions in living systems occur in solutions.2. Water exists as a liquid at a large range of temperatures.Pure water freezes at 0°C (32°F) and boils at 100°C (212°F).Add salt and you can lower the freezing temperature. Somesalty solutions have freezing points below –10°C. Increase thepressure and the boiling temperature is raised. Deep-sea ventwaters can reach over 340°C before boiling (Figure 4.6).3. Water has a high specific heat. Specific heat is the amountof heat needed to raise one mL of water by 1°C. Water has oneof the highest specific heats of any substance known. Thismeans that it takes a lot of energy to raise the temperatureof water even a few degrees. This high specific heat helpsstabilize the temperatures in living systems.Figure 4.5: Solutions in livingsystems.Figure 4.6: The boiling temperatureof water in deep-sea vents can reach over340°C.4.1 ELEMENTS, COMPOUNDS, AND REACTIONS73


4.1 Section Review1. What are the three main elements that make up living things?2. Which statement best describes the molecules found in livingsystems?a. They contain mostly sulfur, gold, and lead.b. They are very simple molecules made of carbon andhydrogen.c. They are very complex molecules made mostly of carbon,hydrogen, and oxygen.3. Classify each example below as an element or a compound.4. Many homes are heated with a compound called methane, ornatural gas. Methane reacts with oxygen to produce carbondioxide and water.a. What are the reactants in this reaction?b. What are the products in this reaction?5. List the three properties of water that make it a good supporterof life.6. Give an example of a solution found inside of a living system.How much water do you use?You could not live without a supplyof freshwater. You drink waterwhen you’re thirsty because everycell in your body needs it. You alsouse water every day for otherthings besides drinking. Do youknow how much water you useeach day? Find out by followingthe steps below. Record yourfindings in your journal.1. From the moment you wake upon a typical school day, keeptrack of all of your activities thatuse water.2. Estimate how much water (ingallons) each activity uses. Onaverage, a faucet uses aboutone gallon per minute. Watersavingtoilets use about 1.5gallons of water per flush.Older toilets use about 5gallons of water per flush.3. Add up the total amount ofwater you use in a day.Compare your amount toothers in your class.4. Make a list of ways you canconserve water. For example,you could turn off the faucetwhile brushing your teeth.74UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONS4.2 Carbon Compounds and CellsSo now you know the basic ingredients found in living things. But how are theseingredients put together? Most molecules that make up living things are very largeand complex. In this section, you will learn about their structure and function.Carbon compoundsLife is carbonbasedYou use carboncompoundsevery dayCarboncompounds inliving thingsLife as we know it is carbon based. This means that most of thecompounds you are made of contain the element carbon. Carbonis unique among the elements. A carbon atom can form chemicalbonds with other carbon atoms in long chains or rings (Figure 4.7).Some carbon compounds contain several thousand carbon atoms.Carbon compounds are not only found in living things. You usecarbon compounds every day. Plastic, rubber, and gasoline arecarbon compounds. In fact, there are over 12 million known carboncompounds!The carbon compounds in living things areclassified into four groups: carbohydrates,lipids, proteins, and nucleic acids.Figure 4.7: A carbon chain and acarbon ring.4.2 CARBON COMPOUNDS AND CELLS75


Carbohydrates, fats, and proteinsFoods containthe compoundsyou are made ofWhat is acarbohydrate?Sugars aresimple moleculesStarches arelarger moleculesThe compounds that your cells are made of and that they use tofunction come from the foods you eat. Foods containcarbohydrates, fats (also known as lipids), and proteins. Theamount of each varies with different foods. What arecarbohydrates, fats, and proteins?Carbohydrates are energy-rich compounds made from carbon,hydrogen, and oxygen. Cells use carbohydrates to get and storeenergy. Plants contain cellulose, a carbohydrate that gives thema rigid structure.Carbohydrates are classified as sugars and starches. Sugarsare smaller molecules. Glucose is a simple sugar made of 6 carbon,12 hydrogen, and 6 oxygen atoms. The sugar you use to sweetenfood is called sucrose. A sucrose molecule is made from two glucosemolecules.Starch molecules are very large. They consist of many sugarmolecules combined. Plant cells store energy as starch. Many foodsthat contain starch come from plants. These include rice, potatoes,corn, and wheat.Figure 4.8: A glucose moleculecarbohydrates - energy-richcompounds such as sugars andstarches made from carbon,hydrogen, and oxygen.(discussed on next page)lipids - energy-rich compoundssuch as fats, oils, and waxes madefrom carbon, hydrogen, andoxygen.proteins - complex moleculesmade from smaller moleculescalled amino acids.76UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONSLipidsCholesterol is alipidProteinsEnzymes areproteinsProteins aremade of aminoacidsLike carbohydrates, lipids are energy-rich compounds made fromcarbon, hydrogen, and oxygen (Figure 4.9). Lipids include fats,oils, and waxes. Lipids are made by cells to store energy for longperiods of time. Animals that hibernate (sleep through the winter)live off of the fat stored in their cells. Polar bears have a layer of fatbeneath their skin to insulate them from very cold temperatures.Can you name some foods that contain lipids?Like fat, cholesterol is listed on food labels. Cholesterol is a lipidthat makes up part of the outer membrane of your cells. Your livernormally produces enough cholesterol for your cells to use. Toomuch cholesterol in some people’s diet may cause fat deposits ontheir blood vessels. This may lead to coronary artery disease. Foodsthat come from animals are often high in cholesterol.Proteins are very large molecules made of carbon, hydrogen,oxygen, nitrogen, and sometimes sulfur. Many animal parts likehair, fingernails, muscle, and skin, contain proteins. Hemoglobin isa protein in your blood that carries oxygen to your cells. Foods highin protein include meats, dairy products, and beans.An enzyme is a type of protein that cells use to speed up chemicalreactions. Digestive enzymes are made by the pancreas. Theseenzymes help break down the foods you eat into smaller moleculesthat can be absorbed by your cells.Protein molecules are made of smaller molecules calledamino acids. Your cells combine different amino acids in variousways to make different proteins. There are 20 amino acids used bycells to make proteins. You can compare amino acids to letters inthe alphabet. Just as you can spell thousands of words with just 26letters, you can make thousands of different proteins from just 20amino acids (Figure 4.10).Figure 4.9: A lipid molecule.Figure 4.10: Proteins are made fromsmaller molecules called amino acids.4.2 CARBON COMPOUNDS AND CELLS77


Nucleic acidsWhat are nucleicacids?DNANucleic acids are compounds made of long, repeating chainscalled nucleotides. Nucleotides are made from carbon, hydrogen,oxygen, nitrogen, and phosphorus. Each nucleotide contains asugar molecule, a phosphate molecule, and a base molecule. DNAis a nucleic acid that contains the information cells need to makeall of their proteins.A DNA molecule can becompared to a book thatcontains “recipes” formaking all of the proteinsthat you are made of. Somescientists refer to DNA asthe “blueprints” for life.You’ll learn more aboutDNA in Chapter 10.Nutrition and snack foods1. List your three favorite snackfoods.2. Collect a nutrition label fromeach food.3. If any of the foods on your listdon’t come in a package, youcan look up the nutritioninformation on the Internet.4. Write a paragraph about eachfood. Is it a good source ofcarbohydrates, lipids, andprotein? Would you considerthis food healthy? Why orwhy not?nucleic acids - molecules thatcontain information needed formaking proteins.78UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONS4.2 Section Review1. Explain why life is often referred to as “carbon-based.”2. What are the four groups of carbon compounds found in livingthings?3. You may have heard the saying, “You are what you eat.” Useinformation learned in this section to explain what thisstatement means.4. Classify each substance as either sugar, starch, protein, ornucleic acid.a. the major compound that makes up the skinb. glucosec. the major compound in potatoesd. DNA5. Complete the table below.CarboncompoundCarbohydrateLipidProteinNucleic acidElements that itis made fromFunction incellsExampleCounting CaloriesA food calorie tells you how muchenergy is in different foods. Eachtype of carbon compound has acertain number of food calories pergram. Fat contains 9 food caloriesper gram. Carbohydrate andprotein each contain 4 foodcalories per gram. Based on thisinformation, solve the following:1. How many food calories in theproduct above come from fat?2. How many food calories comefrom carbohydrate?3. How many food calories comefrom protein?4. How many food calories are ina serving of the product?4.2 CARBON COMPOUNDS AND CELLS79


4.3 Light and Living ThingsAn important tool for studying life is the microscope. The microscope magnifiesobjects so you can see their very small features. For instance, if you look at a tinybrine shrimp in a tank of water, you can barely make out its features. When you putone under a microscope, you’ll be amazed at what you can see (Figure 4.11). In thissection, you will learn about the properties of light and how a microscope works.Light is very important to life and you’ll learn more about it in other chapters.The behavior of lightWhat is light?Light travels instraight linesWhat happenswhen light hits adifferentmaterial?AbsorptionLight is a form of energy—like heat and sound. It travels very fastand over long distances. Light travels at the amazing speed of299,792,458 (approximately 300,000,000) meters per second! Thisis called the speed of light.Light given off from objects like a light bulb or the Sun travels instraight lines. We can show how light travels using imaginarylines called light rays. Each light ray represents a thin beam oflight and is drawn with an arrow head that shows the direction oftravel. A diagram of the light rays coming from a light bulb or theSun is shown in Figure 4.12.Light travels in straight lines through a material (like air) until ithits a different material. Then, it can be absorbed, reflected, ortransmitted (which means “passed through”). Usually, all threethings happen.When light is absorbed, its energy is transferred to the absorbingmaterial. Black objects absorb almost all of the light that falls onthem. That is why a black road surface gets hot on a sunny day.Light energy from the Sun is absorbed by the road.Figure 4.11: A brine shrimp under amicroscope at 100X magnification.Figure 4.12: Light emitted from the Sunor from a light bulb travels in straight linesfrom the surface.microscope - magnifies objectsso you can see their features.light ray - an imaginary line thatrepresents a thin beam of light.80UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONSReflectionWhat isreflection?The angle ofincidence equalsthe angle ofreflectionRegular andscatteredreflectionReflection occurs when light bounces off of a surface. Imagine a rayof light striking a mirror. The incident ray is the light ray thatstrikes the surface of the mirror. The reflected ray is the light raythat bounces off the surface of the mirror (Figure 4.13, top).The lower part of Figure 4.13 shows the reflection of a light ray.The angle of incidence is the angle between the incident ray and animaginary line drawn perpendicular to the surface of the mirrorcalled the normal line. Perpendicular means “at a 90 degree angle,”also called a right angle. The angle of reflection is the anglebetween the reflected light ray and the normal line. The angle ofincidence is always equal to the angle of reflection.When you look in a mirror, you can see your image because whenparallel light rays hit the mirror at the same angle, they are allreflected at the same angle. This is called regular reflection. Youcan’t see your image when you look at a white piece of paperbecause even though it seems smooth, its surface has tiny bumpson it. When parallel light rays hit a bumpy surface, the bumpsreflect the light rays at different angles. Light rays reflected atdifferent angles cause scattered reflection. Many surfaces, forexample, polished wood, are in between rough and smooth andcreate both types of reflection.reflection - occurs when lightbounces off a surface.incident ray - the light ray thatstrikes a surface.reflected ray - the light ray thatbounces off a surface.Figure 4.13: The angle of incidenceis always equal to the angle of reflection.4.3 LIGHT AND LIVING THINGS81


RefractionRefraction is thebending of lightTransparent materials like air, glass and water allow lightto be transmitted. Refraction is the bending of light as it crossesa boundary between two different transparent materials. Almostevery time light passes from one type of matter into another, itwill change speed. For example, light travels slightly faster in airthan in water. When a light ray traveling through air enters glassit slows down and refracts, bending toward the normal line. Thisbending effect takes place whenever light slows as it moves fromone material into another. The opposite effect happens when lightspeeds up as it moves from one material into another. Forexample, when light goes from glass to air, it speeds up, bendingaway from the normal line.AirGlassAirFigure 4.14: Refraction is thebending of light as it crosses a boundarybetween two different materials.Refractionchanges howobjects lookA glass rod in water is a good example of refraction (Figure 4.15).The glass rod appears to break where it crosses the surface of thewater, but this is just an illusion. The illusion is caused byrefracted light rays. The light rays from the glass rod are refracted(or bent) when they cross from water, into glass, and back into airbefore reaching your eyes. Do you think the illusion would stillhappen if there were no water in the glass? Try it and see.Figure 4.15: This illusion is createdbecause light is refracted as it travelsfrom air to water.refraction - the bending of lightas it crosses a boundary betweentwo different transparent materials.82UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONSLensesA lens and itsoptical axisConvex lensesA lens is an object that is designed to refract light in a specific way.Many devices you use contain lenses (Figure 4.16). All lenses havean imaginary line that goes through the center called an axis.While there are different kinds of lenses, light traveling along theaxis of any lens is not bent. There are two basic kinds of lenses;convex and concave.Light rays that enter a convex lens parallel to its axis refract andmeet at a point called the focal point. The distance from the centerof the lens to the focal point is the focal length. Convex lenses aresometimes called converging lenses.lens - an object designed torefract light in a specific way.focal point - a point where lightrays meet.focal length - the distance fromthe center of the lens to the focalpoint.Concave lensesLight rays that enter a concave lens parallel to its axis refract andspread out, diverging (moving apart from each other) as they exitthe lens. The focal point of a concave lens is located on the sameside of the lens as the light source. Imaginary lines are drawnbackward in the opposite direction of the diverging rays. The focalpoint is where the imaginary lines meet. The distance from thefocal point to the center of the lens is its focal length. Concavelenses are sometimes called diverging lenses.Figure 4.16: Some devices that uselenses.4.3 LIGHT AND LIVING THINGS83


