The body and the face 2

“There’s No Such Thing as Sound Science” by By Christie Aschwanden was a lead science writer for FiveThirtyEight. FiveThirtyEight, Science, Dec. 6, 2017 Science is being turned against itself. For decades, its twin ideals of transparency and rigor have been weaponized by those who disagree with results produced by the scientific method. Under the Trump administration, that fight has ramped up again. In a move ostensibly meant to reduce conflicts of interest, Environmental Protection Agency Administrator Scott Pruitt has removed a number of scientists from advisory panels and replaced some of them with representatives from industries that the agency regulates. Like many in the Trump administration, Pruitt has also cast doubt on the reliability of climate science. For instance, in an interview with CNBC, Pruitt said that “measuring with precision human activity on the climate is something very challenging to do.” Similarly, Trump’s pick to head NASA, an agency that oversees a large portion the nation’s climate research, has insisted that research into human influence on climate lacks certainty, and he falsely claimed that “global temperatures stopped rising 10 years ago.” Kathleen Hartnett White, Trump’s nominee to head the White House Council on Environmental Quality, said in a Senate hearing last month that she thinks we “need to have more precise explanations of the human role and the natural role” in climate change. The same entreaties crop up again and again: We need to root out conflicts. We need more precise evidence. What makes these arguments so powerful is that they sound quite similar to the points raised by proponents of a very different call for change that’s coming from within science. This other movement strives to produce more robust, reproducible findings. Despite having dissimilar goals, the two forces espouse principles that look surprisingly alike: Science needs to be transparent. Results and methods should be openly shared so that outside researchers can independently reproduce and validate them. The methods used to collect and analyze data should be rigorous and clear, and conclusions must be supported by evidence. These are the arguments underlying an “open science” reform movement that was created, in part, as a response to a “reproducibility crisis” that has struck some fields of science.1 But they’re also used as talking points by politicians who are working to make it more difficult for the EPA and other federal agencies to use science in their regulatory decision-making, under the guise of basing policy on “sound science.” Science’s virtues are being wielded against it. What distinguishes the two calls for transparency is intent: Whereas the “open science” movement aims to make science more reliable, reproducible and robust, proponents of “sound science” have historically worked to amplify uncertainty, create doubt and undermine scientific discoveries that threaten their interests. “Our criticisms are founded in a confidence in science,” said Steven Goodman, co-director of the Meta-Research Innovation Center at Stanford and a proponent of open science. “That’s a fundamental difference — we’re critiquing science to make it better. Others are critiquing it to devalue the approach itself.” Calls to base public policy on “sound science” seem unassailable if you don’t know the term’s history. The phrase was adopted by the tobacco industry in the 1990s to counteract mounting evidence linking secondhand smoke to cancer. A 1992 Environmental Protection Agency report identified secondhand smoke as a human carcinogen, and Philip Morris responded by launching an initiative to promote what it called “sound science.” In an internal memo, Philip Morris vice president of corporate affairs Ellen Merlo wrote that the program was designed to “discredit the EPA report,” “prevent states and cities, as well as businesses from passing smoking bans” and “proactively” pass legislation to help their cause. The sound science tactic exploits a fundamental feature of the scientific process: Science does not produce absolute certainty. Contrary to how it’s sometimes represented to the public, science is not a magic wand that turns everything it touches to truth. Instead, it’s a process of uncertainty reduction, much like a game of 20 Questions. Any given study can rarely answer more than one question at a time, and each study usually raises a bunch of new questions in the process of answering old ones. “Science is a process rather than an answer,” said psychologist Alison Ledgerwood of the University of California, Davis. Every answer is provisional and subject to change in the face of new evidence. It’s not entirely correct to say that “this study proves this fact,” Ledgerwood said. “We should be talking instead about how science increases or decreases our confidence in something.” The tobacco industry’s brilliant tactic was to turn this baked-in uncertainty against the scientific enterprise itself. While insisting that they merely wanted to ensure that public policy was based on sound science, tobacco companies defined the term in a way that ensured that no science could ever be sound enough. The only sound science was certain science, which is an impossible standard to achieve. “Doubt is our product,” wrote one employee of the Brown & Williamson tobacco company in a 1969 internal memo. The note went on to say that doubt “is the best means of competing with the ‘body of fact’” and “establishing a controversy.” These strategies for undermining inconvenient science were so effective that they’ve served as a sort of playbook for industry interests ever since, said Stanford University science historian Robert Proctor. The sound science push is no longer just Philip Morris sowing doubt about the links between cigarettes and cancer. It’s also a 1998 action plan by the American Petroleum Institute, Chevron and Exxon Mobil to “install uncertainty” about the link between greenhouse gas emissions and climate change. It’s industry-funded groups’ late-1990s effort to question the science the EPA was using to set fine-particle-pollution air-quality standards that the industry didn’t want. And then there was the more recent effort by Dow Chemical to insist on more scientific certainty before banning a pesticide that the EPA’s scientists had deemed risky to children. Now comes a move by the Trump administration’s EPA to repeal a 2015 rule on wetlands protection by disregarding particular studies. (To name just a few examples.) Doubt merchants aren’t pushing for knowledge, they’re practicing what Proctor has dubbed “agnogenesis” — the intentional manufacture of ignorance. This ignorance isn’t simply the absence of knowing something; it’s a lack of comprehension deliberately created by agents who don’t want you to know, Proctor said.2 In the hands of doubt-makers, transparency becomes a rhetorical move. “It’s really difficult as a scientist or policy maker to make a stand against transparency and openness, because well, who would be against it?” said Karen Levy, researcher on information science at Cornell University. But at the same time, “you can couch everything in the language of transparency and it becomes a powerful weapon.” For instance, when the EPA was