SBI4U - Durham District School · PDF fileSBI4U – Biology Lesson 5 ... This transformation occurs during cellular respiration as the glucose molecules are broken down releasing not

SBI4U

Grade 12, University Preparation Biology

Unit 2 – Metabolic Processes

SBI4U – Biology Unit 2 - Introduction

Introduction In Unit 2, you will investigate the metabolic processes that relate to energy production in plant and animal cells and how those processes are related to one another. The basic ideas that were examined in SBI3U will be investigated in much greater detail. Human manipulation of these natural processes, both positive and negative, will augment your understanding of cellular metabolism and its implications in daily life. Overall Expectations After completing this unit, you will be able to: • analyse the role of metabolic processes in the functioning of biotic and abiotic

systems, and evaluate the importance of an understanding of these processes and related technologies to personal choices made in everyday life

• investigate the products of metabolic processes such as cellular respiration and photosynthesis

• demonstrate an understanding of the chemical changes and energy conversions that occur in metabolic processes

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SBI4U


Lesson 5 - Thermodynamics

SBI4U – Biology Lesson 5

Introduction One characteristic that separates living matter from non-living matter is the ability to manipulate the external environment. The most important of these is the manipulation of energy. For humans, this manipulation may be as basic as early man learning to control fire to create heat and light or as complicated as using nuclear or hydroelectric power to provide electricity for our homes. Whether the manipulation is simple or complicated, it involves one basic factor, converting a less useful form of energy into a more useful form. For us, these energy conversions make our lives easier, allowing us to convert electricity into the energy of motion (kinetic energy) when powering our hair dryers in the morning or converting electricity into heat to toast our bread for breakfast. But on a cellular, for all living things, a constant infusion of energy is required for development and maintenance. The source of this energy is the sun. Solar energy cannot be used directly by living things, but instead, must be converted into a usable form. Green plants initially trap the sun’s energy, and convert it into chemical energy which is stored in the bonds of organic molecules such as glucose. Plant eating animals or herbivores, then eat the plants and break down those organic molecules to release the energy to power their cells. Carnivorous animals then eat the herbivores and the cycle of energy capture, release and transformation continues. The metabolic processes that occur at the cellular level are responsible for extracting the energy from the chemical bonds of foods. In all of these situations, the energy conversions that occur are subject to the laws of thermodynamics, thermo – “heat” and dynamics – “change”. As such, the cellular metabolic processes are made more difficult by having to balance the release of energy with the resulting release of heat which could easily damage the cellular structure. Organisms have developed a complex series of metabolic pathways that allow the slow release of both. What You Will Learn After completing this lesson, you will be able to: • use the laws of thermodynamics to explain energy transfer in the cell during the

processes of cellular respiration and photosynthesis • use appropriate terminology related to the laws of thermodynamics including:

metabolism, entropy, enthalpy, endergonic, exergonic, endothermic, exothermic, free energy, bond energy



Thinking Activity and Questions Take a deck of ordinary playing cards and hold them in your hand. Bend them outwards until they spring free. Using a timer, determine how long it took you to pick them up versus how long it took them to fly out of your hand. Use the following questions to begin thinking about thermodynamics: • What type of energy did the cards make use of to fly from your hand? • Did it require more energy to order the cards back into a stack or to disorder them by

letting them fly free? • How does order and disorder relate to energy within the cell? Thermodynamics Thermodynamics deals with the transformations of energy in all its forms. Although the word literally means the “change of heat”, all forms of energy may be degraded to heat, so the rules that apply to heat transformations also apply to energy changes in general. Energy is the ability to do work. Work is defined as a force operating through a distance. Biologically, energy is used to courter-act the natural physical tendencies such as the diffusion of molecules down a concentration gradient. Energy exists in many forms. As stated earlier, some of these forms are more useful than others to living things. Heat is the energy associated with the rapid movement of molecules of matter. Mechanical energy is the energy found in the motion of objects. Chemical energy is the energy contained within the bonds that hold atoms together to form molecules. Radiant energy, the source of energy for all living things, is derived from the sun. All of these types of energy may be found in an actualized form such as the kinetic energy of a falling stone, or in potential form of a stone positioned at the top of a hill.

Figure 5-1 Kinetic and Potential Energy Source: Di Giuseppe et al. 59



The laws of thermodynamics govern all the transformations of energy in the natural world. The First Law of Thermodynamics The first law, also known as the law of conservation of energy, states that, “the total amount of energy in the universe is constant. Energy cannot be created nor destroyed, merely transferred or transformed”. This means that when an object or process gains energy, there is a loss of energy somewhere else in the universe. In the biotic, or living, environment, the radiant energy from the sun is transformed into chemical energy for storage within the organism in the process of photosynthesis. When energy is required to power various cellular functions, the stored chemical energy is again transformed into a form the cell can use called ATP, the primary energy-transferring compound. This transformation occurs during cellular respiration as the glucose molecules are broken down releasing not only the by-products of carbon dioxide and water but energy. In these scenarios, energy is being transferred and transformed from one type into another. But, no transformation is 100% efficient. Regardless of which type of transformation is taking place, some of the available energy is transformed into heat and therefore, some of the useful energy is lost. In living systems, the primary potential energy source is chemical energy. Organic molecules possess stability because of the bonds holding their atoms together in a particular arrangement. As discussed in the previous unit, covalent bonds with their full outer valence shells achieve stability. But, some bond arrangements are more stable than others. Bond energy is a measure of the stability of the covalent bond between atoms and is measured in kilojoules (kJ). It can be quantified as the amount of energy required to break one mole of bonds between two atoms and is also equal to the amount of energy released when that bond is formed. For example, the C – C bond requires 346 kJ/mol to break it apart whereas the C = O bond requires 799 kJ/mol which is almost twice as much. During chemical reactions, the reactant (starting) molecules must first be broken apart and then the product molecules must be formed. When energy or heat is applied to the reactant molecule, the bonds will absorb the energy until they weaken and then break apart. If a chemical reaction releases more heat than it uses, it is called an exothermic reaction, exo – “out”, thermic – “heat”. If more heat enters the system than is actually released at the end of the reaction, it is referred to as an endothermic reaction, endo – “in”, thermic – “heat”.



