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- 1. © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 2Chapter 2 The Chemical Basis of Life
- 2. Figure 2.0_2 Chapter 2: Big Ideas Elements, Atoms, and Compounds Chemical Bonds Water’s Life- Supporting Properties
- 3. Introduction Chemicals are the stuff that make up – our bodies, – the bodies of other organisms, and – the physical environment. © 2012 Pearson Education, Inc.
- 4. Introduction Life’s chemistry is tied to water. – All living organisms require water. – The chemical reactions of your body occur in cells consisting of 70–95% water. © 2012 Pearson Education, Inc.
- 5. Living organisms are composed of matter, which is anything that occupies space and has mass (weight). – Matter is composed of chemical elements. – An element is a substance that cannot be broken down to other substances. – There are 92 elements in nature 2.1 Organisms are composed of elements, in combinations called compounds © 2012 Pearson Education, Inc.
- 6. A compound is a substance consisting of two or more different elements in a fixed ratio. Compounds are more common than pure elements. Sodium chloride, table salt, is a common compound of equal parts of sodium (Na) and chlorine (Cl). 2.1 © 2012 Pearson Education, Inc.
- 7. About 25 elements are essential to life. Four elements make up about 96% of the weight of most living organisms – oxygen, – carbon, – hydrogen, and – nitrogen. Trace elements are essential but are only needed in minute quantities. 2.1 © 2012 Pearson Education, Inc.
- 8. Table 2.1
- 9. 2.2 CONNECTION: Trace elements are common additives to food and water Some trace elements are required to prevent disease. – Without iron, your body cannot transport oxygen. – An iodine deficiency prevents production of thyroid hormones, resulting in goiter. © 2012 Pearson Education, Inc.
- 10. 2.2 CONNECTION: Trace elements are common additives to food and water Fluoride is added to municipal water and dental products to help reduce tooth decay. © 2012 Pearson Education, Inc.
- 11. 2.3 Atoms consist of protons, neutrons, and electrons The number of protons is the atom’s atomic number. © 2012 Pearson Education, Inc.
- 13. What are isotopes? Atoms of the same element with a different number of neutrons Why do isotopes of the same element have the same chemical properties?
- 14. 2.4 CONNECTION: Radioactive isotopes can help or harm us Radioactive tracers are frequently used in medical diagnosis. Sophisticated imaging instruments are used to detect them. – An imaging instrument that uses positron-emission tomography (PET) detects the location of injected radioactive materials. – PET is useful for diagnosing heart disorders, cancer, and in brain research. © 2012 Pearson Education, Inc.
- 15. Figure 2.4A
- 16. Figure 2.4B Healthy person Alzheimer’s patient
- 17. 2.4 CONNECTION: Radioactive isotopes can help or harm us In addition to benefits, there are also dangers associated with using radioactive substances. – Uncontrolled exposure can cause damage to some molecules in a living cell, especially DNA. – Chemical bonds are broken by the emitted energy, which causes abnormal bonds to form. © 2012 Pearson Education, Inc.
- 18. 2.5 The distribution of electrons determines an atom’s chemical properties Of the three subatomic particles—protons, neutrons, and electrons—only electrons are directly involved in chemical activity. Electrons occur in energy levels called electron shells. © 2012 Pearson Education, Inc.
- 19. Draw the electron configuration of the following elements: Calcium Oxygen
- 20. 2.5 Atoms with incomplete outer shells tend to react so that both atoms end up with completed outer shells. These atoms may react with each other by sharing, donating, or receiving electrons. These interactions usually result in atoms staying close together, held by attractions called chemical bonds. © 2012 Pearson Education, Inc.
- 21. 2.6 Covalent bonds join atoms into molecules through electron sharing The strongest kind of chemical bond is a covalent bond in which two atoms share one or more outer- shell electrons. Two or more atoms held together by covalent bonds form a molecule. – A covalent bond connects two hydrogen atoms in a molecule of the gas H2. Animation: Covalent Bonds © 2012 Pearson Education, Inc.