How a microscope worksMicroscopeshave an objectivelens and aneyepieceFocusing theimageMagnificationMost microscopes use at least two lenses. The lens closest to theobject to be viewed is called the objective. It has a very short focallength and creates a larger, inverted image of the object inside themicroscope. Inverted means that the image appears upside downor backward compared with theactual object. The lens you lookthrough is called the eyepiece andhas a longer focal length. Theimage from the objective lens iscloser than one focal length tothe eyepiece. That means theeyepiece acts like a magnifyingglass, magnifying the (alreadylarger) image from the objective.A microscope has a stage wherethe object to be viewed is placed.The stage can be moved up ordown to focus the image. Mostmicroscopes also have a lightsource to illuminate the object tobe viewed or shine light througha semitransparent object on aslide.Each lens on a microscope has a magnification value. The totalmagnification of the image is the power of the objective lensmultiplied by the power of the eyepiece. For example, a 10×eyepiece lens with a 6× objective lens produces an overallmagnification of 60× (10 × 6). Figure 4.17 shows an image at 40×,100×, and 400× total magnification.Figure 4.17: A brine shrimpmagnified 40× and 100×. and 400x.Which magnification is best when youwant to see the entire organism?84UNIT 2 CELL BIOLOGY


CHAPTER 4: CHEMISTRY AND PHYSICS CONNECTIONS4.3 Section Review1. Name three things that can happen when light moves from onematerial, like air, to another, like water.2. The picture below shows a light ray striking a mirror andbouncing off. Use the picture to answer the questions below.A ray of light strikes a mirror.Which of the following rays (a, b, c,or d) best describes the path of thelight ray leaving the mirror?a. What is A called?b. What is B called?c. What is C called?d. If A measures 30 degrees, what is the measurement of C?3. Why does light refract when it crosses from air to glass?4. Calculate the total magnification for each combination of lenseson a microscope:a. objective lens: 10× eyepiece: 10×b. objective lens: 2× eyepiece: 5×5. Explain how reflection and refraction are involved in how amicroscope works.4.3 LIGHT AND LIVING THINGS85


Chapter 4 ConnectionYou may wear glasses to helpyou see the chalkboard or to reada book. Sherlock Holmes had hismagnifying glass to solvemysteries and to search for clues.Scientists also have their ownspecial looking glass for seeingand discovering-the microscope!Modern day science wouldn't bethe same without it. How elsewould we know about bacteria,viruses, and cells of the humanbody?A brief history of themicroscopeMicroscopes are instrumentsused to magnify objects too smallto be seen with the naked eye.The Janssen family of Hollandinvented the first microscope in1595. This simple instrumentwas made of glass lenses likethose used to make eyeglasses.In the 17th century, amateurscientist Anton vanLeeuwenhoek created amicroscope in which tinyorganisms could be seen. He usedGlow Cell Glow!150016001700180019002000his invention to study pond water and referred to smallcreatures he saw as “animalcules.”MicroscopeTimeline1595 - Janssen invented the firstmicroscope made of crude glass.1675 - Anton van Leeuwenhoek created amicroscope in which he saw "animacules".In the 18th century, microscopes became more widely usedas there quality increased. Microscopes continued to improve18th century - Microscopes lenses madeby combining two different glasses, giving aclearer image19th and 20th centuries -Microscopes continued to improve magnificationand clarityEarly 20th century - fluorescentmicroscopy developed by August Kohler, CarlReichert, and Heinrich Lehmann. Decades later itwas perfected and more widely used.1932 - Frits Zernike invents the phase contrastmicroscope, which allows colorless objects to be seen.1938 - Ernst Ruska invents the electronmicroscope , which make it possible to see objectsas small as the diameter of an atom.1981 - Gerd Bennig and Heinrich Rohrer inventthe scanning tunneling microscope, which give 3-Dimages of objects at the atomic level.magnification and clarity during the 19thand 20th centuries.In 1932, the phase contrast microscopeallowed scientists to study colorlessmaterials. In 1938, the electron microscopemade it possible to see objects that couldnever been seen before. In fact, it allowedscientists to see materials as small as thediameter of an atom! Finally, the scanningtunneling microscope was invented in1981. This powerful instrument gavescientists three-dimensional images ofincredibly small objects.Rainbows and wavelengthsAll observations made under themicroscope depend on what we see with oureyes. It is important to understand how wesee color. The colors of the spectrum (or therainbow) that are visible to the human eyeeach have a unique wavelength. The visiblecolors from shortest to longest wavelengthare violet, blue, green, yellow, orange, andred. Our eyes cannot detect light that fallsoutside of this visible rainbow. Forexample, ultraviolet (UV) light has ashorter wavelength than the violet we seeon the rainbow. Infrared light has alonger wavelength than the red we see onthe rainbow.THE ELECTROMAGNETIC SPECTRUMRadiowavesVisible lightMicrowaves Infrared Ultraviolet X-raysLonger wavelengthShorter wavelength86


The fluorescence phenomenonIn the mid 1800s, the British scientist Sir George G. Stokesdiscovered a mineral called fluorspar. This mineral glowedwhen lit with ultraviolet light. The fluorspar absorbed theUV light and produced a glowinglight that is visible to the humaneye. Stokes referred to thisphenomenon as “fluorescence.”Development of fluorescentmicroscopeScientists in the early twentiethcentury worked on thedevelopment of the firstfluorescent microscope. It wouldtake decades until it becameperfected and more widely used.Today, the use of fluorescencemicroscopes is an important toolin cellular biology. Scientists useit to find out about cellstructures, molecules, andproteins. They are able to study the function of cells andtheir parts.Cells usually do not glow. Researchers use variousfluorescent proteins known as probes to make cells glow.They have developed probes that are green, blue, yellow,orange, and red. The cells absorb these probes like dyes.The fluorescent microscope uses filters that only let in lightof wavelengths matching the fluorescing material beingstudied. All other wavelengths are blocked out. Thefluorescing areas shine out against a dark background,making cells and their structures glow.Research with fluorescenceThere are countless ways the fluorescent microscope is usedin scientific research. An example is Dr. Thomas Hoock, whohas been working in the cellular biology field for 20 years. Hehas worked in a variety ofsettings, and much of hiswork has involved the use ofthe fluorescent microscope.Dr. Hoock used fluorescentmicroscopy early in hiscareer to study disordersrelated to high bloodpressure. Using this tool, heexplored how cells of thecardiovascular system move.Dr. Hoock also used thefluorescent microscope tostudy the behavior of cellsthat make up our immunesystem. Today, Dr. Hoock isa senior staff investigator ofVertex Pharmaceuticals inCambridge, Massachusetts. At Vertex, he and his fellowscientists use fluorescence microscopy's to study newmedicines. He explains that he enjoys his work as a scientistbecause he must be a creative thinker and that each day isnever the same.Questions:1. How has the development of the microscope progressedover the past several hundred years?2. How are wavelengths related to how we see color?3. How was fluorescence first discovered?4. How is the fluorescent microscope used in cellular biology?Chapter 4 ConnectionUNIT 2 CELL BIOLOGY87


Chapter 4 ActivityScientists have learned over theyears that what you eat can affectyour health. Food packages arerequired by law to have NutritionFacts labels. In this activity, youwill study some breakfast cerealNutrition Facts labels. Maybe youwill learn some new things aboutyour favorite cereal!Cereal Nutrition FactsHow to read a Nutrition Facts label1. Each group should have one box of cereal. The first pieceof information on the Nutrition Facts label is serving size.This is very important, because all of the nutritioncontent information is based on this serving size.Measure out one serving of the cereal and pour it into asmall bowl. Is this the amount that you would usuallyeat?2. Find the number of Calories in one serving of the cereal.Calories measure how much energy you get from the foodyou eat. The major nutrients present in the foods we eatare called fats, carbohydrates, and proteins, and each ofthese nutrients contributes to the number of totalCalories. Why do you suppose Calories from fat is listednext to the number of Calories, but not Calories fromcarbohydrates or protein?3. Nutrients listed on the label can be divided into threecategories: nutrients you should limit, nutrients that mayor may not be an issue, and nutrients you should be sureto include enough of in your diet. The nutrients youshould limit are fat, cholesterol, and sodium. What do youknow about health problems related to high intakes ofthese nutrients? Carbohydrates and protein are nutrientsthat most Americans eat plenty of, but some may want tolimit sugars. Dietary fiber, vitamin A, calcium, vitaminC, and iron are all nutrients that we should be sure to getenough of in our diet. Why are these important?4. The % daily value numbers provide a quick, helpfulguideline for you to follow when you are trying to limit oreat more of certain nutrients. The percentages are basedon an average daily intake of 2000 Calories. Look at yourcereal label. Are there any % daily value numbers thatsurprise you?5. Design a data table that will allow you to organize thefollowing information about each of 6 different breakfastcereals: cereal name, serving size, total Calories, Caloriesfrom fat, total fat (g), saturated fat (g), cholesterol (mg),sodium (mg), total carbohydrate (g), dietary fiber (g),sugars (g), protein (g), vitamin A (%), calcium (%),vitamin C (%), iron (%).6. Record the nutrition data from your cereal box, and thentrade with other groups until you have recorded datafrom each box of cereal. Use the data you collected toanswer the questions.Applying your knowledgea. Determine which cereal is the healthiest. Explain howyou arrived at your answer, and refer to specific datafrom your comparison table.b. Determine which cereal is the least healthy, and use datato justify your choice.c. Compare your choices with others in your group. Dideveryone agree?d. Why are Nutrition Facts labels so important that thegovernment requires them?e. Write one question that you still have about NutritionFacts labels.88


Chapter 4 AssessmentVocabularySelect the correct term to complete the sentences.atomcarbohydrates chemical reactioncompoundelementlipidsmoleculereflectionfocal pointrefractionnucleic acids proteinslensSection 4.11. Propane and water are both examples of ____s.2. Plants use a ____ to store energy from the sun in the form ofmolecules.3. A(n) ____ is the smallest particle of an element that keepsthe chemical identity of that element.4. All the different compounds in the world are made up of only92 different ____s.Section 4.25. Sugars and starches are two types of ____, energycompounds made from carbon.6. ____ are made from amino acids.7. Cells use ____, such as waxes, oils, and fats, to store energyfor long periods of time.8. ____ contain the information needed to make proteins.Section 4.39. ____ happens when light passes from air into water.10. ____ happens when light bounces off a surface.11. A ____ is designed to refract light in a certain way.12. The ____ of a lens is where converging light rays meet.ConceptsSection 4.11. Why do you think oxygen and hydrogen are two of the mostabundant elements found in living things? Explain youranswer.2. Explain the relationship between atoms, elements,compounds, and mixtures.3. The chemical reaction for respiration is:C 6 H 12 O 6 (Glucose) + 6O 2 (Oxygen) →6CO 2 (Carbon dioxide) + 6H 2 O (Water) + Energy (ATP)Identify the following in the equation:a. reactantsb. productsc. elementsd. compoundsSection 4.24. Identify each of the following as a carbohydrate, lipid,protein, or nucleic acid.a. glucoseb. hemoglobinc. DNAd. digestive enzymese. cholesterolf. cellulose5. An organic compound contains carbon, hydrogen, oxygen,and nitrogen. Could this compound be a lipid? Could it be anucleic acid? Explain.6. Which two organic compounds serve as energy sources? Howdo these two groups differ?7. How are proteins and nucleic acids related?CHAPTER 4 CHEMISTRY AND PHYSICS CONNECTIONS89


Section 4.38. When light hits a material, what are three things that canhappen?9. Explain the differences between a converging lens and adiverging lens. For each lens: discuss the shape, how eachbends parallel light rays, and how the images are formed.Math and Writing SkillsSection 4.11. Create a pie graph to represent the elements found in livingthings. Use the data found in Figure 4.2.2. The chemical reaction for respiration is:C 6 H 12 O 6 (Glucose) + 6O 2 (Oxygen) → 6CO 2 (Carbondioxide) + 6H 2 O (Water) + Energy (ATP)a. How many molecules of oxygen are needed to breakdown each molecule of glucose?b. In the reactants, how many atoms of oxygen are there?Atoms of carbon? Atoms of hydrogen?c. In the products, how many atoms of oxygen are there?Atoms of carbon? Atoms of hydrogen?Section 4.23. Suppose that there are only three amino acids that arecalled 1, 2, and 3. If all three are needed to make a protein,how many different proteins could be made? Each aminoacid may only appear in each protein once. Also, the positionof the amino acid is important - 123 is not the same as 321.Show your number arrangements to support your answer.4. You are entering a contest to design a new advertisingcampaign for National Nutrition Awareness Week. Create aslogan and written advertisement that encourages teens toeat the right amounts of carbohydrates, lipids, or proteins.Use at least three facts to make your advertisementconvincing.Section 4.35. A light ray strikes a mirror at an angle of 35 degrees. Atwhat angle does the light ray reflect off the mirror?Chapter ProjectCreate a nutrition card gameFind 6 - 10 nutrition facts labels. Cut them from food packagesor print them out from the website www.nutritiondata.com. Tryto make the labels about the size of a regular playing card. Pastethe labels onto cardboard. Make sure the serving size shows onthe label, but no information that could give away the identity ofthe type of food. Place a number in one corner of the label so youcan identify the label later. Choose many different types of foods.Make 6 - 10 identical cards pasted onto the same type of backing.On these cards, carefully print the name of each food that youhave found nutrition facts labels for. Place a letter in one cornerof each name card. Make an answer key for yourself that showswhich nutrition facts label number goes with each food nameletter. That way, as your classmates compete to make matches,you can determine if the matches are correct.To play the game, shuffle the cards and place them face down ona table in several rows. On each turn, a player will turn over twocards and determine if a match is made. If they think they havea match, you must verify by looking at your answer key. If thematch is correct, the player takes the cards and takes anotherturn. If the match is incorrect, or if two of the same type of cardis chosen, the player's turn ends. Once all matches have beenmade, players count up the number of cards they have won andthe player with the most cards wins!90CHAPTER 4 CHEMISTRY AND PHYSICS CONNECTIONS


Chapter 5Cell Structure and FunctionCan you name something that you know exists even though you can’tsee it with your eyes? A drop of pond water has tiny swimmingorganisms and small bits of plant material, but we can’t always seethem with our eyes. How do we know there are tiny things in a dropof pond water? We can use a microscope to view the pond water.There are instruments people use every day to help them see thingsthey wouldn’t usually be able to see. Have you ever used a pair ofbinoculars or a magnifying glass? Have you ever had an X-ray takenof an injury? Do you need to wear glasses or contact lenses to seeclearly? Vision systems are even being developed to restore vision toblind people. In this chapter, you will take a journey into a smallworld that was discovered when the microscope was invented—theworld of the cell. Imagine you could shrink yourself and walk into atiny cell. What is it like inside a cell? It’s a fascinating journey!1. What is a cell and how do we know cellsexist?2. Are human cells, animal cells, and plantcells all the same?3. What is inside a cell, and how is a cell likea cookie factory?