One of the most common and useful exothermic reactions in living organisms is combustion. The energy change that occurs is called the heat of combustion or ∆H. During this process, glucose is combined with oxygen releasing carbon dioxide and water. The overall equation for the combustion of glucose is:

C H O + 6O → 6CO + 6H O ∆H = kJ/mol C6H12O66 12 6 2 2 2 combustion

2870 kJ/mol

Figure 5-2 Endothermic and Exothermic Reactions Source: Di Giuseppe et al. 60

Support Questions

1. Describe three energy transformations that occur in everyday life.



The Second Law of Thermodynamics The second law focuses on the resulting consequences of energy transformations. During any transformation, energy tends to become increasingly unavailable for useful work. Since useful work is associated with producing order in the universe, this law can be expressed as a measure of the tendency for systems to move to states of increasing disorder or randomness. This disorder is known as entropy. Thus, the second law of thermodynamics states that, “the entropy of the universe increases with any change that occurs.” Thus, there is an unstoppable trend towards randomness. For example, if you stop cleaning your house, it quickly becomes disorganized. Much of the increasing entropy of the universe is less noticeable because it takes the form of an increasing amount of heat which it the energy of random molecular motion. Overall, when combining both the first and second laws of thermodynamics, it can be concluded that the quantity of energy in the universe remains constant but its quality is not. So, organisms use energy to decrease its entropy as the expense of creating an increase in entropy elsewhere in the universe.

Support Question

2. State the first and second laws of thermodynamics in common language. Free Energy During this lesson, we have talked about the energy that organisms use to power their cells. In terms of thermodynamics, this energy is referred to as free energy. This is the portion of a system’s energy that can perform work when the temperature is uniform throughout the system, as in a living cell. The quantity of free energy available in a system is symbolized by the letter G. There are two components to G; the system’s total energy (symbolized by H) and its entropy (symbolized by S). The free energy in a system can be represented by the equation, G = ∆H – TS T represents absolute temperature (in Kelvin units, equal to °C + 273). Notice that the temperature amplifies the entropy term of the equation. This is reasonable since temperature measures the intensity of random molecular motion or heat which tends to disrupt order. Overall, the equation shows not all of the energy stored in a system is available for work since some of that energy will be lost to more disordered and unusable forms such as heat.



Using this equation, one can predict what can and cannot occur in nature or specifically, in chemical reactions. Some events can occur spontaneously or without outside help while others cannot. For example, we know that water flows downhill. Water flowing downhill can be used to turn a turbine in a power plant so therefore, a spontaneous change can be harnessed to perform work. But, to move water uphill, an external source of energy must be added, such as a pump, to move the water against gravity. In living systems, the stability of a system increases when a spontaneous process occurs. Unstable systems tend to change to become more stable. Systems that are rich in energy such as complex molecules, are unstable. Thus, in a move towards stability, complex molecules will breakdown to form more stable products. Because the end product is more stable, free energy is released. This is called an exergonic (energy outward) reaction where ∆G is negative. Cellular respiration to break down glucose is a perfect example. For each mole of glucose broken down by respiration, 2870 kJ of energy are made available for work. Because energy must be conserved, the products of the reaction store 2870 kJ less than the reactants. But, before the complex organic molecules such as glucose can be broken down, they have to be formed. In this scenario, free energy must be absorbed from the surroundings. Because this type of reaction stores free energy, ∆G is positive and is referred to as an endergonic (energy inward) reaction. For the process of photosynthesis to create a mole glucose, 2870kJ of light energy must be absorbed from the sun by plants. In both cases, no matter the type of reaction that takes place, some level of energy must be added to the reaction in order to break apart the reactants. The amount of energy needed to strain and break the reactant’s bonds is called activation energy. When the activation energy is provided, the reactants will reach the transition state where the bonds within the reactants are breaking and the bonds of the products are forming. Thus, in living systems, the complementary processes of cellular respiration and photosynthesis are used as a means to capture, store and then release free energy to power the cell.

Support Questions

3. Explain the difference between endothermic versus endergonic and exothermic versus exergonic.

4. The free energy of a system is G = -1920 kJ/mol. Will the reaction occur

spontaneously? Is the reaction endergonic or exergonic?



The ATP Molecule As free energy is provided to the cell, it is used to do three main kinds of work. 1. mechanical work such as the contraction of muscle cells, the flow of cytoplasm or

the movement of chromosomes during cell reproduction 2. transport work such as the pumping of substances across membranes against

the concentration gradient 3. chemical work such as synthesizing complex molecules from simpler atoms The immediate source of energy that powers these cellular processes is ATP. ATP or adenosine triphosphate, is composed of the nitrogen base adenine bonded to the five-carbon sugar, ribose which is in turn bonded to three phosphate groups. The phosphate tail is unstable and the bonds between the last two phosphate groups can be broken. When the bond is broken, a molecule of inorganic phosphate is removed from ATP which then becomes ADP or adenosine diphosphate. Because the reaction is exergonic, energy is released which the cell can use. Once in its ADP form, the molecule can be “re-charged” to its higher energy state through the addition of another phosphate. This reaction is endergonic. Cellular respiration to breakdown glucose, as mentioned previously is a series of exergonic reactions that release the stored energy and drives the phosphorylation of ADP back into ATP. This molecule continually cycles through these two states, releasing energy as needed and then recharging.

Figure 5-3 The ATP Molecule Source: Campbell p. 96



Figure 5-4 The ATP/ADP Cycle Source: Blake et al. 55

Support Question

5. What is the role of ATP in energy transformations with living organisms? Key Question #5

1. Using the bond energies and the balanced equation provided, calculate the

∆Hcombustion of one mole of glucose. (11 marks)

Source: Di Giuseppe et al. Solutions p. 10



Bond Type Avg. bond energy (kJ/mol)

H – H 436 C – H 411 O – H 459 N – H 391 C – C 346 C – O 359 C = O 799 O = O 494

a. Determine the total bond energy for the reactants. (7 marks) b. Determine the total bond energy for the products. (3 marks) c. Calculate the difference between the two energy totals (the heat of

combustion. (1 mark) 2. Identify each of the following reactions as endergonic or exergonic. (4 marks)

a. Phosphorylating ADP into ATP b. burning gasoline c. breaking apart two molecules of glucose d. forming glucose from carbon dioxide and water

3. Jeremy comes home to a messy house. He begins to tidy up by sweeping the

floor, organizing his bookcase, making the bed and gathering his dirty clothes into a basket.

a. Has the entropy of the room increased or decreased due to these actions?