preparing to set new limits on particulate pollution in the 1990s, industry groups pushed back against the research and demanded access to primary data (including records that researchers had promised participants would remain confidential) and a reanalysis of the evidence. Their calls succeeded and a new analysis was performed. The reanalysis essentially confirmed the original conclusions, but the process of conducting it delayed the implementation of regulations and cost researchers time and money. Delay is a time-tested strategy. “Gridlock is the greatest friend a global warming skeptic has,” said Marc Morano, a prominent critic of global warming research and the executive director of ClimateDepot.com, in the documentary “Merchants of Doubt” (based on the book by the same name). Morano’s site is a project of the Committee for a Constructive Tomorrow, which has received funding from the oil and gas industry. “We’re the negative force. We’re just trying to stop stuff.” Some of these ploys are getting a fresh boost from Congress. The Data Quality Act (also known as the Information Quality Act) was reportedly written by an industry lobbyist and quietly passed as part of an appropriations bill in 2000. The rule mandates that federal agencies ensure the “quality, objectivity, utility, and integrity of information” that they disseminate, though it does little to define what these terms mean. The law also provides a mechanism for citizens and groups to challenge information that they deem inaccurate, including science that they disagree with. “It was passed in this very quiet way with no explicit debate about it — that should tell you a lot about the real goals,” Levy said. But what’s most telling about the Data Quality Act is how it’s been used, Levy said. A 2004 Washington Post analysis found that in the 20 months following its implementation, the act was repeatedly used by industry groups to push back against proposed regulations and bog down the decision-making process. Instead of deploying transparency as a fundamental principle that applies to all science, these interests have used transparency as a weapon to attack very particular findings that they would like to eradicate. Now Congress is considering another way to legislate how science is used. The Honest Act, a bill sponsored by Rep. Lamar Smith of Texas,3 is another example of what Levy calls a “Trojan horse” law that uses the language of transparency as a cover to achieve other political goals. Smith’s legislation would severely limit the kind of evidence the EPA could use for decision-making. Only studies whose raw data and computer codes were publicly available would be allowed for consideration. That might sound perfectly reasonable, and in many cases it is, Goodman said. But sometimes there are good reasons why researchers can’t conform to these rules, like when the data contains confidential or sensitive medical information.4 Critics, which include more than a dozen scientific organizations, argue that, in practice, the rules would prevent many studies from being considered in EPA reviews.5 It might seem like an easy task to sort good science from bad, but in reality it’s not so simple. “There’s a misplaced idea that we can definitively distinguish the good from the not-good science, but it’s all a matter of degree,” said Brian Nosek, executive director of the Center for Open Science. “There is no perfect study.” Requiring regulators to wait until they have (nonexistent) perfect evidence is essentially “a way of saying, ‘We don’t want to use evidence for our decision-making,’” Nosek said. Most scientific controversies aren’t about science at all, and once the sides are drawn, more data is unlikely to bring opponents into agreement. Michael Carolan, who researches the sociology of technology and scientific knowledge at Colorado State University, wrote in a 2008 paper about why objective knowledge is not enough to resolve environmental controversies. “While these controversies may appear on the surface to rest on disputed questions of fact, beneath often reside differing positions of value; values that can give shape to differing understandings of what ‘the facts’ are.” What’s needed in these cases isn’t more or better science, but mechanisms to bring those hidden values to the forefront of the discussion so that they can be debated transparently. “As long as we continue down this unabashedly naive road about what science is, and what it is capable of doing, we will continue to fail to reach any sort of meaningful consensus on these matters,” Carolan writes. The dispute over tobacco was never about the science of cigarettes’ link to cancer. It was about whether companies have the right to sell dangerous products and, if so, what obligations they have to the consumers who purchased them. Similarly, the debate over climate change isn’t about whether our planet is heating, but about how much responsibility each country and person bears for stopping it. While researching her book “Merchants of Doubt,” science historian Naomi Oreskes found that some of the same people who were defending the tobacco industry as scientific experts were also receiving industry money to deny the role of human activity in global warming. What these issues had in common, she realized, was that they all involved the need for government action. “None of this is about the science. All of this is a political debate about the role of government,” she said in the documentary. These controversies are really about values, not scientific facts, and acknowledging that would allow us to have more truthful and productive debates. What would that look like in practice? Instead of cherry-picking evidence to support a particular view (and insisting that the science points to a desired action), the various sides could lay out the values they are using to assess the evidence. For instance, in Europe, many decisions are guided by the precautionary principle — a system that values caution in the face of uncertainty and says that when the risks are unclear, it should be up to industries to show that their products and processes are not harmful, rather than requiring the government to prove that they are harmful before they can be regulated. By contrast, U.S. agencies tend to wait for strong evidence of harm before issuing regulations. Both approaches have critics, but the difference between them comes down to priorities: Is it better to exercise caution at the risk of burdening companies and perhaps the economy, or is it more important to avoid potential economic downsides even if it means that sometimes a harmful product or industrial process goes unregulated? In other words, under what circumstances do we agree to act on a risk? How certain do we need to be that the risk is real, and how many people would need to be at risk, and how costly is it to reduce that risk? Those are moral questions, not scientific ones, and openly discussing and identifying these kinds of judgment calls would lead to a more honest debate. Science matters, and we need to do it as rigorously as possible. But science can’t tell us how risky is too risky to allow products like cigarettes or potentially harmful pesticides to be sold — those are value judgements that only humans can make.