5.1 What Are Cells?Look closely at the skin on your arm. Can you see that it is made of cells? Ofcourse not! Your skin cells are much too small to see with your eyes. Now lookat one square centimeter of your arm. That square centimeter contains about100,000 skin cells. Cells are so small that they weren’t even discovered until theinvention of the microscope. What are cells and how were they discovered?You are made of cellsA cell is thesmallest unit of aliving thingEach cell carriesout the livingfunctionsA cell is the basic unit of structure and function in a living thing.Your body is composed of billions of cells. You have skin cells,muscle cells, nerve cells, blood cells, and many other types as well.Each type of cell has a unique structure and function, but they allshare similarities. Figure 5.1 shows pictures of different types ofcells found in your body.A cell is the basic unit of structure andfunction in a living thing.Each cell in your body shares the characteristics of allliving things. Each cell can respond, grow, reproduce, and useenergy. Like larger organisms, cells respond to changes in theirsurroundings in ways that keep them alive. In Chapter 2 welearned that this process is called homeostasis.Figure 5.1: Different types of cellsfound in your body. Platelets are foundin your blood but are particles, not cells.92UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTIONFinding out about cellsRobert Hookediscovered cellsSome organismsare made of asingle cellAll living thingsare madefrom cellsFluorescentmicroscopyHow did we learn about cells? It all started with the invention ofthe microscope in the late 1500s. English scientist Robert Hooke(1635–1703) was the first to record his observations of cells. In1663, he took a thin slice of cork and placed it under a microscopethat he built. Cork is made from the bark of the cork oak tree, butits cells are no longer alive. Hooke made detailed sketches of hisobservations. An artist’s version of one of his sketches is shown inFigure 5.2. Hooke called each of the square structures a cellbecause they reminded him of tiny rooms.Anton van Leeuwenhoek (1632–1723) was not a scientist. He was aDutch craftsman who made lenses. Yet with skill and curiosity,Leeuwenhoek made some of the most important discoveries inbiology. He used his lenses to build a simple microscope. With hismicroscope, he looked at pond water, blood, and scrapings from histeeth. He was the first to observe single-celled protists, blood cells,and bacteria.As microscopes improved, scientists made more discoveries. In1839, two German scientists, Matthais Schleiden and TheodoreSchwann, viewed plant and animal tissues under a microscope.They concluded that all plants and animals were made up of cells.A new technique is called a fluorescent microscope. Cells usually donot glow. Scientists use fluorescent proteins to make cells glow. Thecells absorb these proteins like stains. The fluorescent microscopeuses filters that only let in light that matches the fluorescingmaterial being studied. All other types of light are blocked out. Thefluorescing areas shine out against a dark background, makingcertain cell structures glow. The mouse egg cells in Figure 5.3 havebeen treated to show DNA as a glowing blue.Figure 5.2: Robert Hooke’s sketch ofcork cells looked like this.Figure 5.3: Mouse egg cells. TheDNA is the glowing blue.5.1 WHAT ARE CELLS?93


The cell theoryCells only comefrom other cellsStatements ofthe cell theorySchleiden and Schwann’s theory was widely accepted by otherscientists. But where did cells come from? In the 1800s it wasbelieved that living things came from nonliving objects. Did cellscome from some tiny, nonliving objects? In 1855, a Germanphysician named Rudolf Virchow (1821–1902) proposed that cellscan only come from other cells.The work of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow,and others led to an important theory in life science. The celltheory explains the relationship between cells and living things.cell theory - a theory thatexplains the relationship betweencells and living things.94UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTIONSimilarities among cellsThere are manydifferent typesof cellsAll cells sharesome similaritiesSome organisms are made of only a single cell. You are made ofbillions of cells. In multicellular organisms like you, there are manydifferent types of specialized cells. For example, the cells that linethe retina of your eye have a structure and function that is verydifferent from your skin cells. About 200 different types ofspecialized cells make up the tissues and organs of your body.There are different types of cells but all cellsshare similar characteristics.Even though there are many different types of cells, they all sharesimilar characteristics (Figure 5.4). These include:1. All cells are surrounded by a cell membrane. The cellmembrane is a barrier between the inside of the cell and itsenvironment. It also controls the movement of materials intoand out of the cell.2. All cells contain organelles. An organelle is a structureinside of a cell that helps the cell perform its functions.Although all cells contain organelles, they don’t all containthe same kinds. You’ll learn more about the organelles in thenext section.3. All cells contain cytoplasm. The cytoplasm is a fluidmixture that contains the organelles. It also contains thecompounds cells need to survive such as water, salts, enzymes,and other carbon compounds.4. All cells contain DNA. The cell theory states that all cellscome from other cells. When cells reproduce, they make copiesof their DNA and pass it on to the new cells. DNA contains theinstructions for making new cells and controls all cell functions.Figure 5.4: All cells have a cellmembrane, organelles, cytoplasm, andDNA.cell membrane - a separatingbarrier that controls movement ofmaterials into and out of the cell.organelle - a structure inside of acell that helps it perform itsfunctions.cytoplasm - a fluid mixture thatcontains the organelles and thecompounds the cell needs.5.1 WHAT ARE CELLS?95


Classifying cellsTwo types ofcellsProkaryotic cellsEukaryotic cellsBased on the organization of their structures, all living cells can beclassified into two groups: prokaryotic and eukaryotic (Figure 5.5).Animals, plants, fungi, and protozoans all have eukaryotic cells.Only bacteria have prokaryotic cells.Prokaryotic cells do not have anucleus. The word prokaryotic means“before nucleus” in Greek. Scientistsbelieve that all life on Earth camefrom these cells. The oldest fossils ofbacteria are estimated to be 3.5 billionyears old. The DNA in a prokaryoticcell is bunched up in the center of thecell. The organelles are not coveredwith a membrane. All prokaryotic cellsare much smaller than eukaryoticcells.Eukaryotic cells have a nucleusand membrane-coveredorganelles. The word eukaryoticmeans “true nucleus” in Greek.The oldest fossils of eukaryoticcells are about 2 billion yearsold. There is more DNA in thesetypes of cells and it is found inthe nucleus. These cells havemembrane-covered organelles.They tend to be about ten timeslarger than prokaryotic cells.MembraneboundnucleusCellmembraneEukaryotic cellVariousmembrane boundorganellesCytoplasmprokaryotic cell - a cell thatdoes not have a nucleus ormembrane-covered organelles.eukaryotic cell - a cell that has anucleus and membrane-coveredorganelles.ProkaryoticcellsBacteriaNo nucleusDNA isbunched up inthe center of thecellEukaryoticcellsAll other cellsNucleusOrganelles notmembranecoveredMembranecoveredorganellesDNA is found inthe nucleusFigure 5.5: Comparing prokaryoticand eukaryotic cells.96UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTION5.1 Section Review1. What is the basic unit of structure and function in a living thingcalled?2. How did the invention of the microscope help scientists learnmore about living things?3. Who was the first to discover cells?4. Draw a timeline that shows the dates, discoveries, andscientists involved in the development of the cell theory.5. What are the four statements of the cell theory?6. What are specialized cells? List three examples.7. What are four similarities that all cells share?8. List the cell part for each letter on the diagram below. What isthe function of each part?1. Write a paragraph that agreesor disagrees with the followingstatement: “Muscle cells arecompletely different than nervecells.” Give the reasons for whyyou agree or disagree in youranswer.2. Explain three differencesbetween molecules and cells.3. Conduct Internet research tofind out about the largest cell inthe world.ADCB9. Classify each item below as having prokaryotic or eukaryoticcells.a. Streptococcus, a bacteria that causes strep throat.b. Yeast, a type of fungi use to make bread.c. A euglena, a one-celled protozoan that uses a whip to movearound.d. Acidophilus, a bacteria used to make yogurt.5.1 WHAT ARE CELLS?97


5.2 Cells: A Look InsideImagine a factory that makes thousands of cookies a day. Ingredients come into thefactory, get mixed and baked, then the cookies are packaged. The factory has manyparts that contribute to the process. Can you name some of those parts and theirfunctions? A cell is a lot like a cookie factory. It too has many parts that contribute toits processes. Let’s compare a cell to a cookie factory.Comparing a cell to a cookie factoryParts andfunctionsA cookie factory has many parts. The cytoplasm of a cell has manyorganelles. Figure 5.6 shows a fictional cookie factory. A typicalanimal cell and its parts are shown on the next page. Table 5.1compares a cookie factory to an animal cell. As you read thissection, refer to the table to help you remember the cell parts andtheir functions.Table 5.1: Comparing a cell and a cookie factoryProcess Cookie factory part Cell partIngredients in/products out Factory gate and doors Cell membraneControl center Manager’s office NucleusEnergy Power plant MitochondriaStorage Storage room VacuoleMaking the product Mixing/baking room RibosomeTransport of materials Conveyer belts Endoplasmic reticulumPackaging and distribution Shipping room Golgi bodyClean up and recycling Custodial staff LysosomeStructure/support Walls and studs CytoskeletonFigure 5.6: The parts of a cookiefactory.An analogy is a comparison of onething to another different thing. Thecookie factory is a good analogyfor remembering cell parts andtheir functions. After reading thissection, make another analogycomparing your school to a cell.98UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTIONDiagram of an animal cellThe picture below is a schematic drawing of an animal cell. Under a microscope, youwould not be able to see many of the organelles.5.2 CELLS: A LOOK INSIDE99


The cell membrane and nucleusLooking at cellsunder amicroscopeThe cellmembraneThe nucleus isthe control centerThe nucleolusTo make cell parts visible under a microscope, you can apply astain to the cells. A stain is a dye that binds to certain compoundsin cells. Some stains bind to proteins while others bind tocarbohydrates. Methylene blue is a stain often used to look atanimal cells. It binds to proteins and makes the nucleus of the cellstand out. It also makes individual cells stand out by staining thecell membrane (Figure 5.7).The cell membrane is a thin layer that separates the inside of thecell from its outside environment. It keeps the cytoplasm insidewhile letting waste products out. It also lets nutrients into the cell.It is made out of lipids and proteins. A cell membrane is kind oflike your skin. Your skin lets water and other materials passthrough and separates your internal parts from the outside.The most visible organelle in a eukaryotic cell is the nucleus. Thenucleus is covered with a membranethat allows materials to pass in andout. It’s often called the “controlcenter” of the cell because itcontains DNA. As you havelearned, DNA is the hereditarymaterial that carries all of theinformation on how to make the cell’sproteins. You might say it’s kind of like a recipe book.If you look closely at the nucleus of a cell under a microscope, youmay see an even darker spot. This spot is called the nucleolus. Itacts as a storage area for materials that are used by otherorganelles.Figure 5.7: These human cheek cellshave been stained with methylene blue.How many cells do you see? Can youidentify the nucleus in each cell?Cells are not flat objects like theyappear in this text. They are threedimensionaljust like you are. Acell that appears circular on paperis really shaped like a ball.Find everyday objects that remindyou of the different organellesinside of a cell. Collect thoseobjects and make a table listingthe object and the organelle itreminds you of.100UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTIONOrganelles and their functionsSeeing the otherorganellesEven with a powerful microscope, it’s difficult to see organellesother than the nucleus. Scientists use different techniques likefluorescent microscopy to make organelles stand out. Figure 5.8shows cells that have been treated to make the mitochondria standout (the red dots).Many discoveries about organelles were made using an electronmicroscope. This type of microscope uses tiny particles calledelectrons, instead of reflected light, to form images.Mitochondria: thepowerhouse ofthe cellVacuoles:storage areas ofthe cellMitochondria are called the“powerhouses” of cells becausethey produce much of the energya cell needs to carry out itsfunctions. They are rod-shapedorganelles surrounded by twomembranes. The innermembrane contains many folds,where chemical reactions takeplace. Mitochondria can onlywork if they have oxygen. The reason you breathe air is to getenough oxygen for your mitochondria. Cells in active tissues—likemuscle and liver cells—have the most mitochondria.Mitochondria produce much of the energy acell needs to carry out its functions.In some animal cells, you will find small, fluid-filled sacs calledvacuoles. A vacuole is the storage area of the cell. Vacuoles storewater, food, and waste. Plant cells usually have one large vacuolethat stores most of the water they need.Figure 5.8: These mouse cells havebeen prepared to show mitochondriaand the nucleus. The mitochondriaappear as glowing red structures.mitochondria - an organelle thatproduces much of the energy acell needs to carry out itsfunctions.vacuole - an organelle that storesfood, water, and other materialsneeded by the cell.5.2 CELLS: A LOOK INSIDE101