Explain. (2 marks) b. Has the entropy of the universe increased or decreased due to Jeremy’s

actions? Explain. (3 marks)


SBI4U


Lesson 6 – Photosynthesis


Introduction In the first lesson, you learned about the nature of energy and reactions that either require or release that energy. As was mentioned previously, plants are the first step in the energy capture process that allows sunlight or radiant energy to be transformed into chemical energy through the process of photosynthesis. In this lesson, you will examine this two part process in detail, looking at the structure of the organelle involved and the biochemical pathways that are able to convert water and carbon dioxide from the air into the organic molecule glucose with the help of the sun’s energy. What You Will Learn After completing this lesson, you will be able to: • use appropriate terminology including photolysis, Calvin cycle, light and dark

reactions, cyclic and non-cyclic phosphorylation • explain the chemical changes and energy conversions associated with the process

of photosynthesis • describe and illustrate the matter and energy transformations that occur during the

process of photosynthesis • describe the role of the chloroplast in photosynthesis Thought Questions Use the following questions to begin thinking about photosynthesis.

• Are all plant cells capable of photosynthesis? • How is sunlight energy captured and transformed? • What is the role of carbon dioxide and water in glucose formation? • Can photosynthesis only occur when light is present?

Photosynthesis Photosynthesis nourishes almost all living things directly or indirectly. The autotrophs or self-feeders are able to photosynthesize the important organic molecules from inorganic raw materials obtained from the environment. Plants and some algae are photoautotrophs, organisms that use light as a source of energy to synthesize carbohydrates, lipids, proteins and other organic substances. Heterotrophs obtain their organic material by eating plants and other animals. Thus, heterotrophs are completely dependent on photoautotrophs for food and also for oxygen, a by-product of photosynthesis. Although the basic chemical equation for photosynthesis seems relatively simple, the actual step-by-step pathways that convert the reactants to products is extremely detailed and complex.



In its simplest form, carbon dioxide from the atmosphere, along with water absorbed from the soil, interact using sunlight energy to produce glucose, oxygen and water and can be represented by the following word equation.

carbon dioxide + water + light energy → glucose + oxygen + water Using molecular formulas, we can summarize photosynthesis with the following chemical equation.

6 CO2 + 12 H2O + light energy → C6H12O6 + 6 O2 + 6 H2O Notice that in its true form, water is present on both sides of the equation. Even though 12 molecules of water are used, 6 molecules are actually produced. Therefore, the equation can be reduced even further to simply account for the consumption of water.

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 The Photosynthetic Structures In plant cells, photosynthesis occurs within the chloroplast. All the green parts of a plant, including the stems and unripened fruit, have chloroplasts, but the leaves are the major site of photosynthesis. There are approximately half a million chloroplasts per square millimetre of leaf surface. The majority of them are contained within the mesophyll cells which make up the interior of the leaf tissue. On the underside of the leaf are the stomata (pl.) which are microscopic pores that allow carbon dioxide to enter and oxygen to exit.

Figure 6-1 Cross Section of the Leaf Source: Di Giuseppe et al. 142 Chloroplasts have a double membrane, an outer and inner membrane. These membranes enclose an interior space filled with a semi-liquid material called stroma. A system of membrane-bound sacs called thylakoids is found within the stroma. They stack on top of one another to form columns called grana. These grana are sometimes



referred to as looking like a stack of pancakes. Adjacent grana are connected to one another by unstacked thylakoids called lamellae. Photosynthesis occurs partially within the stroma and partially within the thylakoid membrane which contains the light gathering pigment molecules and the electron transport chain responsible for generating ATP. This stacking of the photosynthetic structures allows for a greater surface area within the chloroplast which means more photosynthetic structures can be squeezed into the small amount of space. More structures equal more photosynthesis.

Figure 6-2 The Chloroplast Source: Di Giuseppe et al. 144 These are the structures involved in photosynthesis, but, the molecules that actually capture the sunlight energy are known as pigments. The main light-capturing pigments are the chlorophylls. The most important types are chlorophyll a and chlorophyll b. Both are structurally similar, consisting of a porphyrin ring, a central magnesium atom surrounded by a hydrocarbon ring with alternating single and double bonds, and a long hydrocarbon tail. The porphyrin ring contains electrons that absorb light energy and begin the photosynthetic process. The long hydrophobic tail is used to anchor the molecule within the membrane. Chlorophyll a and b differ in only one respect: chlorophyll a contains a methyl group (-CH3) while chlorophyll b contains an aldehyde group (-COH). This slight difference affects the type of light energy that the molecules can absorb.



Figure 6-3 The Chlorophyll Molecule Source: Di Giuseppe et al. 146 Pigments and Light Absorption When we talk about plants or the chloroplast absorbing light energy, we are talking about the range of energy or wavelengths given off by the sun that we call visible light. This is the light visible to the human eye. Although we see light as clear or white, it is actually composed of different wavelengths that we see as the colours of the rainbow, namely red, orange, yellow, green, blue, and purple or violet. Each of these colours travels through space, carrying a certain amount of energy. Some of these wavelengths are better absorbed by plants then others. Chlorophyll a, the most important of all the pigments, and chlorophyll b, absorb light in the blue-violet and red wavelengths (400-500 nm and 600-700 nm). The wavelength they actually absorb the least is in the green



range. This wavelength tends to pass through the plant or be reflected back. This is the reason we see the colour green. Rather than allow these other wavelengths to be wasted, plants carry accessory pigments in smaller amounts such as the carotenoids and xanthophylls. At the end of the growing season, once the chlorophyll molecules have broken down, it is the accessory pigments that create the yellow, orange and red leaf colours that we associate with fall. These pigments absorb wavelengths not used by chlorophyll. Although only chlorophyll a can absorb the energy needed to excite or activate the electrons, the other pigments are able to absorb energy at their own wavelengths and pass the activated electrons onto chlorophyll a. This allows the chloroplast to absorb the entire range of visible light. There combined absorption abilities can be expressed as an action spectrum.

Figure 6-4 The Absorption Spectrum of Chlorophyll Source: Di Giuseppe et al. 152

Support Question

1. In an experiment, a bean plant is illuminated with green light and another bean plant of similar size is illuminated with equally intense blue light. If all other conditions are controlled, how will the photosynthetic rates of the two plants most probably compare?



The Two Stages of Photosynthesis Although it is not evident in the chemical equation for photosynthesis, the process takes place in two distinct stages. The light-dependent stage is responsible for capturing the sunlight energy and converting it into chemical energy while the second stage, the light-independent stage, takes that chemical energy and produces glucose.