- 22. Table 2.6
- 23. 2.6 Water has atoms with different electronegativities. – Oxygen attracts the shared electrons more strongly than hydrogen. – So, the shared electrons spend more time near oxygen. – The oxygen atom has a slightly negative charge and the hydrogen atoms have a slightly positive charge. – The result is a polar covalent bond. – Because of these polar covalent bonds, water is a polar molecule. © 2012 Pearson Education, Inc.
- 24. Figure 2.6 (slightly +) (slightly −) (slightly +)
- 25. 2.7 Ionic bonds are attractions between ions of opposite charge An ion is an atom or molecule with an electrical charge resulting from gain or loss of electrons. – When an electron is lost, a positive charge results. – When an electron is gained, a negative charge results. Two ions with opposite charges attract each other. – When the attraction holds the ions together, it is called an ionic bond. – Salt is a synonym for an ionic compound. Animation: Ionic Bonds © 2012 Pearson Education, Inc.
- 26. Figure 2.7A_s2 Transfer of electron Na Sodium atom Cl Chlorine atom
- 27. Figure 2.7A_s2 Transfer of electron Na Sodium atom Cl Chlorine atom Na+ Sodium ion Cl− Chloride ion Sodium chloride (NaCl)
- 29. 2.8 Hydrogen bonds are weak bonds important in the chemistry of life Hydrogen, as part of a polar covalent bond, has a partial positive charge. The charged regions on molecules are electrically attracted to oppositely charged regions on neighboring molecules. Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond. Animation: Water Structure © 2012 Pearson Education, Inc.
- 31. 2.9 Chemical reactions make and break chemical bonds The formation of water from hydrogen and oxygen is an example of a chemical reaction. 2H2 + O2 2H2O The reactants (H2 and O2) are converted to H2O, the product. Chemical reactions do not create or destroy matter. Chemical reactions only rearrange matter. © 2012 Pearson Education, Inc.
- 32. Figure 2.9 Reactants Products 2 H2 O2 2 H2O
- 33. 2.10 Hydrogen bonds make liquid water cohesive The tendency of molecules of the same kind to stick together is cohesion. – Cohesion is much stronger for water than other liquids. – Most plants depend upon cohesion to help transport water and nutrients from their roots to their leaves. The tendency of two kinds of molecules to stick together is adhesion. © 2012 Pearson Education, Inc.
- 34. 2.10 Cohesion is related to surface tension—a measure of how difficult it is to break the surface of a liquid. – Hydrogen bonds give water high surface tension, making it behave as if it were coated with an invisible film. – Water striders stand on water without breaking the water surface. Animation: Water Transport © 2012 Pearson Education, Inc.
- 35. You should now be able to 1. Describe the importance of chemical elements to living organisms. 2. Explain the formation of compounds. 3. Describe the structure of an atom. 4. Distinguish between ionic, hydrogen, and covalent bonds. 5. Define a chemical reaction and explain how it changes the composition of matter. 6. List and define the life-supporting properties of water. 7. Explain the pH scale and the formation of acid and base solutions. © 2012 Pearson Education, Inc.
Notas do Editor
- Figure 2.0_2 Chapter 2: Big Ideas
- Biology is a multidisciplinary science, and concepts of both chemistry and physics apply.
- Biology is a multidisciplinary science, and concepts of both chemistry and physics apply.
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips The text notes the unique properties of pure sodium, pure chlorine, and the compound sodium chloride formed when the two bond together. Consider challenging your students to think of other simple examples of new properties that result when a compound is formed (for example, water, formed from hydrogen and oxygen, and rust, formed from iron and oxygen). Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet.
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips 1. The text notes the unique properties of pure sodium, pure chlorine, and the compound sodium chloride formed when the two bond together. Consider challenging your students to think of other simple examples of new properties that result when a compound is formed (for example, water, formed from hydrogen and oxygen, and rust, formed from iron and oxygen). 2. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet.
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips 1. The text notes the unique properties of pure sodium, pure chlorine, and the compound sodium chloride formed when the two bond together. Consider challenging your students to think of other simple examples of new properties that result when a compound is formed (for example, water, formed from hydrogen and oxygen, and rust, formed from iron and oxygen). 2. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet.