EndoplasmicreticulumRibosomesGolgi bodiesLysosomesCytoskeletonThe endoplasmic reticulum (ER)is a series of tunnels throughoutthe cytoplasm. They transportproteins from one part of the cellto another. You can think of theER as a series of folded andconnected tubes. There aredifferent places to enter and exitin various locations.If you look closely at the ER, you can sometimes see little roundgrains all around it. Each of those tiny grains is an individualribosome. Ribosomes are the protein factories of the cell. Whenribosomes make proteins, they release them into the ER. Someribosomes are not attached to the ER, but float in the cytoplasm.Golgi bodies receive proteins and other compoundsfrom the ER. They package these materials anddistribute them to other parts of the cell. They alsorelease materials outside of the cell. The numberand size of Golgi bodies found in a cell dependson the quantity of compounds produced in thecell. The more compounds produced, the moreand larger Golgi bodies there are. For example, alarge number of Golgi bodies are found in cells that producedigestive enzymes.Lysosomes contain enzymes that can break things down.Lysosomes pick up foreign invaders such as bacteria, food, and oldorganelles and break them into small pieces that can be reused.The cytoskeleton is a series of fibers made from proteins. Itprovides structure to the cell and gives it its shape. Figure 5.9shows a cell that has been treated so the cytoskeleton stands out.endoplasmic reticulum - anorganelle that transports proteinsinside of the cell.ribosome - an organelle thatmakes proteins.Golgi body - an organelle thatreceives proteins, packages them,and distributes them.lysosome - an organelle thatcontains enzymes that breakthings down to be reused bythe cell.cytoskeleton - a series ofprotein fibers inside of a cellthat give structure and shapeto the cell.Figure 5.9: This cell was treated tomake the cytoskeleton stand out.102UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTIONDiagram of a plant cellPlant cells are different from animal cells. Here is a diagram of a typical plant cell.5.2 CELLS: A LOOK INSIDE103


How plant cells are different from animal cellsFigure 5.10 shows that plant and animal cells look very different.Their differences are described below.Plant cells havechloroplastsPlant cells have alarge, centralvacuolePlant cells have acell wallPlant cells have chloroplasts, but animal cells do not. Achloroplast is an organelle that contains a pigment calledchlorophyll. Chloroplasts are organelles that convert light energyinto chemical energy in the form of molecules. This process iscalled photosynthesis.Plant cells have a large central vacuole that stores cell sap. Themajor component of cell sap is water. Cell sap also consists ofsugars, amino acids, and ions. When these vacuoles are full ofcell sap, they help give plant cells their structure and rigidity.Plant cells have a cell wall, but animal cells do not. The cell wall ismade of a carbohydrate called cellulose. Cell walls providestructure and support for the plant. Unlike the cell membrane, thecell wall is able to withstand high internal pressure. The buildupof water inside the central vacuole provides pressure against thecell wall. When a plant needs water it wilts because the centralvacuoles in its cells are empty. They no longer push against thecell walls to keep the plant upright. Watering the plant restoreswater in the central vacuoles.Figure 5.10: How are plant cellsdifferent from animal cells?chloroplast - an organelle thatconverts light energy into chemicalenergy in the form of molecules.cell wall - the outer layer of aplant cell that is made fromcellulose and makes plant cellsrigid.104UNIT 2 CELL BIOLOGY


CHAPTER 5: CELL STRUCTURE AND FUNCTION5.2 Section Review1. Name the correct organelle for each function in the table below.OrganelleFunctionProduces much of the energy a cellneeds to carry out its functionsMakes proteins.Controls all activities of the cell andcontains the hereditary materialPackages proteins and distributesthem to other parts of the cellLets materials pass into or out of the cellStores water, food, and wastesTransports proteins inside of the cell2. The plant cell wall is made of:a. glucoseb. proteinc. cellulosed. lipids3. A Venn diagram shows how two or more things are similarand different. Place the organelles into the Venn diagram inFigure 5.11. What do your results tell you about the differencesbetween plant and animal cells?4. What is the function of the cell wall? Why do plant cells need acell wall?What effect on the function of acell would occur if one of thefollowing organelles was missing?Write a sentence for eachorganelle.1. ribosome2. lysosome3. vacuole4. mitochondria5. chloroplast6. cell membraneFigure 5.11: Complete the Venndiagram for question 3.5.2 CELLS: A LOOK INSIDE105


Organ TransplantsChapter 5 Connection106How many ways do living things protect themselves? Youcan probably think of dozens of examples. Roses have thorns.Rabbits are quick. Pigeons fly in flocks. Have you everthought about this? What is the most important way thatmany living things, including people, protect themselves?The answer might surprise you.All living things must protect themselves against disease.Like other living things, people are under constant assaultfrom bacteria, viruses, and other organisms. Our immunesystems fight off these organisms.What happenswhen a foreign cellenters your body?It causes a quickresponse fromyour immunesystem. A varietyof cells attack theinvader. At theheart of yourimmune systemare cells calledlymphocytes. These are a type of white blood cell.Lymphocytes can grab onto foreign cells and help removethem from your body.For your immune system, the world divides into “us” and“them.” “Us” means every cell in your body. “Them” meansalmost everything else on Earth. The immune systemattacks “them.” This can be a problem with organtransplants.The problem with transplantsHindu doctors in South Asia may have transplanted skin2,600 years ago. Such grafts took skin from one part of aperson’s body. It replaced damaged skin in another part ofthe same person’s body. This is still done today.The immune system ignores this kind of transplant. Thetissues “match” exactly. All of the cells came from the samebody. For the same reason, heart bypass operationsuse blood vessels fromthe patient’s ownbody to replaceblocked heartarteries.Modernmedicine isable totransplantmany organsbesides skinand bloodvessels.Kidneys, livers,hearts, and even lungshave been transplanted.Transplants save people’s lives. In each case, the patient’simmune system must be overcome. The immune system maysee the transplant as an invader. This is called “rejection.”Antigens are on the surface of cells. They tell your immunesystem whether a cell is “us” or “them.” Two types ofantigens cause rejection. One is found on red blood cells. Theother is called transplantation, or histocompatibility,antigens. These are found on every cell in your body exceptred blood cells. The main transplantation antigens are calledthe human leukocyte antigens, or HLA. Your genes


determine your HLA. Only identical twins have the samegenes. An organ could be transplanted from one identicaltwin to another without rejection. In every other case,doctors need to match organs. Doctors look for as close amatch as they can between the HLA of the patient and theperson who donated the organ.Tissue-matchingMatching antigens is more often called “tissue matching” or“tissue typing.” Both blood type andHLA are matched as closely aspossible.Lymphocytes are used for HLAmatching. Blood typing is simple.But there are many more HLAantigens. Tissue matching is morecomplicated than blood typing. Insimple terms, lymphocytes from thedonor and the patient are tested.The same chemicals are used oneach set of cells. A certain chemicalmay kill both. Then the donor andpatient have that one antigen incommon. The lymphocytes may both survive. Then the donorand patient both lack that antigen. The lymphocytes of justthe donor may be affected, but not the patient. The HLA doesnot match.This process is repeated many times to test for differentantigens. Even when the donor and patient seem to matchwell, there is a final test. Lymphocytes from the donor aretested against blood serum from the patient. If this test fails,the transplant is usually not done.These tests are done in a laboratory. Trained technicians dothe tests under the direction of a pathologist. This medicaldoctor specializes in body tissues and fluids.The future of transplantsA transplant has the best chance of success when the donorand the patient are related. The chance of a complete matchis best between siblings. Brothers and sisters may donatebone marrow or a kidney to one another. Most othertransplants, however, come from people who donate theirorgans when they die.An exact tissue match can only happen with identical twins.Most transplant patients musttake drugs to stop their immunesystems from rejecting the newtissue. There are side effects withthis approach.Many more people could behelped if organs could betransplanted as easily as blood.One idea is to change a patient’simmune system so that it wouldstill fight infections but not attacka donated organ.Scientists have made this work inlaboratory mice. In 2005, Navydoctors made it work with monkeys. If it can work safely inpeople, organ transplants might become the easiest way totreat many diseases in the future.Questions:1. What specialized cells are the “heart” of your immunesystem?2. What doctors are believed to have done the first organtransplants, and when did they do them?3. Why do you think a living thing’s immune response is calledits “most important” way of protecting itself?4. How might organ transplants in the future be done as easilyas blood is transfused today?Chapter 5 ConnectionUNIT 2 CELL BIOLOGY107


Building a Scale Model of a CellChapter 5 ActivityCells appear in all shapesand sizes. In animals, cellscan be long like the motorneurons that run from thetips of your toes to the baseof the neck. Other cells inyour body can be small likethe red blood cells. Cellmodels are a good way tohelp you identify cellstructures. Often it is not clear how the size of the cell isrelated to the size of the organelles. In this activity, you willexplore the relationship of cell size to organelle size bycreating a scale model.What you will do1. Complete the table (right). Use a scale factor of1 micrometer = 1 centimeter. The calculation for thediameter of the cell is completed for you.2. Obtain a large sheet of paper from your teacher.3. Measure the diameter of the cell (35 centimeters) anddraw a circle on your paper. This will be the outline ofyour animal cell. Cut out the circle out of the paper.4. Using your calculation, make a nucleus to scale using thecolored-construction paper your teacher has provided.5. Make and add the rest of the organelles. Be sure to usethe animal cell diagram on page 99 as a guide in makingyour organelles. For example, you could make a golgibody that consists of 5 separate parts, 7 × 2 micrometerseach.6. Once the model is complete, label the organelles. Or youmay wish to make a key that identifies each organelle.OrganelleAverage Size(μm)Scaling Factor(1 μm = 1 cm)ModelSize(cm)Cell Diameter 35 35 μm × 1 cm/μm 35Nucleus 5Mitochondria 6×2Lysosome 2EndoplasmicReticulum5×10Golgi Body 7 × 2Vacuole 2Ribosome .02Applying your knowledgea. What is the smallest organelle in a typical animal cell?b. What is the largest organelle in a typical animal cell?c. How is your model of the cell different than models theteacher used in class, or models you may see in a textbook?d. This method does not apply only to cells. Can you think ofother examples where scale models are used?e. How might you build a 3-dimensional scale model of acell? With a classmate, propose a method for creating ascaled 3-dimensional model of a cell with all theorganelles. What types of things could one use torepresent the cell boundaries? What things might one useto represent the organelles? Begin by writing up yourideas in a proposal. Your teacher may ask you to buildyour model as a project.108


Chapter 5 AssessmentVocabularySelect the correct term to complete the sentences.cell membrane cytoskeletonmitochondriacell wallendoplasmic reticulum organellenucleusgolgi bodyprokaryoticcytoplasmlysosomeribosomeSection 5.11. Bacteria are _____ cells.2. The _____ controls what enters and exits the cell.3. A structure inside a cell that does a certain job is called an_____.4. The fluid mixture with organelles and other vitalcompounds in cells is the _____.5. Eukaryotic cells all have a _____ that contains DNA.Section 5.26. The _____ is the organelle that transports materials likeproteins around the cell.7. Fibers inside the cell that give structure and shape arecalled the _____.8. Muscle cells have a lot of _____ to produce the large amountsof energy necessary to do their work.9. A _____ is a protein factory in the cell.10. Enzymes found in a _____ are used to break down old cellparts that are then recycled by the cell.11. Proteins move from the ribosome to the _____ for packagingbefore distribution around the cell.12. Animal cells can change shape to move because they don'thave a _____, which is what makes plant cells rigid.ConceptsSection 5.11. Which of the following is not part of the cell theory?a. Cells only come from existing cells.b. All of an organism's life functions occur within cells.c. The two major types of cells are prokaryotic cells andeukaryotic cells.d. All living things are made of one or more cells.2. Identify each characteristic as either a feature ofprokaryotic cells (P) or as a feature of eukaryotic cells (E).a. _____ name means “before nucleus” in Greekb. _____ believed to have originated 2 billion years agoc. _____ DNA is contained in nucleusd. _____ larger of the two types - 10 times the size of theothere. _____ have organelles without membrane coversSection 5.2Match the organelles to the most appropriate item that performsthe same function to complete these analogies._____ 3. ER a. nutshell_____ 4. cell wall b. warehouse_____ 5. vacuole c. brain_____ 6. cell membrane d. highway7. nucleus e. skin8. Which part of the cell is like a recipe book?a. nucleolusb. DNAc. cell membraned. none of the above9. The ____________________ is the largest organelle in the cell.CHAPTER 5 CELL STRUCTURE AND FUNCTION109