Figure 6-5 An Overview of Photosynthesis Source: Di Giuseppe et al. 147 Stage One: The Light-Dependent Stage 1. Photoexcitation of the Electrons In the functioning chloroplast, light is not absorbed by independent pigment molecules but rather, by molecules that are associated with proteins in clusters called photosystems. The photosystem contains a number of chlorophyll molecules and accessory pigments set in a protein matrix embedded in the thylakoid membrane. This structure is referred to as the antenna complex. The light-dependent reaction begins when a photon (unit of light energy) is absorbed by one of the molecules within the complex. Upon absorbing the photon, an electron gains energy and is raised to a higher potential energy level, called excitation. Prior to absorbing this energy, the electron is at its lowest possible energy level called the ground state. The electron is then moved from molecule to molecule until it reaches a specific chlorophyll a molecule called the primary electron acceptor. Depending upon the proteins associated with this chlorophyll a molecule, the basic photosystem can be one of two possible types. Photosystem I is also called P700 because its chlorophyll a molecule absorbs energy



most efficiently at 700 nm (red light). Photosystem II is called P680 because it absorbs light at 680 nm (red light). Regardless of which photosystem captures the electron, the energy stored within the electron can then be utilized to produce ATP and other high energy organic molecules through two possible electron pathways.

Figure 6-6 The Photosystem and Reaction Centre Source: Campbell p. 191 2. Cyclic Electron Pathway This electron pathway involves only the use of photosystem I to produce ATP. The pathway starts when a photon of light is absorbed and passed to the P700 chlorophyll a molecule. A high energy electron is ejected from the photosystem and passed to the electron acceptor ferredoxin, Fd, and from there, to a series of cytochrome molecules known as the b6-f complex. Along the way, as the electron is passed from acceptor to acceptor, it releases some of its energy which is used to phosphorylate ADP into ATP. Once the electron has reached a lower energy state, it moves back to the photosystem to be used again. Thus, in this system, the electrons cycle from a high energy state to a low energy state as they move from the photosystem to the acceptors and back again. This is the cyclical pathway. This process only produces ATP but, in order for glucose to be produced, another high energy molecule called NADPH (nicotinamide adenine dinucleotide phosphate) is also required.



Figure 6-7 The Cyclic Electron Pathway Source: Di Giuseppe et al. 160 3. Non-cyclic Electron Pathway This pathway involves both photosystems and creates both ATP and NADPH. Photosynthesis begins when a photon is absorbed by photosytem II and excites an electron of chlorophyll P680. The electron is then captured by the primary electron acceptor called pheophytin. It then goes through a series of redox reactions where it is passed along to the electron acceptor plastoquinone, PQ. Because this pathway is non-cyclical, the energized electron will not return to the photosystem and therefore, must be replaced. Once the electron leaves the photosystem, the Z enzyme uses light energy to split a water molecule into hydrogen ions and oxygen molecules. This process is called photolysis. The oxygen is released into the atmosphere while the liberated electron is captured by the photosystem. The Z enzyme also donates a hydrogen ion from the same water molecule to the P680 reaction center. The hydrogen ion will join the excited electron and travel with it from electron acceptor to acceptor. The excited electron and hydrogen ion pair move from plastoquinone to another b6-f cytochrome complex.



Figure 6-8 The Non-cyclic Electron Pathway Source: Di Giuseppe et al. 160 As the electron moves through the complex, the hydrogen ions are transported from the stroma into the thylakoid lumen. Other hydrogen ions are transported here by the cyclic electron pathway explained above to further increase the hydrogen ion concentration on this side of the membrane. The photolysis reaction by the Z enzyme also contributes hydrogen ions. This leads to the formation of a concentration gradient across the membrane. The movement of hydrogen ions back across the membrane releases energy that is used to phosphorylate ADP into ATP. This type of ATP formation is called chemiosmosis.



Figure 6-9 Chemiosmosis Source: Di Giuseppe et al. 158 The forgotten high energy electron that travelled with the hydrogen ion has, at this point, returned to its lower energy state. It is then transferred to the P700 molecule of photosystem I where it absorbs the energy from another incoming photon. It is passed to the electron acceptor ferredoxin and then to the enzyme NADP reductase which uses the electron and hydrogen ions from the stroma to reduce NADP+ to NADPH. Thus, between the two electron pathways, enough ATP has been generated to power the plant cells with enough left over to be shuttled along with NADPH to the light-independent stage of photosynthesis where glucose is produced. The relative rates of cyclic versus non-cyclic flow are regulated by the amount of NADPH available for use. If levels are high, cyclic flow will produce ATP while low levels stimulate non-cyclic flow.

Please visit the following website(s)

http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.htmlhttp://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swfhttp://www.sinauer.com/cooper/4e/animations1102.html


http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html

http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf

http://www.sinauer.com/cooper/4e/animations1102.html


Stage 2: The Light-Independent Stage (Calvin Cycle) In this portion of photosynthesis, the ATP molecules and the H+ ions stored in NADPH are used to reduce the carbon found in carbon dioxide to form sugar. The stage is sometimes mistakenly called the “dark reaction” which tends to suggest that it only occurs in the dark. Instead, it will occur both in the dark and in the light. It is not directly dependent on the presence of light but it does require the products of the light-dependent stage. As long as those products are present in sufficient quantities, the reaction will proceed. Unlike the light-dependent stage which takes place on the thylakoid membrane, this stage occurs in the stroma of the chloroplasts. The formation of the glucose sugar occurs in a series of cyclic reactions where some of the starting material is regenerated during the process. Every photosynthetic plant uses the Calvin cycle. It was named in honour of Melvin Calvin, the researcher who determined the steps involved in the process. The cycle itself, can be broken down into three distinct stages: carbon fixation, reduction and regeneration. 1. Carbon Fixation Initially, to incorporate carbon molecules into organic molecules, carbon dioxide brought into the plant cell through the stomata on the underside of the leaf, must first be attached to a 5-carbon compound called ribulose bisphosphate, RuBP which is already present in the stroma. The resulting 6-carbon molecule is highly unstable and is immediately split into two 3-carbon molecules of PGA or phosphoglycerate. Rubisco, a very large enzyme, catalyzes this reaction. This portion of the cycle must repeat three times before enough PGA molecules are generated to move onto the next stage. If three carbon dioxide molecules are fixed (1 C x 3 = 3C), they will join with three RuBP molecules (5 C x 3 = 15 C) and then split into 6 molecules of PGA (3 C x 6 = 18 C) which is the required amount. At this point, the 6 molecules can move onto the next step but this will only generate half of a glucose molecule. Therefore, in order to produce one full molecule of glucose, six carbon dioxide molecules need to enter the cycle so this portion of the pathway needs to be repeated six times in total. 2. Reduction of PGA In this phase, the six molecules of PGA are phosphorylated by six ATP molecules to form six higher energy molecules of 1,3-bisphosphoglycerate (1,3-BGP). The ATP molecules utilized in this step are the products of the light-dependent reaction. Next, six NADPH molecules, also produced in the light-dependent stage, donate a hydrogen ion and two electrons to 1,3-BGP reducing it to six molecules of glyceraldehyde-3-posphate (PGAL). The NADP+ is now free to return to the thylakoid membrane. One molecule of PGAL exits the cycle as a final product. It is capable of joining with other PGAL