- Table 2.1 Elements In the Human Body
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet. 2. Many breakfast cereals are fortified with iron (see Figure 2.2c). As noted in Module 2.2, you can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imaging device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example.
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips 1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet. 2. Many breakfast cereals are fortified with iron (see Figure 2.2c). As noted in Module 2.2, you can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imaging device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example.
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Students with limited backgrounds in chemistry and physics might struggle with basic concepts of mass, weight, compounds, elements, and isotopes. It may also be early in the semester when mature study habits have not yet developed. Consider passing along basic studying advice and tips to help students master these early chemistry concepts. In-class quizzes (graded or not) or a few homework problems will also provide reinforcing practice. Teaching Tips Here is a comparison that helps make the point about the differences in mass of protons and electrons. If a proton were as massive as a bowling ball, an electron would be the mass of a Lifesaver. (This is calculated by considering a 15-pound bowling ball, a Lifesaver with a mass of 0.12 ounces, and the mention in Module 2.3 that an electron is about 1/2,000 the mass of a proton.) The text in Module 2.3 makes an analogy regarding the size of a helium atom. The text notes that if a helium atom were the size of a baseball stadium , the nucleus would be about the size of a fly in center field, and the two electrons would be like tiny gnats buzzing around the stadium. This analogy helps to relate the great distances between parts of an atom. Consider modifying the analogy to any local stadium in your region. Such concrete examples help to relate abstract concepts. Consider asking your students to compare the mass of the gnat orbiting a baseball stadium to the mass of the fly in center field. If a proton or neutron is about 2,000 times more massive than an electron, how does the mass of a helium nucleus compare to the mass of one of its electrons? The text notes the use of radioactive isotopes in dating fossils but references Module 15.5 for further discussion. If your course does not include Chapter 15, consider explaining this process at this point in your course.
- Figure 2.3B Model of a carbon atom
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Depending upon where you are teaching, radon in homes may be a common problem and significant health risk. If you are in a high radon region, consider adding details about home remediation methods and expenses or having students research the topic and report back.
- Figure 2.4A Technician monitoring the output of a PET scanner
- Figure 2.4B PET images of brains of a healthy person (left), and a person with Alzheimer’s disease (right)
- Student Misconceptions and Concerns The dangers posed by certain chemicals in our food and broader environment have sometimes misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why “natural” does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals. Teaching Tips The half-lives of many radioactive substances, especially those used for dating fossils, might lead some students to expect very long periods of decay for any radioactive substance. This might even be alarming if students are someday asked to consume a radioactive substance for a medical test. However, some medically significant isotopes have relatively short half-lives. Radioactive iodine-131 is often used to diagnose or treat certain thyroid problems. Its half-life of eight days means that it will decay quickly. Depending upon where you are teaching, radon in homes may be a common problem and significant health risk. If you are in a high radon region, consider adding details about home remediation methods and expenses or having students research the topic and report back.
- Teaching Tips Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example. Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
- Teaching Tips Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example. Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
- Student Misconceptions and Concerns Students with limited backgrounds in chemistry will benefit from a discussion of Table 2.6 and the differences and limitations of representing atomic structure. The contrast in Table 2.6 is a good beginning for such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as discussed in Module 2.3. Teaching Tips 1. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example. Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.) 2. Have your students try to calculate the number of covalent bonds possible for a variety of atoms. (Carbon, for example, can form up to four covalent bonds.) Then provide the students with a list of elements and the number of outer electrons for each and have them make predictions about the chemical formula for many types of molecules. (For example, carbon could form covalent bonds with four hydrogen atoms.) 3. Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
- Table 2.6 Alternative ways to represent four common molecules
- Student Misconceptions and Concerns Students with limited backgrounds in chemistry will benefit from a discussion of Table 2.6 and the differences and limitations of representing atomic structure. The contrast in Table 2.6 is a good beginning for such a discussion. In addition to comparing how the positions of electrons are depicted, note the problems with the sense of scale as discussed in Module 2.3. Teaching Tips Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example. Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.) Have your students try to calculate the number of covalent bonds possible for a variety of atoms. (Carbon, for example, can form up to four covalent bonds.) Then provide the students with a list of elements and the number of outer electrons for each and have them make predictions about the chemical formula for many types of molecules. (For example, carbon could form covalent bonds with four hydrogen atoms.) Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
- Figure 2.6 A water molecule, with polar covalent bonds
- Teaching Tips Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example.Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.)