Improving one’s physical appearance is the primary concern, of all people from all walks of life. Not only the party goers, career-oriented, or the celebrities but also ordinary people like us. So one must be careful in choosing the kind of cosmetic products that will not cause any harmful effects to their health as well as the environment. Objectives: Pretest: Home Economics and Livelihood Education 7 Seibo College 43 Cosmetics are products used to beautify, clean or protect the skin, hair, and other parts of the body. Examples of these are make-up, gel, hair spray, and hair dye. Prolong usage of these products will be harmful for your health as well as the environment. What are cosmetics? Cosmetics refer to any preparation intended to beautify the human body, more specifically the face. Make-up preparations – are formulated with covering creams that are skin toned and dense in texture to hide or conceal skin blemishes. Hair spray - is a liquid preparation in an aerosol or other spray container use for holding the hair in place. Home Economics and Livelihood Education 7 Seibo College 44 Hair dye - is a hair coloring matter use to give hair a new color. Gel - a semi rigid or a dispersion of a solid with liquid as in jelly or glue, use to hold the hair in a specific style. Now, take note of the different components commonly found in hair spray. a. Aerosol – is a substance sealed in a container under pressure, with a device for releasing it as a fine spray. Components of aerosol: 1. propane gas - means colorless, flammable gas. 2. butane gas - is the most dangerous substance because it contains carcinogen 3. carcinogen - is a substance that causes cancer. Are you aware of the Global Warming? Do you feel the heat of the sun becoming more intense, especially during summer time? It is due to the continuous depletion of the Ozone Layer. And the depleted ozone layer is caused by aerosol, CFCs (chlorofluorocarbon) and air pollution. The presence of CFCs in the atmosphere can destroy millions of ozone molecules. The destruction of the ozone molecules can cause black hole on the ozone layer which allow the ultraviolet radiation to pass through it down to earth’s surface. Home Economics and Livelihood Education 7 Seibo College 45 Ultraviolet rays coming from the sun penetrates the earth causing us harmful effects. Exposure to the unabsorbed ultraviolet radiation can cause skin cancer. b. CFC - chlorofluorocarbon is a combination of the following components: 1. chlorine - it is a poisonous gas that is highly irritating to the respiratory organ. 2. Fluorine – a toxic gas that occurs with the combination of fluorite, enyolite and other minerals. 3. carbon atoms The above mentioned chemicals do not combine easily with other substances and only vaporize at low temperature. An excessive use may destroy the ozone layer which protects the earth from ultraviolet rays of the sun.