molecules to form the various sugars made within the plant, including, most importantly, glucose. 3. RuBP Regeneration The five remaining PGAL (3 C x 5 = 15 C) molecules are rearranged with the help of three ATPs to regenerate three molecules of RuBP (5C x 3 = 15 C). This regeneration of RuBP allows more carbon dioxide molecules to enter the Calvin cycle and start the process all over again.

Figure 6-10 The Calvin Cycle






Support Questions

2. How many molecules of CO2 must enter the Calvin cycle for a plant to ultimately produce a sugar, such as sucrose, that contains 12 carbon atoms? How many ATP molecules will be used? How many NADPH molecules will be used?

3. Why do plants produce far more sugar than they need? Why do they not stop

photosynthesis once immediate needs are met? 4. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) blocks the

transport of electrons from photosystem II to the cytochrome b6-f complex. How will this affect the chloroplast’s ability to produce ATP? to produce NADPH?

Please visit the following website(s) to test your knowledge of photosynthesis.

http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_1/01Q.html http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_2/01Q.html

Key Question #6

1. Create a chart to distinguish between cyclic and non-cyclic electron flow in terms of: (4 x 2 marks = 8 marks) Yes and no answers can be used.

a. evolution of O2 b. production of NADPH c. production of ATP d. enabling the Calvin cycle to fix CO2

2. Explain the importance of each of the following to photosynthesis.

(7 x 2 marks = 14 marks)

a. H2O b. B6-f complex c. Rubisco d. Chlorophyll e. P680 f. Z enzyme g. PGAL


http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_1/01Q.html

http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_2/01Q.html


3. In an experiment, a team of researchers uses a heavy isotope of oxygen-18 to track the passage of oxygen through the process of photosynthesis. What results would you expect to find if the researchers initiated the reaction in which

a. the carbon dioxide contained the heavy oxygen (2 marks) b. the water contained the heavy oxygen (2 marks)


SBI4U


Lesson 7 – Cellular Respiration


Introduction In the previous lesson, you learned how plants are able to convert sunlight energy into chemical energy and store the excess in the form of glucose. Animals or heterotrophs, are unable to make their own food so must either directly or indirectly eat plants to gain a form of energy that they can utilize. Once glucose enters the system, cellular processes are in place to break down the sugar molecule and release the stored energy. Because this process is exergonic, it must be accomplished in a series of steps to reduce the subsequent heat release which could damage the cell. Small, usually unicellular organisms, are able to use the anaerobic or oxygen free process called fermentation to satisfy their energy needs. Large multi-cellular organisms have much larger energy requirements and need to release additional stored energy to survive. These organisms use the three part process known as cellular respiration to generate this energy. What You Will Learn After completing this lesson, you will be able to: • Use appropriate terminology including glycolysis, Krebs cycle, electron transport

chain, oxidative phosphorylation, substrate level phosphorylation, alcohol fermentation, lactic acid fermentation and ATP synthase

• Explain the chemical changes and energy conversions associated with the processes of aerobic and anaerobic cellular respiration

Activity and Thought Questions Materials: clothespin and timer Hold a clothespin in the thumb and index finger of your dominant hand. Using the timer, time how long you are able to open and close the clothespin as completely and as quickly as possible. Once you can no longer attempt the activity (if the activity is done properly, your fingers won’t be able to close anymore) try it again with your non-dominant hand. 1. How long does it take for your dominant hand to fatigue? your non-dominant

hand? 2. How do your fingers feel at the end of the activity? 3. Why do your fingers stop working?



Cellular Respiration We have all seen the advertisements for energy drinks that claim they can put pep in your step when your energy levels are low. The majority of them contain high levels of caffeine but if you read the label, they also contain massive quantities of sugar. It is the sugars that your body is able to break down quickly to produce more cellular energy. Cells have developed a number of different mechanisms to extract the energy they need from available nutrients. Organisms are able to break the covalent bonds of the glucose molecule and through a series of redox reactions, rearrange the sugar molecule into new and more stable configurations. During cellular respiration, the redox reactions result in the transfer of electrons from glucose to oxygen. The glucose is oxidized to carbon dioxide and the oxygen is reduced to water. The overall chemical equation is as follows:

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy as heat and ATP This equation is merely a summary of the process. In reality, the anaerobic portion of the process combined with the aerobic portion translates to a series of approximately 30 enzyme controlled steps. The large number of steps is necessary to dissipate the heat that is released from the reaction. The body’s “burning” of glucose is no different than burning gasoline to run your car or burning propane to heat your barbeque. When glucose is broken down, the liberated free energy, about -2870 kJ/mol of it, can be converted to ATP which the cell can readily use to power all of its endergonic processes. Overall, cellular respiration can be broken down into three main stages: A. glycolysis- the anaerobic (absence of oxygen) stage where a small amount of

ATP is produced along with the molecule pyruvate which moves on to the next part of the process

B. pyruvate oxidation and the Krebs cycle- this begins the aerobic portion where the

pyruvate molecule is first altered and then enters a cyclical pathway which generates some ATP along with the high energy molecules of NADH

C. electron transport chain and chemiosmosis- the high energy NADH molecules

are used to generate ATP in a process called oxidative phosphorylation



Figure 7-1 An Overview of Cellular Respiration Source: Di Giuseppe et al. 94 The Organelle of Cellular Respiration: The Mitochondrian Unlike photosynthesis which takes place completely within the chloroplast, cellular respiration occurs partially within the cytoplasm and partially within the mitochondrian. The mitochondrian itself, is an oval like structure composed of an outer membrane and a highly folded inner membrane. The inner folded portions of the membrane are referred to as cristae and create a much larger surface area. This allows more of the numerous proteins and enzymes associated with the later stages of cellular respiration, to be present. As well, the inner membrane creates two compartments within the mitochondrian. The inner most space of the mitochondrian, called the mitochondrial matrix, contains a protein rich liquid. The intermembrane space which is found between the inner and outer membrane, is also fluid filled. Both compartments play an important role in cellular respiration.