10. Cells can only have one of certain organelles like thenucleus. Which organelles can a cell have many of the samekind? Explain your answer.11. Which organelle would cause a lot of damage to the cell if itwere to break open? Why?12. Potato cells don't have chloroplasts. If you saw these cellsunder the microscope, how could you tell that they wereplant cells?Math and Writing SkillsSection 5.11. Imagine that you are Anton van Leewenhoek and you havejust observed the first blood cells, bacteria, and single-celledprotists. Write a letter to a friend describing your amazingdiscoveries.2. Write an imaginary dialogue that could have taken placebetween Matthais Schleiden and Theodore Schwann afterthey observed plant and animal tissue under a microscope.3. Many of the cells in your body are 0.01 mm long. Use thatmeasurement to complete these calculations.a. An amoeba - a unicellular protist - is 1 mm long. Howmany body cells would you have to stack end to end toequal the size of an amoeba?b. Figure out what your height is in millimeters bymultiplying your height in meters by 1000. How manybody cells would you have to stack end to end to equalyour height?c. The length of a swimming pool is 25,000 mm. Howmany body cells would you have to stack end to end toequal the length of the pool?d. Prokaryotic cells are approximately 1/10 the size ofeukaryotic cells. How big are prokaryotic cells?4. If you were trying to classify an unknown organism bylooking at its cells, what could its cells tell you?Section 5.25. Describe what goes on in a typical animal cell. Be sure tomention all the organelles listed in the text.6. Which organelles does a spinach cell have that a rabbit celldoes not? Explain your answer.7. Explain the connection between a wilted plant and cell partslike the vacuole and the cell wall.Chapter ProjectCellular songCells have organelles with weird names like golgi body andendoplasmic reticulum. It is often helpful to invent a way to helpyou remember the names of the structures and their functions.Create a song or poem about cell structure, using the guidelinesbelow. Record the song or poem and play it back for the class, orperform it live. If you don't like solo work, join some classmatesand do this as a group project. Make sure everyone contributesverses to the song or poem!1. Choose one type of cell, either a plant cell or an animal cell.2. Choose a popular song for the melody or rap. If you create apoem, make the verses rhyme.3. The song or poem must include each structure listed on theanimal or plant cell diagram in your book. In addition tonaming the structures, you must use the song or poem tohelp you remember the function of each structure.4. Submit your creation for approval, memorize it, and thenshare the song or poem with your classmates. When it comestime for a written test on cell structure, you might behumming a tune to help you remember the answers!110CHAPTER 5 CELL STRUCTURE AND FUNCTION


6.1 The Structure and Function of the Cell MembraneThe cell membrane is kind of like a soap bubble (Figure 6.1). A soap bubble consistsof a thin, flexible membrane. The soapy membrane seals the inside air from theoutside. Likewise the cell membrane is a thin, flexible layer that seals the inside ofthe cell from its outside environment. In this section, you’ll learn about the structureand function of the cell membrane.A closer look at the cell membraneThe functions ofthe cellmembraneThe structure ofthe cellmembraneThe cell membrane has many functions. It protects the cell fromits environment and takes in food and other compounds that thecell needs. It also gets rid of waste from inside of the cell. The cellmembrane even allows cells to communicate and interact.The cell membrane is made of several types of molecules. Lipidmolecules form a double layer. This creates a thin, fluid layer likea soap bubble. Embedded protein molecules can move aroundwithin this layer. Carbohydrates attached to some proteins faceoutward. Some of these serve as “identification cards” so cells canrecognize each other.Figure 6.1: Soap bubbles are similarto cell membranes.112UNIT 2 CELL BIOLOGY


CHAPTER 6: CELL PROCESSESDiffusionWhat isdiffusion?How diffusionworks in a cellCells live in a watery environment. The cytoplasm is 80% water.Every cell in your body is also surrounded by a watery solution.Solutions make it easier for molecules to move into or out of thecell. Molecules move across the cell membrane by a process calleddiffusion. Diffusion is the movement of molecules from areas ofgreater concentration to areas of lesser concentration.In order for diffusion to occur, there must be an unequal numberof molecules on each side of the cell membrane. If there are moremolecules on the outside of the membrane compared to the inside,the molecules will move to the inside of the cell until there is anequal number of molecules on both sides. Can you predict what willhappen if there are more molecules on the inside of the cell?diffusion - the movement ofmolecules from areas of greaterconcentration to areas of lesserconcentration.Observing diffusion1. Fill a clear glass with water.2. Carefully add a drop of foodcoloring to the water.3. Observe the glass every2 minutes and record yourobservations in your journal.Not all moleculescan pass throughby diffusionMolecules move into or out of the cell untilthere is an equal number on both sides of thecell membrane.Not all molecules can move across the cell membrane by diffusion.You can compare the cell membrane to a tea bag. Only smallerparticles can pass through the tea bag. Larger particles are leftinside of the bag. The same is true of the cell membrane. Smallmolecules like oxygen and carbon dioxide can pass through. You’lllearn how larger molecules diffuse later in this chapter.4. What happens to the foodcoloring? Explain what ishappening at the molecularlevel.5. You observed a process calleddiffusion. How might the cellmembrane use diffusion tomove molecules in or out?6.1 THE STRUCTURE AND FUNCTION OF THE CELL MEMBRANE113


OsmosisWhat is osmosis?Cells take inwater by osmosisMore watermoleculesoutsideWater moleculesequal onboth sidesFewer watermoleculesoutsideAnimal andplant cellsWater molecules are small enough to pass through the cellmembrane by diffusion. Osmosis is the diffusion of water acrossthe cell membrane. Like other molecules, water moves from areasof greater concentration of water molecules to areas of lesserconcentration.When you put a cell into a solution, it will either take in water,stay the same, or lose water. What happens depends on theamount of water in the solution. For example, a sugar solution(sugar dissolved in water) contains fewer water molecules than thesame amount of pure water.If the solution outside the cell has more water molecules thaninside the cell, the cell gains water. Water molecules are free topass across the cell membrane in both directions, but more watercomes into the cell than leaves. The cell swells up (Figure 6.2, top).If the solution outside the cell has the same amount of watermolecules as inside the cell, the amount of water inside the cellstays the same. Water crosses the membrane in both directions,but the amount going in is the same as the amount going out.Thus, the cell stays the same size (Figure 6.2, middle).If the solution outside the cell has fewer water molecules thaninside the cell, the cell loses water. Again, water crosses the cellmembrane in both directions, but this time more water leaves thecell than enters it. The cell shrinks (Figure 6.2, bottom).If animal cells take in too much water they can burst. That’s whyyour cells are surrounded by a solution that has the same amountof water as inside the cell membrane. Plant cells can take in morewater than animal cells because of their strong cell walls.osmosis - the diffusion of wateracross the cell membrane.Figure 6.2: When you put a cell intoa solution, one of three things canhappen.114UNIT 2 CELL BIOLOGY


CHAPTER 6: CELL PROCESSES6.1 Section Review1. List four functions of the cell membrane.2. How is the cell membrane like a soap bubble?3. What is diffusion? Name one example of diffusion.4. What is osmosis? What structure in a plant cell helps protect itfrom osmosis?5. For each situation below, state whether water will move intothe cell, move out of the cell, or stay the same.The owner of this plant wateredit with salt water by mistake. Thepictures below show whathappened to the plant at 8:00 a.m.,12:00 p.m., and 4:00 p.m.6. How is active transport different from diffusion?7. Name two situations in which a cell would need to use activetransport instead of diffusion.8. Explain why cells are so small.9. Which figure below has the highest surface-area-to-volumeratio? Explain your reasoning.1. Describe what happened to theplant and its cells over time.2. Explain why you think thesethings happened. State yourexplanation as a hypothesis.3. Design an experiment to test ifyour hypothesis is correct.6.1 THE STRUCTURE AND FUNCTION OF THE CELL MEMBRANE117


6.2 Cells and EnergyTo stay alive, you need a constant supply of energy. You need energy to move, think,grow, and even sleep. Where does that energy come from? It all starts with the sun.Plant cells store energy from the sun in the form of molecules. In this section you’lllearn about how cells store and release energy.What is photosynthesis?Solar cells andchloroplastsHow does a tinyseed grow into amassive tree?Photosynthesisis a chemicalreactionA solar calculator has solar cells that convert light energy intoelectrical energy. The electrical energy powers the calculator. Aplant cell has chloroplasts that also convert energy. Chloroplastsare where photosynthesis occurs. Photosynthesis is a processwhere plants use the energy of sunlight to produce energy-richmolecules (carbohydrates).Photosynthesis takes place in thechloroplasts.Before our knowledge of photosynthesis, gardeners wondered howa tiny seed could grow into a massive tree. Where did all of thatmass come from? In the 1600s, a Flemish scientist named Jan VanHelmont (1580–1644) conducted an important experiment. Hegrew a willow tree in a carefully weighed amount of soil. Henoticed that the mass of the soil barely changed while the mass ofthe tree greatly increased. He concluded that the extra mass camefrom water, not from the soil.Later experiments carried out by other scientists showed thatplants use carbon dioxide (from the air) and water to make asimple carbohydrate (glucose) and oxygen. This chemical reaction(photosynthesis) takes place only in the presence of light(Figure 6.6).photosynthesis - a processwhere plants use the energy ofsunlight to produce carbohydrates.Figure 6.6: The chemical reaction ofphotosynthesis. What are the reactantsof the reaction? What are the products?118UNIT 2 CELL BIOLOGY


CHAPTER 6: CELL PROCESSESLight and colorVisible lightLight is a waveThe Sun provides Earth with a steady source of light. Your eyesperceive sunlight as white light. However, it is really made up ofdifferent colors of light. The colors that make up sunlight are calledvisible light. There are other forms of light we cannot see such asultraviolet and infrared light.Light is a wave, like a ripple on a pond. Waves can be described bytheir wavelength (the length from peak to peak), and energy. Lightis part of a continuum of waves known as the electromagneticspectrum. Light waves have very short wavelengths. They rangefrom 800 nm (red light) to 400 nm (violet light). One nanometer(nm) is equal to one-billionth of a meter!Figure 6.7: A prism splits lightinto all of its colors. All of the colorsof light have different energies andwavelengths.ColorA prism splits white light into all of its colors. Color is how weperceive the energy of light. All of the colors of visible light havedifferent energies. Red light has the lowest energy and violet lighthas the highest energy. As we move through the rainbow from redto violet, the energy of the light increases (Figure 6.7).color - how we perceive theenergy of light.6.2 CELLS AND ENERGY119


ChlorophyllWhy most plantsare greenLight isnecessary forphotosynthesisPlants reflectsome light tokeep coolWhy leaveschange colorA pigment is a molecule that absorbs some colors of light andreflects others. Chlorophyll is the main pigment used inphotosynthesis. It is found inside the chloroplasts of plant cells.Chlorophyll absorbs mostly blue and red light, and reflects greenlight. This is why most plants look green.The vertical (y) axis of the graph in Figure 6.8 shows thepercentage of light absorbed by a plant. The horizontal (x) axisshows the colors of light. The curve shows how much and whichcolors of visible light are absorbed by plants. The graph shows thatplants need red and blue light to grow. Based on this graph, canyou explain why plants look green? Do you think a plant wouldgrow if it were placed under only green light?Why don’t plants absorb all colors of light? The reason is thesame reason you wear light-colored clothes when it’s hotoutside. Like you, plants must reflect some light to avoidabsorbing too much energy and overheating. Also, certaincolors of visible light have just the right amount of energy tomake photosynthesis occur. Ultraviolet light has more energybut would cause other chemical reactions. Infrared light hastoo little energy to make photosynthesis occur.In some parts of the world, the leaves of some plants, such assugar maple trees, turn brilliant red or gold in the autumn.Chlorophyll masks other plant pigments during the spring andsummer. In the autumn photosynthesis slows down. Chlorophyllbreaks down and red, orange, and yellow pigments in the leavesare revealed!pigment - a molecule thatabsorbs some colors of lightand reflects others.chlorophyll - the main pigmentused in photosynthesis thatabsorbs blue and red light andreflects green light.Figure 6.8: Plants need to absorblight to grow. The plant pigmentchlorophyll absorbs red and blue light,and reflects green light. This is whyplants look green!120UNIT 2 CELL BIOLOGY


CHAPTER 6: CELL PROCESSESCellular respirationWhat is cellularrespiration?The reactantsand products ofcellularrespirationCellularrespiration andenergyYour cells get the energy they need from the food you eat. Yourdigestive system breaks down food into molecules. Your cellsconvert those molecules into a form of energy they can use. Cellularrespiration is the process in which the chemical bonds of energyrichmolecules (like glucose) are converted into a form of energythat cells can use. In eukaryotic (including animal and plant) cells,cellular respiration takes place in the mitochondria.Cellular respiration takes place in themitochondria.Respiration is the process of breathing. Cellular respiration is notthe same thing as breathing but they are closely related. Youbreathe in to get oxygen. You breathe out to get rid of carbondioxide. Cellular respiration is a chemical reaction that usesoxygen and glucose to produce carbon dioxide, water, and energy(Figure 6.9). When you breathe in, you take in the oxygen your cellsneed for cellular respiration. When you breathe out, you get rid ofthe carbon dioxide that your cells produce during cellularrespiration. Try breathing onto a mirror or glass surface. Can yousee evidence of another product of cellular respiration?During cellular respiration, some energy is stored and some isreleased. Energy is stored in a molecule called ATP. ATP is amolecule that stores and transfers chemical energy within cells.It is used to power cell functions such as muscle contractions, nerveimpulses, and molecule-building. Energy released from cellularrespiration is often given off in the form of heat. Your body is warmbecause of the released energy from cellular respiration.cellular respiration - theprocess in which the chemicalbonds of energy-rich moleculesare converted into a form ofenergy that cells can use.ATP - a molecule that stores andtransfers energy within cells.Figure 6.9: The chemical reaction forcellular respiration. What are thereactants? What are the products?6.2 CELLS AND ENERGY121