10 Multiple-Choice Questions About Wudu 1. What is the very first step you must perform before starting Wudu? A) Washing the hands to the wrists B) Having the intention (Niyyah) in the heart and saying "Bismillah" C) Rinsing the mouth D) Wiping the head Correct Answer: B 2. According to the Sunnah, how many times is it recommended to wash the hands, mouth, and nose? A) 1 time B) 2 times C) 3 times D) 4 times Correct Answer: C 3. What are the correct boundaries for washing the face during Wudu? A) From the forehead to the bridge of the nose, and from ear to ear B) From the normal hairline to the bottom of the chin, and from ear to ear C) Only the cheeks and the lips D) From the eyes to the neck, and from ear to ear Correct Answer: B 4. When washing your arms, where should the water start and where must it end? A) From the fingertips up to and including the elbows B) From the wrists to the shoulders C) From the elbows down to the wrists only D) From the palms to the forearms only Correct Answer: A 5. What is the correct way to wipe the head during Wudu? A) Wiping only the neck and back of the head B) Wiping the entire head with wet hands, from the front to the back and returning to the front C) Washing the head thoroughly with running water three times D) Wiping only the hair on the right side of the head Correct Answer: B 6. How should the ears be wiped, and do you need to take fresh water for them? A) They should be washed with running water three times B) They are wiped using the remaining wetness on the fingers after wiping the head, not with fresh water C) They should be wiped with fresh water using a towel D) Wiping the ears is optional and not part of the standard Wudu steps Correct Answer: B 7. Up to which part must the feet be washed completely during Wudu? A) Up to the toes only B) Up to and including the ankles C) Up to the mid-calf D) Only the bottom of the feet needs to be wiped Correct Answer: B 8. What does "Tartib" (Sequence) mean in Wudu? A) Washing the right limb before the left limb B) Performing the steps of Wudu in the specific order commanded by Allah and the Prophet C) Ensuring no parts of the body are left dry D) Repeating each step exactly three times Correct Answer: B 9. What does "Muwalat" (Continuity/Succession) mean during the ablution process? A) Washing each body part immediately after the previous one before it dries B) Using a large amount of water for each step C) Making sure to supplicate between every single step D) Taking a long break between washing the face and the arms Correct Answer: A 10. What is the recommended Supplication (Dua) to say immediately after completing Wudu? A) "Alhamdulillah" three times B) "Ash-hadu alla ilaha illallah wahdahu la sharika lah, wa ash-hadu anna Muhammadan 'abduhu wa Rasuluh" C) "Subhanallah" ten times D) Reading Surah Al-Fatiha Correct Answer: B

Personal cleanliness means attending to your personal hygiene regularly, thus keeping your body free from bad odor and infectious diseases. In keeping your body clean, you have to use grooming aids discussed in previous module. Remember that to achieve a clean and healthy body you need to practice good grooming habits as well as good healthy habits. Your Body Regular care of the body is necessary for good health and pleasing appearance. As you grow, you should learn to be responsible to your self. You should never neglect your body. Your body is the temple of the Holy Spirit. That is why , if you take good care of your body, you are in effect taking care of the place where the Holy Spirit resides. You are the “masterpiece of God’s creation” which means to say that you are above all other creations of God. So, it is best to maintain your body clean and healthy. For your own good and in so doing, you are showing your reverence to God, our creator. “Rule of Thumb” to keep your body clean is to take a regular bath. Taking a bath is necessary to remove dust, germs, as well as dirt accumulated from your daily activities. It is invigorating for the act of cleansing stimulates blood circulation. It will give your skin a healthy pinkish glow. Something to read: Home Economics and Livelihood Education 7 Seibo College 31 There are three ways of taking a bath: 1. Full bath It includes washing, shampooing the hair, soaping the whole body and rinsing with clear water. It is a thorough cleansing of the body. 2. Shower A shower bath usually takes a shorter time than full bath. A wash clothe or sponge with thick lather is rub all over the body starting from the navel, then the thigh, joints, armpits, and the rest of the body. Then rinse your body in the shower and pat your body dry with clean towel 3. Sponge bath Use wash cloth or face towel with soap, soak in warm or cold water. Rub it briskly over the body. Rinse the cloth with clean water then use it to remove soap from the body. A sponge bath is usually given to a sick person.

A solution is a mixture in which one or more substances are uniformly distributed in another substance. Solutions can be mixtures of liquids, solids, or gases. For example, plasma, the liquid part of blood, is a very complex solution. It is composed of many types of ions and large molecules, as well as gases, that are dissolved in water. A solute (SAHL-YOOT) is a substance dissolved in the solvent. The particles that compose a solute may be ions, atoms, or molecules. The solvent is the substance in which the solute is dissolved. For example, when sugar, a solute, and water, a solvent, are mixed, a solution of sugar water results. Though the sugar dissolves in the water, neither the sugar molecules nor the water molecules are altered chemically. If the water is boiled away, the sugar molecules remain and are unchanged. Solutions can be composed of various proportions of a given solute in a given