Figure 7-2 The Mitochondrian Source: Di Giuseppe et al. 100



Support Question

1. Arrange the following types of cells in order of increasing number of mitochondria

in the cytoplasm: nerve cell, skin cell, fat cell, heart muscle cell. Provide an explanation for your sequence.

Stage One: Glycolysis This first stage of cellular respiration takes place in the cytoplasm of the cell. It is an anaerobic process meaning that oxygen is not required. Its goal is to split the six carbon glucose molecule into two 3-carbon pyruvate molecules. The term glycolysis literally means “sugar-splitting”. The process is accomplished in a series of ten steps each involving a different enzyme. The first five steps are the energy investment phase where the cell uses up ATP. The last five steps are the energy payoff phase where ATP is produced by a process called substrate-level phosphorylation. In this type of ATP production, ATP is formed directly when a phosphate-containing compound transfers a phosphate to ADP forming ATP. At the end of the ten steps, two ATP molecules, two NADH molecules and two pyruvate molecules have been created. Right in the very first step, an ATP is used up as its terminal phosphate is transferred to carbon six of the glucose molecule. The molecule is then rearranged to form an isomer and another ATP is used transferring its phosphate to carbon one. At this point, the fructose 1,6-bisphosphate molecule is split into one molecule of glyceraldehyde-3-phosphate (G3P) and one molecule of dihydroxyacetone phosphate (DHAP). Since only G3P can continue through the rest of the reactions, DHAP which is an isomer, is converted into a second molecule of G3P. From this point on, two molecules will continue through the rest of the steps effectively doubling the products created. This is the energy investment portion of the process where two ATP molecules have been used. The G3P sugar is then oxidized by the transfer of electrons and a proton to the carrier molecule NAD+ (nicotinamide adenine dinucleotide) to create NADH. Because this oxidation is an exergonic process, the energy that is released is used to attach an inorganic phosphate from the cytoplasm to carbon one. We now have a molecule with two attached phosphates and substrate-level phosphorylation can now be used to create ATP. Remember that two molecules are moving through these steps so this step produces a total of 2 ATPs. Since 2 ATPs were used up in the first part of the process, the ATP ledger now stands at zero. The remaining phosphate group is then transferred to another part of the molecule and a molecule of water is removed creating a double bond. This leads to the rearrangement of some of the electrons which causes the remaining phosphate group to become unstable. Substrate-level phosphorylation occurs again, generating another 2 ATPs. The resulting formation of pyruvate ends this first anaerobic stage of cellular respiration.



Figure 7-3 Glycolysis Source: Di Giuseppe et al. 98


http://trc.ucdavis.edu/biosci10v/bis10v/media/ch06/glycolysis.swfhttp://www.terravivida.com/vivida/glysteps/step02c.htmhttp://www.sinauer.com/cooper/4e/animations0303.html


http://trc.ucdavis.edu/biosci10v/bis10v/media/ch06/glycolysis.swf

http://www.terravivida.com/vivida/glysteps/step02c.htm



Support Questions

2. What would happen to an organism that lacked the enzyme that catalyzes the first step in glycolysis?

3. Which stores more potential energy: one molecule of glucose or two molecules of

pyruvate? Explain. Stage 2: Pyruvate Oxidation and the Krebs Cycle The pyruvate molecules that are formed are able to enter the mitochondrian for the next stage of cellular respiration. Pyruvate’s carboxyl group contains very little energy and as such, is removed and released as CO2. The remaining two carbon fragment is oxidized to form the compound acetate. An enzyme transfers the extracted electrons to NAD+, storing energy in the form of NADH. Finally, coenzyme A, a sulphur-containing compound derived from a B vitamin, is attached to the acetate by an unstable bond that makes the acetyl group very reactive. It is the resulting acetyl CoA product of this reaction that enters the Krebs cycle for further oxidation.

Figure 7-4 Pyruvate Oxidation Source: Blake et al. 70 The overall goal of the Krebs cycle or citric acid cycle as it is also known, is to rearrange the carbon molecule that forms in order to remove electrons and store the energy in NADH molecules. Because two molecules of acetyl CoA are formed from one molecule of glucose, the Krebs cycle occurs twice for every glucose molecule processed. Each acetyl CoA molecule attaches itself to the 4-carbon oxaloacetate. The resulting 6-carbon citrate



molecule is rearranged and a carbon is removed and released as CO2. The 5-carbon alpha-ketogluterate is oxidized, reducing NAD+ to NADH and another carbon is removed and released as CO2. The 4-carbon compound is then attached to a CoA enzyme similar to the one involved in oxidizing pyruvate. The unstable bond that forms allows for substrate-level phosphorylation to occur where CoA is displaced by a phosphate group which is then transferred to a GDP (guanosine diphosphate) to form GTP (guanosine triphosphate). GTP is similar to ATP which then forms as GTP transfers its phosphate to an ADP molecule. The resulting 4-carbon succinate molecule is rearranged and the resulting energy leads to a redox reaction involving another energy carrier molecule FAD (flavin adenine dinucleotide). FADH2 is produced. Not enough energy is liberated to reduce NAD+ so this second lower energy carrier is used. The 4-carbon molecule is rearranged further until oxaloacetate is reformed and ready to pick up the next acetyl CoA molecule that enters the cycle. This last conversion also releases enough energy to create another NADH. In total, this two step stage produces 2 ATP molecules, 8 NADH molecules and 2 FADH2 molecules. Remember, the cycle occurs twice for one molecule of glucose.