- Figure 2.7A_s1 Formation of an ionic bond, producing sodium chloride (step 1)
- Figure 2.7A_s2 Formation of an ionic bond, producing sodium chloride (step 2)
- Figure 2.7B A crystal of sodium chloride
- Teaching Tips 1. Consider challenging your students to suggest relationships in human lives that are analogous to each of the three types of chemical bonds (covalent, ionic, and hydrogen). Evaluating the accuracy of potential analogies requires careful analysis of the chemical bonding relationships and practices critical thinking skills. Small groups might provide immediate critiques before passing along analogies for the entire class to consider. The following is one example. Ionic and covalent bonds are different types of relationships. Consider this analogy. A woman taking out a loan has a specific relationship to her bank. She owes the bank money, something she got from the bank. A man shares an office with another man. Both look out the same window and answer the same phone. Ionic bonds are like a bank loan, in which something is borrowed. Covalent bonds are like sharing an office, with items (electrons) shared by both members of the relationship. After presenting this analogy, ask your students to modify the office analogy to represent a polar covalent bond. (Perhaps one man in the office sits closer to the window and the phone.) 2. Modules 2.6 and 2.8 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
- Figure 2.8 Hydrogen bonds between water molecules
- Student Misconceptions and Concerns Students may misunderstand the chemical shorthand equation of photosynthesis presented in Module 2.9. As noted in the text, this overall equation does not include many smaller steps and reactions that occur in photosynthesis. If you discuss greater details of photosynthesis in your course, you might mention that you will address the details at a later time. A common student misconception is that energy is produced by a chemical reaction. When introducing chemical reactions, consider addressing the conservation of energy (the first law of thermodynamics) and the investment and release of energy in the creation and breaking of chemical bonds. Teaching Tips As noted in the text, chemical reactions do not create or destroy matter. Instead, they rearrange the structure and form new relationships. This is much like shuffling and dealing cards. When playing poker, cards are not created nor destroyed. Instead, new combinations are formed as the cards are dealt to the players. The overall reaction of photosynthesis illustrates the investment and release of energy by chemical reactions. Consider discussing the investment of sunlight energy to create chemical bonds and the release of energy in the form of heat when plant materials are burned. (Animals invest some of the energy released by the breakdown of sugars to form new chemical bonds, such as those in ATP.)
- Figure 2.9 Breaking and making of bonds in a chemical reaction
- Student Misconceptions and Concerns Students are unlikely to have carefully considered the four special properties of water that are apparent in our world. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for examples of each of these properties in each student’s experiences will require reflection and may produce meaningful illustrations. Similarly, quizzes or exam questions matching examples to a list of the properties may require high-level evaluative analysis. Teaching Tips 1. Here is a way to help your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? A towel helps us dry off water that is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water stick to each other. 2. Some students may be intrigued if you tell them that you too can stand on the surface of water— when it is frozen . Thus, it is necessary to note a liquid water surface when discussing surface tension.
- Student Misconceptions and Concerns Students are unlikely to have carefully considered the four special properties of water that are apparent in our world. However, these properties are of great biological significance and are often familiar parts of our lives. The connections between these properties and personal experiences can invest great meaning into a discussion of water’s properties. A homework assignment asking for examples of each of these properties in each student’s experiences will require reflection and may produce meaningful illustrations. Similarly, quizzes or exam questions matching examples to a list of the properties may require high-level evaluative analysis. Teaching Tips Here is a way to help your students think about the sticky nature of water in their lives. Ask them to consider the need for a towel after a shower or a bath. Once we get out of the shower or bath, we have left the source of water. So why do we need the towel? A towel helps us dry off water that is still clinging to our bodies because water molecules are polar. The molecules on cell surfaces are also polar, so our skin and the water stick to each other. Some students may be intrigued if you tell them that you too can stand on the surface of water— when it is frozen . Thus, it is necessary to note a liquid water surface when discussing surface tension.