solvent. Thus, solutions can vary in concentra- tion. The concentration of a solution is the amount of solute dis- solved in a fixed amount of the solution. For example, a 2 percent saltwater solution contains 2 g of salt dissolved in enough water to make 100 mL of solution. The more solute dissolved, the greater is the concentration of the solution. A saturated solution is one in which no more solute can dissolve. Aqueous (AY-kwee-uhs) solutions—solutions in which water is the solvent—are universally important to living things. Marine microorganisms spend their lives immersed in the sea, an aqueous solution. Most nutrients that plants need are in aqueous solutions in moist soil. Body cells exist in an aqueous solution of intercellu- lar fluid and are themselves filled with fluid; in fact, most chemical reactions that occur in the body occur in aqueous solutions. Copyright © by Holt, Rinehart and Winston. All rights reserved. Liquid water Solid water Ice (solid water) is less dense than liquid water because of the structure of ice crystals. The water molecules in ice are bonded to each other in a way that creates large amounts of open space between the molecules, relative to liquid water. FIGURE 2-12 solvent from the Latin solvere, meaning “to loosen” Word Roots and Origins CHEMISTRY OF LIFE 43 ACIDS AND BASES One of the most important aspects of a living system is the degree of its acidity or alkalinity. What do we mean when we use the terms acid and base? Ionization of Water As water molecules move about, they bump into one another. Some of these collisions are strong enough to result in a chemical change: one water molecule loses a proton (a hydrogen nucleus), and the other gains this proton. This reaction really occurs in two steps. First, one molecule of water pulls apart another water molecule, or dissociates, into two ions of opposite charge: H2O ∏ H OH The OH ion is known as the hydroxide ion. The free H ion can react with another water molecule, as shown in the equation below. H H2O ∏ H3O The H3O ion is known as the hydronium ion. Acidity or alkalin- ity is a measure of the relative amounts of hydronium ions and hydroxide ions dissolved in a solution. If the number of hydronium ions in a solution equals the number of hydroxide ions, the solution is said to be neutral. Pure water contains equal numbers of hydro- nium ions and hydroxide ions and is therefore a neutral solution. Acids If the number of hydronium ions in a solution is greater than the number of hydroxide ions, the solution is an acid. For example, when hydrogen chloride gas, HCl, is dissolved in water, its mol- ecules dissociate to form hydrogen ions, H, and chloride ions, Cl, as is shown in the equation below. HCl ∏ H Cl These free hydrogen ions combine with water molecules to form hydronium ions, H3O. This aqueous solution contains many more hydronium ions than it does hydroxide ions, making it an acidic solution. Acids tend to have a sour taste; how- ever, never taste a substance to test it for acidity. In concentrated forms, they are highly corrosive to some materials, as you can see in Figure 2-13. Bases If sodium hydroxide, NaOH, a solid, is dissolved in water, it dissociates to form sodium ions, Na, and hydroxide ions, OH, as shown in the equation below. NaOH ∏ Na OH Copyright © by Holt, Rinehart and Winston. All rights reserved. Eco Connection onnection Acid Precipitation Acid precipitation, more commonly called acid rain, describes rain, snow, sleet, or fog that contains high levels of sulfuric and nitric acids. These acids form when sulfur dioxide gas, SO2, and nitrogen oxide gas, NO, react with water in the atmosphere to produce sulfuric acid, H2SO4, and nitric acid, HNO3. Acid precipitation makes soil and bodies of water, such as lakes, more acidic than normal. These high acid levels can harm plant and animal life directly. A high level of acid in a lake may kill mollusks, fish, and amphibians. Even in a lake that does not have a very elevated level of acid, acid precipitation may leach aluminum and magnesium from soils, poisoning water- dwelling species. Reducing fossil-fuel consump- tion, such as occurs in gasoline engines and coal-burning power plants, should reduce high acid levels in precipitation. Sulfur dioxide, SO2, which is produced when fossil fuels are burned, reacts with water in the atmosphere to produce acid precipitation. Acid precipitation, or acid rain, can make lakes and rivers too acidic to support life and can even corrode stone, such as the face of this statue. FIGURE 2-13 44 CHAPTER 2 This solution then contains more hydroxide ions than hydronium ions and is therefore defined as a base. The adjective alkaline refers to bases. Bases have a bitter taste; however, never taste a substance to test for alkalinity. They tend to feel slippery because the OH ions react with the oil on our skin to form a soap. In fact, commercial soap is the product of a reaction between a base and a fat. pH Scientists have developed a scale for comparing the relative con- centrations of hydronium ions and hydroxide ions in a solution. This scale is called the pH scale, and it ranges from 0 to 14, as shown in Figure 2-14. A solution with a pH of 0 is very acidic, a solution with a pH of 7 is neutral, and a solution with a pH of 14 is very basic. A solution’s pH is measured on a logarithmic scale. That is, the change of one pH unit reflects a 10-fold change in the acidity or alkalinity. For example, urine has 10 times the H3O ions at a pH of 6 than water does at a pH of 7. Vinegar, has 1,000 times more H3O ions at a pH of 3 than urine at a pH of 6, and 10,000 times more H3O ions than water at a pH of 7. The pH of a solution can be measured with litmus paper or with some other chemical indicator that changes color at various pH levels. Buffers The control of pH is important for living systems. Enzymes can function only within a very narrow pH range. The control of pH in organisms is often accomplished with buffers. Buffers are chemi- cal substances that neutralize small amounts of either an acid or a base added to a solution. As Figure 2-14 shows, the composition of your internal environment—in terms of acidity and alkalinity— varies greatly. Some of your body fluids, such as stomach acid and urine, are acidic. Others, such as intestinal fluid and blood, are