http://highered.mcgraw-hill.com/sites/dl/free/0072507470/291136/krebsCycle.swf http://www.sinauer.com/cooper/4e/animations0304.html


http://highered.mcgraw-hill.com/sites/dl/free/0072507470/291136/krebsCycle.swf



Figure 7-5 The Krebs or Citric Acid Cycle Source: Blake et al. 71



Stage 3: The Electron Transport Chain (ETC) and Oxidative Phosphorylation In this third phase of cellular respiration, electrons harvested from the oxidation of glucose in the previous phases are transferred to the inner mitochondrial membrane by the energy carrier molecules NADH and FADH2. A series of enzymes that act as electron acceptors move the electrons through the electron transport chain embedded in the membrane. As the electrons are passed to the first electron acceptor, FMN or flavin mononucleotide, the protons that accompanied the electrons, hitch a ride and end up in the innermembrane space (IMS). As the electrons get passed from acceptor to acceptor, protons are able to move into the IMS such that every electron pair moves six protons from the matrix side into the IMS. The concentrating of the protons in the IMS creates two gradients across the membrane: a concentration gradient of protons and an electrostatic gradient of potential energy versus ATP. This is called the proton motive force or PMF. It is the potential energy generated across the membrane that provides the energy for the formation of ATP. As the protons move back across the membrane through special channels, the enzyme ATP synthase is activated. The energy release is used by the enzyme to phosphorylate ADP into ATP. This is oxidative phosphorylation. In terms of ATP generation, every NADH molecule from the Krebs cycle produces 3 ATP molecules. Every NADH molecule generated during glycolysis and the FADH2 from the Krebs cycle are able to generate 2 ATP molecules. Once the electrons have moved through the electron acceptors, they reach the final electron acceptor which is oxygen. The oxygen atom combines with the electrons and a proton from the surrounding fluid to form water which is released from the cell. It is the job of oxygen to siphon off the electrons from the end of the chain so that they do not clog up the pathway. This is why we breathe in oxygen, to remove the electrons from the electron transport chain. If not enough oxygen is available to pick up the electrons, the pathway will eventually become backed up and shut down, effectively stopping ATP production. In desperation, the body will turn to lactic acid fermentation as a means of creating energy when oxygen is not available.


http://highered.mcgraw-hill.com/sites/dl/free/0072507470/291136/electon_transport_system.swf





Figure 7-6 Oxidative Phosphorylation Source: Di Giuseppe et al. 108 By the end of this process, one molecule of glucose generates 36 ATP molecules.



Energy Summary Glycolysis 2 ATP……………………………………………………………………….2 ATP 2 NADH to the ETC x 2 ATP generated = 4 ATP Krebs Cycle 2 GTP converted to 2 ATP = 2 ATP 8 NADH to the ETC x 3 ATP generated = 24 ATP 2 FADH2 to the ETC x 2 ATP generated = 4 ATP Total ATP ………………………………………………………………….36 ATP

Support Questions

4. a. Distinguish between an electron carrier and a terminal electron acceptor. b. What is the final electron acceptor in aerobic respiration? 5. Compare substrate-level phosphorylation and oxidative phosphorylation. 6. Describe how each of the following compounds contributes to the cellular

respiration process:

a. FADH2 b. pyruvate c. ATP synthase d. coenzyme A e. glyceraldehyde-3-phosphate

Anaerobic Pathways The glycolysis portion of cellular respiration is the only phase that is anaerobic. When oxygen is not present, this phase is able to continue, at least for a period of time. The limiting factor for this pathway is the availability NAD+ to be reduced to NADH. If NADH cannot be oxidized, glycolysis will eventually shut down and no energy will be produced. This means death for the cell and the whole organism. Organisms have evolved two main pathways that allow glycolysis to continue when oxygen is not available. Both methods involve transferring the hydrogen atoms of NADH to other organic molecules in a process called fermentation. We will examine ethanol fermentation used by yeast cells and lactic acid fermentation used by multi-cellular organisms such as ourselves.



In ethanol fermentation, NADH transfers its hydrogen atom to acetaldehyde which leads to the formation of ethanol. Yes, this is the alcohol that we drink. This transfer frees up NAD+ molecules and glycolysis can continue to produce its two ATPs. For the yeast cell, the energy generated is enough to satisfy the organism’s energy needs. Humans have learned to manipulate this metabolic process to their own advantage. In beer and winemaking, yeast ferment sugars found in various fruit juices, releasing CO2 and ethanol. Baked goods also rely on yeast. The release of CO2 during fermentation causes dough to rise while the ethanol produced is burned off during baking. Lactic acid fermentation occurs in muscle cells when not enough oxygen is available to power the aerobic portion of the cellular respiration pathway. You experienced this in the activity with the clothespin at the beginning of the lesson. As oxygen became unavailable, the NADH molecules transferred their hydrogens to pyruvate which regenerated NAD+ and allowed glycolysis to continue. This transfer converted the pyruvate to lactate or lactic acid. As lactic acid continued to build up in those muscle cells, your fingers became stiff, sore and eventually fatigued to the point of not working. We experience this on a more system wide level when we exercise vigorously. This pathway can be reversed when oxygen is again present. Lactic acid is transported to the liver where it is oxidized back into pyruvate which can then continue through the other oxygen-requiring phases of cellular respiration.

Figure 7-7 The Fermentation Pathways Source: Di Giuseppe et al. 120



Support Question

7. List two differences between aerobic respiration and fermentation. Comparing Photosynthesis and Cellular Respiration Photosynthesis and cellular respiration are closely related and considered to be interdependent. Plants contain both chloroplasts and mitochondria and can undergo both processes while animals are only capable of cellular respiration. In terms of their interdependence, plants may be responsible for converting sunlight energy into a food source for all, but, without the by-products of cellular respiration, carbon dioxide would be in short supply. Simply put, the products of photosynthesis, namely glucose and oxygen are the reactants of cellular respiration while the products of cellular respiration, carbon dioxide and to some extent water are needed for photosynthesis. Both organelles have similar structures which are used for similar purposes such as the inner membrane being folded to create more surface area, the presence of an electron transport chain embedded in the inner membrane and used to create ATP and the presence of enzymes within that ETC that are similar or exactly the same. The similarities go on and on but the point is that both processes have developed over evolutionary time as a means to create the energy cells need to perform its essential functions.