Comparing photosynthesis and cellular respirationComparing the reactions for photosynthesis and cellularrespiration shows how living things on Earth are connected.The reactants in photosynthesis are the products in cellularrespiration. The reactants in cellular respiration are the productsin photosynthesis. The elements involved are carbon, hydrogen,and oxygen.Write the story of a carbonatom as it travels throughphotosynthesis and cellularrespiration. Include the followinginformation in your story:• the molecules in which thecarbon atom is found.• the organisms, cells, andorganelles through which ittravels.Be creative!122UNIT 2 CELL BIOLOGY


CHAPTER 6: CELL PROCESSES6.2 Section Review1. How are solar cells and chloroplasts similar?2. What is the electromagnetic spectrum? Which part of theelectromagnetic spectrum do plants use for photosynthesis?3. When white light is passed through a prism, what happens?4. The chemical reaction forphotosynthesis is shown tothe right. Use it to answerquestions a through d.a. Name the reactants inthe reaction.b. Name the products inthe reaction.c. What is the function ofsunlight in the reaction?d. What is the function ofchlorophyll?5. Where does cellularrespiration take place?6. What are the similaritiesbetween cellularrespiration and respiration(breathing)? What are thedifferences?7. What is the function of ATP in cellular respiration?8. How are photosynthesis and cellular respiration related?9. Do you think animals could survive without plants? Explainyour answer.All plants that use sunlight to growhave chlorophyll, but some do notlook green. Come up with ahypothesis to explain thisobservation.1. Arrange the following colorsfrom highest to lowest energy:green, yellow, red, blue,orange, violet2. Arrange the following types ofelectromagnetic waves fromlongest to shortest wavelength:visible light, radio waves,ultraviolet light, microwaves,gamma rays, infrared waves6.2 CELLS AND ENERGY123


Chapter 6 ConnectionAmazing Cells!Did you know your body is made of trillions of cells? Thereare millions of different types. Where did all of thesedifferent types come from? Part of the answer is a specialtype of cell called stem cells.Many living things need stem cells including animals andplants. An organism that is not fully developed is called anembryo. In animal embryos, stem cells can develop intodifferent types of cells. Your body has over 200,000 differenttypes of cells. It has blood cells, muscle cells, skin cells, andstomach cells just to name a few. Each type of cell has itsown structure and function.The process of differentiationAll stem cells have some certain properties:• Stem cells divide to make more stem cells.• Stem cells also have the ability to develop into differenttypes of cells.A stem cell divides into two daughter cells. Each daughtercell is identical to the original parent cell. When mature,these cells also divide. This is how embryos get a supply ofstem cells. A growing embryo needs a lot of stem cells todevelop tissues and organs. In the laboratory, starting with afew stem cells, scientists have grown millions in a fewmonths.So how dostem cellschange intoother types ofcells?Scientists areParent cell Two daughter cells studying thisproblem.Something called a signal tells stem cells to become differenttypes of cells. Genes are pieces of DNA that carryinformation from the parent cell to the offspring cells. Thegenes inside stem cells provide internal signals. Theenvironment outside of the cell provides external signals.The cell's environment includes chemicals from other cells.Different types ofspecialized animal cellsThere are two main types ofanimal stem cells. More thantwenty years ago, scientistsextracted stem cells from theembryos of mice. These stemcells are described asembryonic. The other maintype of stem cells is describedas adult. Embryonic stemcells and adult stem cells arevery different.Embryonic stem cells can divide to make more stem cells.They wait for a signal. Then they start producing specializedcells. These specialized cells form the tissues, which in turnform the organs.124


Embryonic stems cells are like new players on a soccer team.Until the players are trained, they are reserves. They havethe potential to do a lot of different things. Once they aretrained, they become specialized in a position. The playersmight be defenders or forwards. They might play goalie ormid field. Similarly, embryonic stem cells are generic cells atfirst. They get “training” from a signal. Then they developtissue for the kidneys, liver, or other organs.While the main job of embryonic stem cells is growth, themain job of adult stem cells is repair. They do not have asmuch potential as embryonic stem cells. They seem toalready carry genetic information that determines whichtype of cells they can become. They exist alongside the typesof cells they can produce. Adult stem cells in the skin, forexample, develop into skin cells to help new skin grow afteran injury.The potential for treating diseasesScientists think stem cells may help treat diseases. Can youthink how this might work? Embryonic stem cells candevelop into many other types of cells. If the right signalscan be discovered, these cells might be able to replace orrepair diseased tissue. Scientist's hope that diseases such asdiabetes and heart disease may be treated this way someday.Adult stem cells are already used in medicine. For 30 years,adult stem cells have been used in bone marrow transplants.The potential of adult stem cells is more limited, butscientists hope to use them to fight diseases. For example,research in mice indicates that putting adult stem cells intoa damaged heart may help repair heart tissue.Scientists are trying to better understand what triggers thedifferentiation of stem cells. As knowledge andunderstanding of stem cells increase, so does the potentialfor many new disease therapies.Questions:1. What are the properties of stem cells?2. Explain how stem cells change into different cell types.3. What is the major difference between embryonic stemcells and adult stem cells?4. How are adult stem cells used in medicine today?UNIT 2 CELL BIOLOGY125Chapter 6 Connection


Chapter 6 ActivityMaking a Concept MapA concept map is a way to represent informationvisually. A concept map consists of nodes that containwritten concepts. The nodes are connected with lines toto show relationships. The lines are labeled with anarrowhead to describe the direction of the information.In this activity you will create a concept map thatexplains how cells get and use energy. Your conceptmap should address the following question: How doanimal and plant cells use energy for life’sprocesses?What you will do1. Write the concepts below on separate index cards orsticky notes so they can be moved around.mitochondria growth ATP energychloroplasts plant cell food carbon dioxideoxygen carbohydrates energy pigmentsphotosynthesis carbon sunlight plantsanimals aircellularrespirationchlorophyll2. Obtain a large sheet of paper or poster board from yourteacher.3. Rank the concepts in order by placing the most generalconcepts at the top to the most specific term at thebottom. Think about the focus question to help rank thequestion. Begin with only one to three of the most generalconcepts at the top of the map.4. Choose two to four sub concepts to place under eachgeneral concept.5. Connect the concepts by lines. Label the lines with one ora few linking words that define the relationship betweenthe two concepts. These should read as a statement.Draw arrow heads to show the direction of theinformation.6. Look at your map and revise any part if necessary.7. Look for cross links between concepts in different sectionsof the map. Draw and label these lines.8. Present your concept map to the class and compare it toothers.Applying your knowledgea. Explain the relationship between photosynthesis andgrowth.b. Do plants take in organic food substances such as starch,sugar or protein from the soil?c. As a plant grows it gains weight (mass). Where does thisweight come from?d. Where is carbon dioxide and water absorbed by mostplants?e. What is the role of chlorophyll in a plant cell?f. How does the food you eat aid in cellular respiration?g. How did your concept map change as you made it?h. Revise your concept map again if you wish, after yourclass discussion.126


Chapter 6 AssessmentVocabularySelect the correct term to complete the sentences.chlorophyllphotosynthesis active transportpigmentATPosmosiscellular respirationdiffusionSection 6.11. Movement of molecules that requires energy is called ____.2. ____ is a kind of diffusion that involves water moving acrossthe cell membrane.3. Osmosis and ____ are two types of passive transport becausethey do not require energy.Section 6.24. ____ stores and transfers chemical energy in cells.5. Plant cells perform ____ to store energy from the sun in theform of molecules.6. When ____ breaks down in the autumn, leaves change coloras red, orange, and yellow pigments become visible.7. ____ uses oxygen and glucose to produce carbon dioxide,water, and energy.8. Chlorophyll is a ____, which is a molecule that absorbs somecolors of light and reflects others.ConceptsSection 6.11. Draw and label a diagram of the cell membrane.2. How do different cells recognize each other?3. Distinguish between diffusion and osmosis.4. Identify each situation as an example of diffusion, osmosis,or active transport.a. making a cup of teab. leftover salad wilting in the refrigeratorc. smoke escaping from the chimneyd. pumping up a tire with aire. stained cotton t shirt soaking in sinkf. smell of perfume spreading through the roomSection 6.25. Why do plants look green?6. How are breathing and cellular respiration related?7. Do plant cells need to carry out respiration? Explain.8. Create a table that compares photosynthesis and cellularrespiration including: definitions, reactants, products, whatorganisms perform the process, and where it occurs in thecell.Math and Writing SkillsSection 6.11. The concentration of a solution can be expressed as a ratio -a comparison of two numbers. For example if you dissolved10 grams of sugar in one liter of water, you could say theconcentration as a ratio - 10 g: 1L or 10g/L. Calculate theseconcentrations and ratios.a. You dissolve 120 g of sugar in 2 L of water. What is theconcentration per liter? State the concentration as aratio.b. You dissolve 50 g of salt in 3 L of water. What is theconcentration per liter? State the concentration as aratio.CHAPTER 6 CELL PROCESSES127


2. Helium balloons float because helium is lighter than themixture of gases in the surrounding air. Use what youlearned about diffusion to explain why helium balloonsdeflate after a few days. How is the balloon like the cellmembrane?3. This chart shows the time (minutes) that it took for asubstance to diffuse completely in a liquid of increasingtemperature. (degrees Celsius). Use the data to help answerthe questions and predict the affect of temperature on therate of diffusion.a. At what temperature was the rate of diffusion thefastest?b. At what temperature was the rate of diffusion theslowest?c. How does temperature affect the rate of diffusion?Section 6.2Temperature(degrees Celsius)Time for diffusion(minutes)10 820 430 240 1.850 1.660 1.470 1.280 190 .8100 .54. Fill in the greater than (>) or less than (


Chapter 7The Microscopic WorldIn previous chapters, you learned what cells are like on the inside andhow they work. Most living things contain many cells. The humanbody contains trillions of cells. Did you know that some livingorganisms are made up of only ONE cell? Some of these single-celledcreatures have been found living in volcano openings, polar ice, andeven inside a human stomach! In this chapter, you will learn howorganisms made up of only one cell carry out necessary life functions.You’ll also learn about invaders of cells called viruses. Viruses aren’tconsidered alive by most scientists. They invade cells and turn theminto factories that make more viruses. It’s a strange world when youstart looking under a microscope!1. What is a protozoan and how does it survive withonly one cell?2. Are all bacteria harmful?3. Is a virus alive or not?


7.1 ProtozoansImagine shrinking down to the size of a cell and going for a swim in a drop of pondwater (Figure 7.1). You enter a world filled with strange-looking creatures. Onepropels itself with a long whip. Another has hairs all over its body and uses them toswim. Watch out! There’s a blob coming toward you and he looks hungry! This worldmight sound strange but it’s real. Just look at a drop of water from a pond under amicroscope. The creatures described are single-celled organisms known asprotozoans. In this section, you will learn about their structure and function.What are protozoans?Protozoans aresingle-celledeukaryotesProtozoanhabitatsClassification ofprotozoansA protozoan (in Greek protos = first and zoon = animal) is asingle-celled eukaryote (an organism that has a cell nucleus)that has some animal-like characteristics. Many protozoans moveabout and feed like animals. Most protozoans exist as a single,eukaryotic cell. Some gather together in groups called colonies.Protozoans need a moist environment to survive. Ponds are idealhabitats for freshwater protozoans. They are also found in theocean, in moist soil, and in the cells and tissues of plants andanimals. In dry conditions, some protozoans can form a thick,protective wall around their cells. In this form, they can be blownabout by the wind just like dandelion seeds. When they come incontact with moist conditions, they return to their normal form.Protozoans are most often placed in the Kingdom Protista.This kingdom also includes the plant-like algae, and strangefungus-like organisms called slime molds. Algae live in aquaticenvironments and make their own food like plants (Figure 7.2).Slime molds grow in damp environments and absorb their food.Figure 7.1: What kind of life wouldyou encounter in a drop of pond water?protozoan - a single-celledeukaryote that has some animallikecharacteristics.Figure 7.2: Fucus is a type of algae.130UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLDStructure and function of protozoansProtozoans havespecializedorganellesCiliatesAmoebasProtozoans come in an amazing variety of forms even though theyconsist of a single cell. While animals and plants have specializedcells and tissues, protozoans have specialized organelles. Theseorganelles are used for movement, feeding, and other functions.Ciliates are a group of protozoans that move by waving tiny,hair-like organelles called cilia (Figure 7.3). A paramecium isan example of a ciliate. It waves its cilia like tiny oars to movethrough the water. It also uses its cilia to sweep food into anorganelle called a gullet. The contractile vacuole helps controlthe amount of water inside the paramecium. Since paramecia livein freshwater, there is a tendency for water to move into the cellby osmosis. The contractile vacuole pumps out excess water.Amoebas are protozoans that move by means of pseudopods (inLatin, “false feet.”) Amoeba proteus is a species found in ponds. Anamoeba stretches its cytoplasm in the direction it will move. Thestretched part becomes a pseudopod. The rest of the amoeba flowsinto the pseudopod. Amoebas also use their pseudopods to get food.An amoeba stretches out two pseudopods to surround a piece offood. The food is then taken in to form a food vacuole.Figure 7.3: A diagram of aparamecium.ciliates - a group of protozoansthat move by waving tiny, hair-likeorganelles called cilia.amoebas - a group of protozoansthat move by means ofpseudopods.7.1 PROTOZOANS131