Cells of different organisms and even cells within the same organism are very diverse in terms of shape, size, and internal organization. One theme that occurs again and again throughout biology is that form follows function. In other words, a cell’s function influences its physical features. Cell Shape The diversity in cell shapes reflects the different functions of cells. Compare the cell shapes shown in Figure 4-4. The long extensions that reach out in various directions from the nerve cell shown in Figure 4-4a allow the cell to send and receive nerve impulses. The flat, platelike shape of skin cells in Figure 4-4b suits their function of covering and protecting the surface of the body. As shown below, a cell’s shape can be simple or complex depending on the function of the cell. Each cell has a shape that has evolved to allow the cell to perform its function effectively. SECTION 2 OBJECTIVES ● Explain the relationship between cell shape and cell function. ● Identify the factor that limits cell size. ● Describe the three basic parts of a cell. ● Compare prokaryotic cells and eukaryotic cells. ● Analyze the relationship among cells, tissues, organs, organ systems, and organisms. VOCABULARY plasma membrane cytoplasm cytosol nucleus prokaryote eukaryote organelle tissue organ organ system Cells have various shapes. (a) Nerve cells have long extensions. (b) Skin cells are flat and platelike. (c) Egg cells are spherical. (d) Some bacteria are rod shaped. (e) Some plant cells are rectangular. FIGURE 4-4 (a) Nerve cell (b) Skin cells (c) Egg cell (d) Bacterial cells (e) Plant cells Copyright © by Holt, Rinehart and Winston. All rights reserved. 1. All cubes have volume and surface area. The total surface area is equal to the sum of the areas of each of the six sides (area = length X width). 2. If you split the first cube into eight smaller cubes, you get 48 sides. The volume remains constant, but the total surface area doubles. 3. If you split each of the eight cubes into eight smaller cubes, you have 64 cubes that together contain the same volume as the first cube. The total surface area, however, has doubled again. CELL STRUCTURE AND FUNCTION 73 Cell Size Cells differ not only in their shape but also in their size. A few types of cells are large enough to be seen by the unaided human eye. For example, the nerve cells that extend from a giraffe’s spinal cord to its foot can be 2 m (about 6 1/2 ft) long. A human egg cell is about the size of the period at the end of this sentence. Most cells, how- ever, are only 10 to 50 μm in diameter, or about 1/500 the size of the period at the end of this sentence. The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or its surface area–to-volume ratio. As a cell grows, its volume increases much faster than its surface area does, as shown in Figure 4-5. This trend is important because the materials needed by a cell (such as nutrients and oxygen) and the wastes produced by a cell (such as carbon dioxide) must pass into and out of the cell through its surface. If a cell were to become very large, the volume would increase much more than the surface area. Therefore, the surface area would not allow materials to enter or leave the cell quickly enough to meet the cell’s needs. As a result, most cells are microscopic in size. Comparing Surface Cells Materials microscope, prepared slides of plant (dicot) stem and ani- mal (human) skin, pencil, paper Procedure Examine slides by using medium magnification (100). Observe and draw the sur- face cells of the plant stem and the animal skin. Analysis How do the surface cells of each organism differ from the cells beneath the surface cells? What is the function of the surface cells? Explain how surface cells are suited to their function based on their shape. Quick Lab Small cells can exchange substances more readily than large cells because small objects have a higher surface area–to-volume ratio. FIGURE 4-5 mb06se_csfs02.qxd 5/18/07 10:54 AM Page 73 74 CHAPTER 4 BASIC PARTS OF A CELL Despite the diversity among cells, three basic features are common to all cell types. All cells have an outer boundary, an interior sub- stance, and a control region. Plasma Membrane The cell’s outer boundary, called the plasma membrane (or the cell membrane), covers a cell’s surface and acts as a barrier between the inside and the outside of a cell. All materials enter or exit through the plasma membrane. The surface of a plasma mem- brane is shown in Figure 4-6a. Cytoplasm The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not membrane-bound organelles is the cytosol. About 20 percent of the cytosol is made up of protein. Control Center Cells carry coded information in the form of DNA for regulating their functions and reproducing themselves. The DNA in some types of cells floats freely inside the cell. Other cells have a mem- brane-bound organelle that contains a cell’s DNA. This membrane- bound structure is called the nucleus. Most of the functions of a eukaryotic cell are controlled by the cell’s nucleus. The nucleus is often the most prominent structure within a eukaryotic cell. It maintains its shape with the help of a protein skeleton called the nuclear matrix. The nucleus of a typical animal cell is shown in

Lipids are large, nonpolar organic molecules. They do not dissolve in water. Lipids include triglycerides (trie-GLIS-uhr-IEDZ), phospho- lipids, steroids, waxes, and pigments. Lipid molecules have a higher ratio of carbon and hydrogen atoms to oxygen atoms than carbohydrates have. Because lipid molecules have larger numbers of carbon-hydrogen bonds per gram than other organic com- pounds do, they store more energy per gram. Fatty Acids Fatty acids are unbranched carbon chains that make up most lipids. Figure 3-10 shows that a fatty acid contains a long carbon chain (from 12 to 28 carbons) with a carboxyl group, —COOH, attached at one end. The two ends of the fatty-acid molecule have different properties. The carboxyl end is polar and is thus hydrophilic or attracted to water molecules. In contrast, the hydro- carbon end of the fatty-acid molecule is nonpolar. This end tends not to interact with water molecules and is said to be hydrophobic (HIE-droh-FOH-bik), or “water fearing.” In saturated fatty acids, such as palmitic acid, which is shown in Figure 3-10, each carbon atom is covalently bonded to four atoms. The carbon atoms are in effect full, or saturated. In contrast, linoleic acid, also shown in Figure 3-10, has carbon atoms that are not bonded to the maximum number of atoms to which they can bond. Instead, they have formed double bonds within the carbon chain. This type of fatty acid is said to be unsaturated. Triglycerides Three classes of lipids important to living things contain fatty acids: triglycerides (fats), phospholipids, and waxes. A triglyceride is composed of three molecules of fatty acid joined to one molecule of the alcohol glycerol. Saturated triglycerides are composed of saturated fatty acids. They typically have high melting points and tend to be hard at room temperature. Common dietary saturated triglycerides include butter and fats in red meat. In contrast, unsaturated triglycerides are composed of unsaturated fatty acids and are usually soft or liquid at room temperature. Unsaturated triglycerides are found primarily in plant seeds where they serve as an energy and carbon source for germinating plants. Phospholipids Phospholipids have two, rather than three, fatty acids attached to a molecule of glycerol. They have a phosphate group attached to the third carbon of the glycerol. As shown in Figure 3-11, the cell membrane is made of two layers of phospholipids, called the lipid bilayer. The inability of lipids to dissolve in water allows the mem- brane to form a barrier between the inside and outside of the cell. Hydrophilic “head” Phospholipids Hydrophobic “tail” Phospholipids Water Water The lipid bilayer of a cell membrane is a double row of phospholipids.The “tails” face each other.The “head” of a phospholipid, which contains a phosphate group, is polar and hydrophilic.The two tails are two fatty acids and are nonpolar and hydrophobic. FIGURE 3-11 H C H C O OH H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H C H H H H C H H C H H C H H C H H C H C O OH H C H H C H H C H C H C H C H H C H H C H C H H C H H C H C H H H H C H Fatty acids have a polar carboxyl head, highlighted in purple, and a nonpolar hydrocarbon tail, highlighted in green. FIGURE 3-10 Palmitic acid Linoleic acid mb06se_bchs02.qxd 5/18/07 10:49 AM Page 59 60 CHAPTER 3 1. Compare the structure of monosaccharides, dis- accharides, and polysaccharides. 2. How are proteins constructed from amino acids? 3. How do amino acids differ from one another? 4. Describe a model of enzyme action. 5. Why do phospholipids orient in a bilayer when in a watery environment, such as a cell? 6. Describe how the three major types of lipids differ in structure from one another. 7. What are the functions of the two types of nucleic acids? CRITICAL THINKING 8. Applying Information Before a long race, run- ners often “carbo load.” This means that they eat substantial quantities of carbohydrates. How might this help their performance? 9. Recognizing Relationships High temperatures can weaken bonds within a protein molecule. How might this explain the effects of using a hot curling iron or rollers in one’s hair? 10. Applying Information You want to eat more unsaturated than saturated fats. Name examples of foods you would eat more of and less of. SECTION 2 REVIEW Waxes A wax is a type of structural lipid consisting of a long fatty-acid chain joined to a long alcohol chain. Waxes are waterproof, and in plants, form a protective coating on the outer surfaces. Waxes also form protective layers in animals. For example, earwax helps pre- vent microorganisms from entering the ear canal. Steroids Unlike most other lipids, which are composed of fatty acids, steroid molecules are composed of four fused carbon rings with various functional groups attached to them. Many animal hor- mones, such as the male hormone testosterone, are steroid com- pounds. One of the most familiar steroids in humans is cholesterol. Cholesterol is needed by the body for nerve and other cells to func- tion normally. It is also a component of the cell membrane. NUCLEIC ACIDS Nucleic acids are very large and complex organic molecules that store and transfer important information in the cell. There are two major types of nucleic acids: deoxyribonucleic acid and ribonucleic acid. Deoxyribonucleic acid, or DNA, contains information that deter- mines the characteristics of an organism and directs its cell activi- ties. Ribonucleic (RIE-boh-noo-KLEE-ik) acid, or RNA, stores and transfers information from DNA that is essential for the manufactur- ing of proteins. Some RNA molecules can also act as enzymes. Both DNA and RNA are polymers, composed of thousands of linked monomers called nucleotides (NOO-klee-uh-TIEDS). As shown in Figure 3- 12, each nucleotide is made of three main components: a phosphate group, a five-carbon sugar, and a ring-shaped nitrogenous base.