FlagellatesThe euglena is acommonflagellateSporozoansFlagellates are a group of protozoans that move using a whip-likeorganelle called a flagella. Many flagellates are a combination ofplant and animal. They contain chlorophyll and can make theirown food, like a plant. But they also eat other things, like ananimal.A euglena is a flagellate commonly found in pond water(Figure 7.4). It has a flagella located at one end of its body. Itsmouth is located at the base of the flagella and leads to a gullet. Atthe same end, the euglena has a light-sensitive eyespot. Thiseyespot helps the euglena swim towards light so it can make itsown food. If the euglena is kept from sunlight for long periods oftime, its chlorophyll disappears and it loses the ability to make itsown food. Then, it survives on food that it takes from its habitat.Sporozoans are a group of protozoans that do not have organellesfor movement. All members of this group are parasites and live inthe bodies of animals. A parasite is an organism that lives in or onanother organism called a host. Parasites cause harm to theirhosts. Malaria is caused by a sporozoan called plasmodium.Malaria is transmitted by mosquitoes. When the mosquito bites,plasmodium gets into the blood and infects red blood cells. Infectedblood cells eventually burst causing sickness and death.Figure 7.4: A diagram of a euglena.flagellates - a group ofprotozoans that move using awhip-like organelle called aflagella.sporozoans - a group ofprotozoans that do not haveorganelles for movement andare parasites.parasite - an organism that livesin or on a host organism andcauses it harm.132UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLD7.1 Section Review1. To which kingdom do protozoans belong? What other organismsare in that kingdom?2. What are some animal-like characteristics of protozoans?Which characteristic of protozoans is not animal-like?3. What type of environment do protozoans need to survive?4. Label the parts of the organisms below:5. Complete the table below:Protozoan groupCiliatesAmoebasFlagellatesSporozoansType ofmovementflagellaOthercharacteristicsuse pseudopodsto get foodmany speciesare parasitesExampleparameciumEach group of protozoans (ciliates,amoebas, flagellates, andsporozoans) has parasitic species.Use the Internet and books to findat least one disease that affectshumans and is caused by amember of each group.Next, pick one of the diseases andmake an informational brochureabout it. Include the followinginformation in your brochure.1. What is the name and group ofthe organism that causes thedisease?2. How is the diseasetransmitted?3. What are the symptoms of thedisease?4. What parts of the world doesthe disease affect?5. What are the treatments for thedisease?6. How can the disease beprevented?7.1 PROTOZOANS133


7.2 Bacteria“Wash your hands—you don’t want to get sick from bacteria!” How many times haveyou heard a command like that? Bacteria are everywhere and some can make yousick. But did you know that many types of bacteria are helpful? In fact, life on Earthdepends on them. Bacteria take elements like carbon and nitrogen out of the air andturn them into compounds living things can use. They recycle nutrients from deadplants and animals so they can be reused. There are even bacteria in your digestivesystem (Figure 7.5)! In this section, you’ll learn about the structure and function ofbacterial cells.What are bacteria?Bacteria are theonly prokaryotesWhere dobacteria live?1 or 2 kingdomsof bacteria?Bacteria are organisms that consist of a single, prokaryotic cell.Bacteria are the only prokaryotes (cells with no nuclei). All otherlife forms on Earth are eukaryotes. Bacterial cells have a cellmembrane that is surrounded by a tough cell wall (Figure 7.6).Bacteria live on or in just about every material and environmenton Earth. They live in soil, water, and air. They are found in thecoldest regions of the Arctic and even in boiling waters nearundersea volcanoes. There are many bacteria in eachenvironment. A square centimeter of your skin has thousands ofbacteria. A teaspoon of soil contains more than a billion bacteria.Some scientists group all bacteria into the Kingdom Monera.Others divide bacteria into two kingdoms, Archaebacteria andEubacteria. Archaebacteria are found in extreme environmentslike volcanic vents in the ocean. They are thought to be the firstorganisms on Earth. Eubacteria are found almost everywhere elseand have a different chemical makeup than archaebacteria. Bothtypes of bacteria are prokaryotic, single-celled organisms. Asfuture discoveries are made, these groups may change.Figure 7.5: Bacteria in yourdigestive tract help you digest food.bacteria - organisms that consistof a single, prokaryotic cell.Bacterial cellCytoplasm Organelles notcovered bymembraneCell wallFigure 7.6: A bacterium is aprokaryotic cell.DNACellmembrane134UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLDSize and shape of bacteriaHow big arebacteria?Shapes ofbacterial cellsThe average bacterial cell is about 1.5 million times smaller thanthe average person. Bacteria are not easy to measure using meters,centimeters, or even millimeters. Micrometers (μm) are used tomeasure them. One micrometer is equal to one-millionth of ameter. The size of bacteria range from 1μm to 5μm. Eukaryotic cellstend to be about ten times larger than bacterial cells (Figure 7.7).Bacteria are often described according to the shape of their cells.Rod-shaped bacteria are called bacilli. Ball-shaped bacteria arecalled cocci. Spiral-shaped bacteria are called spirilla. Somebacterial cells exist as individuals while others exist in pairs,chains, or clusters. The graphic below shows the shapes of bacteria.Figure 7.7: Comparing the sizeof a typical bacteria to a typicaleukaryotic cell.Rod-shaped bacteria are called bacilli. Ballshapedbacteria are called cocci. Spiralshapedbacteria are called spirilla.Make a set of study flash cards tohelp you remember the terms youlearn in this chapter. Place theterm on one side of the card and itsdefinition on the other. Drawpictures along with the definitionwhere appropriate.7.2 BACTERIA135


Movement and feedingHow bacteriamoveSome bacteriamake theirown foodSome bacteriaget their foodfrom outsideBacteria move around in many ways. Some bacteria move usingflagella. They rotate their flagella to propel themselves throughliquid environments (Figure 7.8). Other bacteria have a slimylayer on the outside. They use it to slide over surfaces. Many typesof bacteria do not have their own means of movement. Bacteria aresimply carried by the movement of air or liquid. They can also betransferred from surface to surface. For example, when you toucha surface, bacteria are transferred from that surface to your skin.Bacteria get their food in manyways. Photosynthetic bacteriamake their own food fromsunlight and carbon dioxide,just like plants. Also likeplants, they produce oxygen.Cyanobacteria are examples ofphotosynthetic bacteria (right).Bacteria that live aroundvolcanic vents or other harshenvironments can make their own food without sunlight. They usechemicals to produce their food instead of energy from the sun.This process is called chemosynthesis.Many types of bacteria absorb food from the material they live onor in. Bacteria that break down dead organisms get their food inthis way. You have bacteria in your digestive system that absorbnutrients from the food you eat. Termites have bacteria in theirstomach that absorb and break down cellulose. Cellulose is thecompound that makes up wood, a termite’s favorite food. Thebacteria help the termite get energy and nutrients from wood.Figure 7.8: Some bacteria moveusing flagella.photosynthetic bacteria -bacteria that produce their ownfood through photosynthesis.136UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLDBacteria and the beginning of life on EarthBacteria were thefirst organismsBacteriaincreased oxygenin Earth’satmosphereScientists believe that bacteria were the first organisms on Earth.Evidence comes from fossils of single-celled prokaryotes found inrocks that are more than 3 billion years old. At that time, there waslittle oxygen in the atmosphere. The earliest life was thereforeanaerobic (Latin for “without oxygen”). Anaerobic bacteria do notrequire oxygen for cellular respiration. Today, anaerobic bacteriathrive in places that have little or no oxygen, like swamps.Over time, some bacteria developed the ability to usephotosynthesis. Cyanobacteria, still in existence today, wereone of the first photosynthetic bacteria. One of the products ofphotosynthesis is oxygen. Over hundreds of millions of years, theamount of oxygen in Earth’s atmosphere increased. This allowedaerobic bacteria to develop. Aerobic bacteria use oxygen forcellular respiration. There are many different species of aerobicbacteria living today.anaerobic bacteria - bacteriathat do not require oxygen tosurvive.aerobic bacteria - bacteria thatuse oxygen for cellular respiration.Eukaryotic cellsdeveloped fromprokaryotic cellsEventually, eukaryotic cells developed from bacteria. A scientifictheory states that long ago, smaller prokaryotic cells were engulfedby larger prokaryotic cells. The smaller cells began to survive byliving inside of the larger cells. Over time they took on specificfunctions inside the larger cells like producing energy. Eventually,the smaller cells became the organelles (like mitochondria) insideof eukaryotic cells (Figure 7.9).Figure 7.9: How eukaryotic cellsdeveloped from prokaryotic cells.7.2 BACTERIA137


The importance of bacteriaBacteria andindustrySymbiosisLife on Earthdepends onbacteriaBacteria andantibioticsBacteria are used in many areas of industry. Yogurt and cheeseare made with certain types of bacteria. Some important drugslike insulin are made with the help of bacteria. Sewage treatmentplants use bacteria to break down waste products. Other bacteriaare used in mining and to clean up oil spills. There is a goodchance that you’ve benefitted from bacteria today!Many kinds of bacteria have developed close relationships withother organisms. In many relationships the bacteria and theorganism it lives with benefit. We learned in Chapter 3 that thistype of symbiosis is called mutualism. One species of bacteria livesin your intestines. You provide the bacteria with a warm, safeplace to live. In return, the bacteria help you break down andabsorb certain compounds in foods. Bacteria even make somevitamins that your cells cannot make on their own.Bacteria are an important part of the nutrient cycles that all lifedepends upon. For example, plants need nitrogen to make aminoacids, the building blocks of protein. Bacteria in the soil takenitrogen out of the air and turn it into a form plants can use. Whenanimals eat plants, they rearrange the amino acids into otherproteins. When an organism dies, bacteria break down the deadmaterial and turn it back into compounds that living things canuse again (Figure 7.10). Bacteria are “nature’s recyclers.”Have you ever had a bacterial infection? If so, you’ve experiencedone of the harmful effects of bacteria. Bacteria cause diseases likestrep throat, respiratory infections, and infected wounds. Bacterialdiseases are treated with drugs called antibiotics. Antibiotics killbacteria without harming your own cells. Different antibiotics areused for fighting different types of bacteria.Figure 7.10: Bacteria are animportant part of nutrient cycles.138UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLD7.2 Section Review1. How are bacteria similar to and different from protozoans?2. Name the two major groups of bacteria.3. Which units are used to measure bacteria?4. Name each type of bacteria in the picture below.Scientists believe thatcyanobacteria were the firstphotosynthetic organisms. Explainhow this may have helped moreoxygen-breathing organisms todevelop.5. What is the difference between aerobic and anaerobic bacteria?6. Explain how bacteria changed Earth’s atmosphere.7. What is mutualism? Give one example of mutualism thatinvolves bacteria.8. List four important things about bacteria.9. How do plants depend on bacteria?10. Why are bacteria sometimes referred to as “nature’s recyclers?”11. What are antibiotics and how are they used?12. Beginning with ancient anaerobic bacteria, list the sequence ofsteps leading to the first eukaryotic cells.Bacteria reproduce rapidly.Suppose a population of bacteriadoubled every 24 hours. You startout with only 2 bacteria. Make apopulation vs. time graph. Usedays as your units of time andgraph the population from 0 to 14days.7.2 BACTERIA139


7.3 VirusesHave you ever had the flu? Your muscles ache and your throat is sore. You also get afever and an upset stomach. The flu is a disease caused by a virus. Viruses infectcells and cause many diseases, including smallpox, flu, AIDS, and the common cold.To infect means to invade and produce an infection. Viruses infect virtually all typesof cells: bacterium, protozoan, fungus, plant, animal, and human. In this section youwill learn about viruses and how they infect cells.The structure of virusesWhat is a virus?The structure ofvirusesA virus is a tiny, nonliving particle made up of genetic materialand protein. Viruses are not cells and are not made of cells. Byitself, a virus can do nothing. It does not eat, produce its own food,or reproduce. All a virus can do is wait for a host cell to infect. Ahost cell is a cell that is, or becomes, infected with a virus. Bothprokaryotic and eukaryotic cells can be hosts to viruses. Fluviruses may infect cells of your respiratory tract (Figure 7.11).When the virus spreads to many of your cells, you get sick.Viruses can be as much as 10,000 times smaller than bacteria. Avirus contains a core DNA.Surrounding that core is aprotein coat. In some viruses, theprotein coat is covered by anenvelope made of proteins, lipids,and carbohydrates. Thatenvelope may have spikes madeof carbohydrates and proteinsthat help the virus particlesattach to host cells.virus - a tiny, nonliving particlemade up of genetic material andprotein.host cell - a cell that is, orbecomes, infected with a virus.Figure 7.11: An image of flu virusesbursting out of a cell. The image wascaptured using an electron microscope.Photo courtesy CDC Public HealthImage Library.140UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLDHow viruses infect cellsHost cellsbecome factoriesfor the virusWhen some viruses come into contact with host cells, they triggerthe cells to engulf them. Other viruses fuse themselves to the cellmembrane and release their DNA into the cell. Once inside, theviral DNA changes the function of the cell. The cell now becomes afactory that produces new viruses. Eventually the infected cell diesand bursts, freeing the new viruses. In some cases, new viruses justpinch off so the cell remains alive.A tank crashes through the walls ofa car factory. People in the tankget out and turn the car factory intoa tank factory. An analogy is a wayto find similarities between thingsthat are different. How does thisanalogy explain how a virusreproduces? Try and think ofanother analogy for how a virusreproduces.Viruses andhost cellsA virus must be able to get its DNA inside of a cell before it canmultiply. The cell membrane controls what enters the cell. Howdoes a virus trick a cell into letting it enter? The “lock and key”mechanism is the most common explanation. Certain proteins onthe virus’ protein coat must fit certain receptor sites on the host’scell membrane (Figure 7.12). If the proteins fit, the virus can enterand infect the cell. If the proteins do not fit, the virus cannot enterthe cell or fuse with its cell membrane. Thus the viral DNA cannotenter the cell and cause an infection.Figure 7.12: If the proteins fit, thevirus can infect the cell.7.3 VIRUSES141