When Europeans met American Indians in the late 15th century, the people of two continents exchanged many beneficial customs and goods. Europeans received New World crops such as potatoes and corn. American Indians acquired cloth and horses. However, besides the beneficial exchanges, Europeans and American Indians often traded deadly germs–bacteria and viruses–for which they had no immunity. Smallpox and Indians Image 1: Smallpox epidemics helped Europeans conquer the Aztec and Incan Empires of Mexico and South America. North American Indians quickly concluded that contact with Europeans often resulted in devastating diseases that caused widespread death. This drawing, made in the 1500s in Mexico, shows how the disease was passed from a European to an American Indian through simple contact. Many of the diseases that were common in Europe were entirely new to the peoples of North America. Diseases such as tuberculosis and measles could be fatal, but Europeans had developed resistance to the disease, so many people survived. However, when European diseases infected American Indians with no previous exposure, the people suffered terribly. The most devastating of these diseases was smallpox which is caused by a virus (Variola major). Smallpox, like many other diseases, had a latent period of about one week between the time the person was exposed to the disease and the time when signs of the disease became apparent. During this time, the sick person might begin a journey and carry the germs along with him. Anyone the person met would be exposed to smallpox. Anything the victim touched including clothing, bedding, or unwashed dishes carried living germs of smallpox. Cotton Mather Image 2: Cotton Mather was a Boston minister. When smallpox threatened Boston, he remembered reading about how the Turks inoculated people with dried material from smallpox blisters. The inoculation usually gave the person a mild case of the disease and future immunity. The procedure was highly controversial, but it helped save the lives of 274 people who were inoculated during the Boston smallpox epidemic of 1721. Symptoms of the disease began with fever, chills, and aches. The fever might raise a person’s temperature from the normal 98.6o to a dangerous 106o. After four days of misery, the victim entered the second stage when large pustules (fluid-filled bumps) appeared on the body. The rash made the person feel as if their skin were on fire. After suffering with the rash for nine days, the victim entered a new stage-if he or she had survived this long. The pustules opened and dried up. Each pustule formed a scab that turned into a scar that marked the person’s face for the rest of his or her life. Complications of smallpox for those who survived might include loss of vision or damage to the lungs, heart, or liver. Waterhouse Image 3: Dr. Benjamin Waterhouse of Harvard University brought Jenner’s smallpox preventative to the United States. It was called vaccination and used cowpox as the infective material. This much milder form of pox gave immunity to smallpox with fewer complications. Dr. Waterhouse encouraged President-elect Thomas Jefferson to promote vaccination. Jefferson responded, “Every friend of humanity must look with pleasure on this discovery, by which one evil more is withdrawn from the condition of man.” (T. Jefferson 12/25/1800 to Benjamin Waterhouse, December 25, 1800) Historians have found evidence of smallpox as far back as 1157 B.C. when the Egyptian pharaoh Ramses V apparently died of smallpox. From Egypt, where scientists believe smallpox began, the disease spread to Asia. Europeans began to experience periodic epidemics of smallpox in the14th century when Crusaders returning from the Middle East brought smallpox to Europe. People who survived the disease were immune and could not get smallpox again. This fact explains why epidemics struck periodically and the disease was not a constant threat to European societies. Smallpox Vaccination 1803 Image 4: Dr. Edward Jenner’s new smallpox vaccination (from cowpox) was widely accepted. This medical image was published by a Spanish physician to teach colonial doctors how to apply the vaccine to native Mexicans. The scratches were supposed to go through several stages of development as evidence that the vaccine had given the patient immunity. Vaccination was very effective in preventing smallpox epidemics among those who received the vaccine. In 1520, while Cortés was trying to conquer the Aztecs, smallpox broke out among the Spaniards and was transferred to the Aztecs. By 1527, the disease had migrated through Central America to Peru where it helped Pizarro conquer the Incas. (See Image 1.) In 1633, smallpox infected American Indians living near the English colony of Plymouth, Massachusetts. The disease traveled very quickly to tribes living far inland from the English colonies. In 1721, a smallpox epidemic threatened the English colonists of Boston. (See Image 2.) Cotton Mather, a Boston minister, wanted to inoculate people against the disease. He knew that Turkish healers took material from a dried smallpox scab and injected it into the body of a healthy person by scratching the surface of the skin. The patients developed a mild form of the disease from which they recovered. The procedure was highly controversial in Boston where about 280 Bostonians accepted inoculation. The epidemic infected more than half of the people living in Boston at the time. About 15% of those who got sick died of the disease. Among those who were inoculated, only six (2%) died of smallpox. The practice of inoculation spread to other English colonies, but not to the American Indian tribes living near the colonies. Late in the 18th century, British doctor Edward Jenner recognized that people who milked cows never came down with smallpox. They had already been infected with cowpox, a similar, but much milder disease that gave them immunity to smallpox. In 1796, Jenner inoculated a young man with cowpox virus he had collected from a milkmaid. The young man had a mild infection for less than 24 hours and recovered. Jenner’s efforts resulted in a widespread acceptance of vaccination (vaccine comes from Latin words meaning “taken from a cow”). By 1800, many Americans were receiving smallpox vaccinations. (See Image 3.) President Thomas Jefferson supported and encouraged the vaccination program in major American cities. (See Image 4.) By the middle of the 19th century, smallpox was under control, but broke out from time to time among unvaccinated people. Bismarck, Dakota Territory, experienced a small outbreak of smallpox in 1882. American Indians, however, were still subject to the disease in its most dangerous form.

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