The spread of viruses and immunityThe spread of aviral infectionOnce free from the host cell, new viruses infect other cells.Because one virus causes a cell to produce thousands of newviruses, viral infections spread quickly throughout the body.Catching the flu is a good example of how this process works.The immunesystemAntibodies1. An infected person sneezes near you.2. You inhale a virus, and it attaches to cells lining the inside ofyour nose.3. The virus attacks those cells and causes them to make newviruses.4. The host cells break and new viruses spread into yourbloodstream and also into your lungs. Infected tissues causedifferent symptoms like muscle aches and sore throat.Your immune system protects your cells from unfamiliar objectslike viruses and bacteria (Figure ). With the flu virus, yourimmune system produces chemicals that cause your bodytemperature to increase. You get a fever. That fever slows downthe production of new viruses. This is because most of your body’schemical reactions work best at a temperature of 98.6 °F (37 °C). Ifyour temperature rises, the reactions slow down.Once the cells of your immune system recognizes a virus, theymake antibodies to stop further infections. Antibodies areproteins that bind to viruses and prevent them from infecting cells(Figure 7.13). If you come in contact with the same virus again,the cells of your immune system recognize it and immediatelystart producing antibodies to stop the virus’s spread. The cells ofyour immune system produce different antibodies for differentviruses.Figure 7.13: Antibodies preventviruses from entering cells.immune system - a system thatprotects an organism fromunfamiliar objects like viruses.antibodies - proteins that bind toviruses and prevent them frominfecting cells.142UNIT 2 CELL BIOLOGY


CHAPTER 7: THE MICROSCOPIC WORLDVaccinesChanges in theprotein coatA vaccine causes your immune system to produce antibodies to aparticular virus. A vaccine is a preparation made from weakenedvirus particles or their empty protein coats. That is why vaccines donot make you sick. Your immune system mounts a responseagainst the particles and makes antibodies. When you come incontact with the real virus, your immune system acts quickly toprevent illness (Figure 7.14).New vaccines must be made each year to prevent some viralinfections. The flu is a good example. After multiplying manytimes, flu viruses end up with mistakes in their geneticinstructions. These mistakes may alter the protein coat slightly.With a different protein coat, the immune system may notrecognize the virus. This means that one year’s batch of fluvaccines might not be as effective against the flu virus thenext year.7.3 Section Reviewvaccine - a preparation of virusparticles that, when injected intothe body, causes the immunesystem to produce antibodies.1. Why is a virus not considered a living thing?2. Explain using steps, how a virus multiplies.3. Name three diseases caused by a virus.4. Explain how a virus tricks a cell so it can enter it through thecell membrane.5. Describe, using several steps, how a virus infects cells andspreads throughout an organism.6. How does the immune system try to fight off a virus?7. What is a vaccine? Why do you think a vaccine is sometimesreferred to as “artificial immunity?”8. Explain why a new flu vaccine has to be produced each year. Figure 7.14: A vaccination helpsyour immune system produce antibodiesquickly when exposed to a virus.7.3 VIRUSES143


The Good, The Bad, The MicrobeChapter 7 ConnectionWhat are our bodies made of? Water, oxygen, tissue, yes -but you might be surprised to learn that living creatures alsomake up much of the human body. They are called microbesand billions of them are swirling inside you and on your skinright now. We cannot see or feel them, but microbes are allover us. And we can't live without them.What is a microbe?Microbes are singlecelledorganisms toosmall to see with thehuman eye. Scientistsuse microscopes tostudy them andunderstand how theywork. There are fourmajor types of microbes:bacteria, viruses, fungi,and protozoa.Microbes live all around us, in air and soil, in rocks andwater. They also live in plants, animals, and in our bodies.Microbes are the oldest life form on Earth. Scientistsestimate that these creatures date more than 3.5 billionyears.Microbiologists are scientists who study microbes. Theywork in a variety of settings: helping to keep our food andwater from contamination, working in hospitals to determinewhat germs make us sick, or trying to solve environmentalproblems.A friend and an enemyMicrobes are often called by the nickname “bugs.” Somemicrobes can cause sicknesses like the common cold, strepthroat, and chicken pox. However, more than 95 percent ofmicrobes are harmless, despite their bad reputation. Forexample, Escherichia coli (E. coli) lives safely in ourintestines. E. coli produces vitamins K and B-complex, twoessential nutrients we cannot make otherwise. We also havemany other useful bacteria living in our intestines thatprevent dangerous bacteria from infecting our bodies.Although most E. coli is helpful to our bodies, a rare straincauses severe food poisoning. It has a slightly differentgenetic makeup than the E. coli in our intestines. That otherstrain of E. coli is usually spread through contaminatedanimal meat, but can be killed easily by heat. All the morereason why the meat we eat be cooked to an internaltemperature of160° Fahrenheit.Bacteria play animportant role inproducing foodand medicine. Forexample, yogurt,sauerkraut, andcheese are allmade withbacteria.Streptomyces, abacteria found insoil, is used to makethe antibiotic streptomycin.144


Microbes can livein all kinds ofenvironments.Some requireoxygen, othersthrive without it.Also, microbes cansurvive along ahuge spectrum oftemperatures.Psychrophiles arecold-lovingbacteria that livein the Arctic and Antarctic at subfreezing temperatures. Ingreat contrast, thermophiles are heat-loving bacteria thatexist at extremely high temperatures. Thermophiles arefound in the hot springs of Yellowstone National Park, wheretemperatures are about 160°F. Extreme thermophiles, orhyperthermophiles, live near volcanic vents on the oceanfloor, where temperatures reach as high as 235°F.Bacteria of Searles LakeSearles Lake, located in the Mohave Desert of southeasternCalifornia, is also home to bacteria living in extremeconditions. In the summer, temperatures in this area reach100°F. The lake is about 10 times saltier and 70 times morealkaline than seawater. To make matters worse for livingcreatures, it has high concentrations of toxic elements likearsenic and boron. The arsenic levels are 29,000 timeshigher than that allowed in drinking water. Notsurprisingly, given such a harsh environment, very feworganisms live in Searles Lake. But scientists havediscovered bacteria that are able to survive. In fact, thesemicrobes use the dissolved arsenic as a source of energy. Bylearning more about them, scientists hope to find ways toclean drinking water that has been polluted by arsenic. Theyalso believe such knowledge may aid in their search for lifeon other planets.Questions:1. What are the four major types of microbes?2. What are the good and bad features associated withbacteria?3. What are some of the extreme environments in whichmicrobes can live?4. How do scientists hope to use what they learn from studyingthe bacteria of Searles Lake?Chapter 7 ConnectionUNIT 2 CELL BIOLOGY145


Chapter 7 ActivityOutbreak! Patient ZeroAn epidemic spreads rapidly by infection and affects manyindividuals in a population at the same time. Examples ofepidemics could be the flu, measles, and strep throat. Patientzero is the first patient in a population to become infected.Imagine that there is an outbreak of a bacterial infection atyour school. You know that the infection spreads throughphysical contact. Patient zero could have caught the bacteriaby touching an object that was infected. This person thenspread the bacteria by touching other items and individuals.In fact, you could be patient zero and don’t even know it! Inorder to contain the infection, you need to isolate its source.See if you can figure out the source of the infection in thefollowing simulation.For the activity, you will need a deck of cards.What you will do1. Shake hands with 3 different classmates hands andrecord the names of the students.2. Your teacher will randomly choose one card from the deckand NOT disclose its identity to the class. The card willthen be reinserted back into the deck.3. Each student will then select one card from the deck.4. The teacher will ask for all students who have the samecard number or face card to stand up. For example, allstudents holding the number 8 card. There can be up to 4students with the number 8 card. Or, all students with aKing. Again, there can be up to 4 students with a King.5. The students standing are the infected students. List thename or names on the board.6. Record the name of the student whom you suspect ispatient zero. Use evidence to support your hypothesis.7. Take a class poll to see who is the number one suspect.8. After you identify the student that is believe to be patientzero, make a flow chart as a class to see if your hypothesisis correct. Use the information from the hand-shakingactivity. If the flow chart does not work out, repeat theprocess until you are satisfied with the answer.Applying your knowledgea. Identify at least 2 ways that the outbreak activity isrealistic.b. You often come in contact with sick students but don'tbecome ill. What defenses does the human body have tofight off an infection?c. Are there any extra precautions that you and yourclassmates could have taken to reduce the spread of thedisease?d. Not all diseases are spread by physical contact. How elsemight diseases spread? List at least 2 other forms ofspreading a disease.146


Chapter 7 AssessmentVocabularySelect the correct term to complete the sentences.amoebas aerobic bacteriaanaerobic bacteriaantibodies bacteriaciliatesflagellates host cellimmune systemparasite photosynthetic bacteria protozoansporozoans vaccinationvirusSection 7.11. ____ move using tiny hair-like organelles.2. Ciliates, flagellates, amoebas, and sporozoans are the majorgroups of ____s.3. A ____ lives in or on a host organism and causes it harm.4. ____ include the Euglena, which is a common pond organismthat has characteristics of both plants and animals.5. The group of protozoans that have no organelles formovement are ____.6. ____ use their pseudopods for movement and feeding.Section 7.311. A ____ of an organism becomes infected with a virus.12. Your ____________________ protects you from unfamiliarobjects like bacteria and viruses.13. A ____________________ is not considered a living thingbecause it is not a cell and cannot eat, move, or reproducewithout a host.14. You get a ____ to teach your immune system to produce theantibodies to fight off viruses.15. Once your immune system recognizes a virus, it produces____ to stop further infections.ConceptsSection 7.11. What does the word “protozoan” mean?2. Name each labeled structure and explain its function.Section 7.27. Just like plants, ____ make their own food from sunlight andcarbon dioxide.8. Bacteria that use oxygen for cellular respiration are called____.9. Scientists believe that the first life on earth were ____because there was little oxygen in the atmosphere morethan 3 billion years ago.10. ____ are prokaryotes.CHAPTER 7 THE MICROSCOPIC WORLD147


3. What can some Protozoans do to survive through dryconditions?4. How are protozoans divided into major groups?5. Classify these Protozoan characteristics into the correctsubgroup:a. pseudopodsb. tiny oar-like hairsc. no special structure for movementd. whip-like tailSection 7.26. Compare and contrast prokaryotic and eukaryotic cells.7. Draw and a label a bacterial cell.8. Describe three different methods that bacteria have forlocomotion and nutrition.9. Explain four ways that bacteria are used in industry.10. The names of bacteria often give clues about their shape andarrangement. Read about these prefixes:• diplo - two• tetra - four• strepto - chain• staphylo - clumpsDraw what these bacteria would probably look like:a. tetracoccusb. diplobacillusc. streptobacillusd. staphylococcusSection 7.311. Create a chart to compare protozoans, bacteria, and virusesincluding these characteristics: cell type, size, structures,nutrition, locomotion, ways helpful, ways harmful.12. How do viruses trick cells so that it can enter?13. How do antibodies work to stop further infection?14. Why do scientists need to make new vaccinations each year?Math and Writing SkillsSection 7.11. Write a letter to a friend from the perspective of one of theseprotozoans: amoeba, paramecium, or euglena. Tell yourfriend about what you have been up to recently. Becreative.2. Create an acrostic for one of the groups or examples ofprotozoans. An acrostic is a series of lines in which certainletters, usually the first in each line, form a word or messagewhen read in order.Section 7.23. A bacterium divides once every half an hour. How manybacteria would there be after 3 hours?4. How large are eukaryotic cells? Remember that eukaryoticcells are 10 times larger than bacteria cells, which rangefrom 1 to 5 micrometers in length.5. Your friend thinks that the world would be a better placewithout bacteria. Convince him that bacteria are vital to lifeon Earth using at least three specific examples.148CHAPTER 7 THE MICROSCOPIC WORLD


CHAPTER 7 ASSESSMENTSection 7.36. If a virus was enlarged 10,000 times, it would be the size of agrain of salt. How tall would you be if you were enlarged10,000 times?7. How do you think computer viruses got their names?Compare and contrast computer viruses and viruses.8. Write a public service announcement for a radio show thatteaches young children how to stay healthy during cold andflu season.9. Interview your parents or family members to find out whatkind of vaccinations you have had and when you receivedthem.Only trueof bacteriaHow bacteriaand virusesare alikeHow all are alikeOnly trueof virusesChapter ProjectBacteria vs. VirusesBacteria and viruses are discussed daily on TV news reports, inthe newspapers, and in magazines. How are bacteria and virusesalike? How are they different? You could make lists ofcharacteristics, but a list isn't always helpful when you aretrying to learn concepts. A graphic organizer is a chart, diagram,or illustration that presents information in a visual way to helpyou understand ideas and concepts. For this project, create yourown graphic organizer to show how bacteria and viruses arealike and how they are different. Draw your graphic organizeron a computer or sketch it neatly on poster board. The blankorganizer to the right is a suggestion - you can use this idea orcome up with a graphic organizer of your own.How bacteriaandprotozoansare alikeOnly true of protozoansHow virusesandprotozoansare alikeUNIT 2 CELL BIOLOGY149

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