Figure 7-8 A Comparison of Photosynthesis and Cellular Respiration Source: Di Giuseppe et al. 179



Key Question #7

1. If carbohydrates are unavailable for cellular respiration, other organic molecules can be broken down and enter the cellular respiration process at the appropriate spot. Proteins can be broken down into a variety of amino acids. Some amino acids can be converted into glutamate which can then be converted into alpha- ketoglutarate. State which steps of the cellular respiration pathway, lead to the generation of the energy molecules. State the TOTAL number of ATP molecules the ONE of these converted alpha-ketoglutarate molecules can produce and explain how all the ATP molecules are generated. (8 marks)

2. Several vitamins, especially the B vitamins, play key roles in energy metabolism. A number of vitamin deficiencies, if left unchecked, can cause serious illness. Research the B vitamins riboflavin (B2) AND niacin (B3) and briefly describe the following: (16 marks)

a. their function in energy metabolism (2 x 2 marks = 4 marks) b. good natural sources of each vitamin (2 x 2 marks = 4 marks) c. the deficiency symptoms (2 x 4 marks = 8 marks)

3. Create a table like the following one and fill in the cells to compare

photosynthesis and cellular respiration based on the following: organelle, reactants, products, electron source, carrier molecule(s), location of ATP synthesis. (12 marks)

Category of Comparison Photosynthesis Cellular Respiration Organelle Reactants Products Electron Source Carrier Molecule(s) Location of ATP Synthesis


SBI4U


Lesson 8 – Cellular Energy


Introduction Over the last three lessons, you have learned about energy transformations and how they apply to the metabolic processes of photosynthesis and cellular respiration. The metabolic pathways that each process utilizes to convert energy into usable forms have been examined in detail. Overall, you should have a basic understanding of how both plants and animals either create or capture the organic molecules that store chemical energy. With this knowledge, you can now examine some of the wider implications of man’s attempt to control these processes. There are some definite benefits and some drawbacks to this control. Obesity and weight control has become a major issue in North American society. Proper nutrition is essential to good health and leads to a healthy weight. There are many diets and weight control supplements that may do more harm than good. Weight control drugs that were approved for use were proven to be dangerous and sometimes deadly. Advertisements for diet pills and miracle diets are everywhere claiming miraculous results. This creates a lot of confusion but, a little knowledge of metabolism goes a long way. Scientists have turned to some plants and microbes (bacteria) in the hopes of using their metabolic processes to help improve the environment. Some of these organisms are capable of either absorbing or metabolizing toxic waste materials. If used properly, studies show that they could help clean up oil spills or remove toxins such as cyanide from waterways. This has opened up a whole new area of research called bioremediation. What You Will Learn After completing this lesson, you will be able to: • Analyse the role of metabolic processes in the functioning of and interactions

between biotic and abiotic systems such as the use of microbes in bioremediation • Assess the relevance, to one’s personal life and to the community, using one’s

understanding of cell biology and related technologies such as knowledge of metabolic processes and its relevance to personal choices about exercise, diet and the use of pharmacological substances

Thought Questions Use these questions to think about the implications of altering body metabolism. 1. Do fad diets work? 2. What is the healthy way to lose weight? 3. Should people use diet pills and are they safe? 4. How can plants and other organisms be used to improve the environment?



Nutrition and Cellular Energy Although most people are aware that a balanced diet is important for good health, not many actually understand the role that the various nutrients play in the body. As we learned earlier, glucose, a carbohydrate, is the main fuel source for generating ATP. Excess carbohydrates can be stored short term as glycogen in muscle and liver cells. When the body requires additional energy, the glycogen can be quickly converted back into glucose and enter the cellular respiration pathway. Good dietary sources of carbohydrates include pasta, rice, whole grains and bread. The more complex carbohydrates are recommended over the simpler ones. Complex carbohydrates tend to have a more complex molecular structure that takes longer for the body to break down. This allows the feeling of fullness to last longer without sending you back to the refrigerator. They also contain more vitamins and dietary fibre which are missing from the more refined carbohydrates like sugar, white rice and white bread. Fats have long been maligned as being bad for your health. It is not the fats themselves that are unhealthy but the amount of fatty foods that are ingested in the North American lifestyle. Fats are also known as lipids and can be used to generate ATP when carbohydrates are not available. When digested, fats are broken down into glycerol and fatty acids. Glycerol can be converted into PGAL and enter the cellular respiration path during glycolysis. Fatty acids can be stored as fat or converted into a 2-carbon fragment that can form acetyl CoA which can then enter the Krebs cycle. Dietary sources of this molecule include butter, cream, margarine and oil. They are also found in meats and nuts. The plants oils are recommended over the animal fats as being healthier. It may not be the body’s first choice, but proteins can also be broken down and used to generate ATP. The various amino acids can be converted into different substances that can enter the cellular respiration pathway in many different places. This important macromolecule can be found in red meat, poultry and seafood, eggs and milk products and from plants, beans, peas and nuts are also good sources. Cereals and pasta also contain some proteins. It is recommended that approximately 60-65% of a person’s daily energy requirements should come from carbohydrates, 30-35% from fats or lipids and the rest from protein. According to Canada’s Food Guide, adults should ensure that they have 7-10 servings of vegetable and fruit, 6-8 servings of grain products, 2 servings of milk and alternatives and 2-3 servings of meat and alternatives to stay healthy. This allows the body to meet its need for vitamins, minerals and other nutrients and contribute to good health. It will also reduce the risk of obesity, type 2 diabetes, heart disease and certain types of cancer and osteoporosis.



Fad Diets According to the experts, the safest and most reliable way of losing weight and keeping it off is to change one’s lifestyle habits. This means cutting out about 500 calories a day and beginning an exercise routine. In many cases, cutting the excess calories means readjusting your serving selections to match or more closely match those recommended in the food guide. This will allow the extra weight to be taken off gradually. But, it is very tempting to give in to the ads we see on TV or read in a magazine, such as “Lose 30 pounds in 30 Days” or “Lose Weight While You Sleep”. Many skinny celebrities swear by one diet or another. Many diets don’t follow these guidelines but rather, severely reduce or completely eliminate one of the food groups. This can cause a person to lose weight in the short term but can be unhealthy from a metabolic standpoint. The Low Fat/No Fat Diet In this diet, people severely limit the fats that they eat. The fats are replaced by even more carbohydrates. The idea is that if you are not eating fats, your body cannot make fats. This is completely untrue. Glucose can be converted into other molecules such as glyceraldehyde-3-phosphate which in turn can be converted into glycerol (one part of the lipid molecule). It can also be converted into pyruvate which can be converted to acetyl CoA and then into fatty acids (the other part of the lipid molecule). Any excess energy, no matter what nutrient molecule it originally came from, can be stored as fat. With this diet, not only will fat continue to be created, the individual’s sugar levels will rise because of all of the extra carbohydrates.

Figure 8-1 The Conversion of Glucose to Fats Source: Blake et al. 79 The Low Carbohydrate/High Protein Diet This diet goes by a number of names and is often known by the author name of the latest diet craze book. No matter what it’s called, the basic idea is that the dieter eats an unlimited amount of protein such as meats, poultry, fish, cheese and eggs while allowing low amounts or no amount of carbohydrates. This would mean eliminating



such foods as most vegetables, sweets, rice, pasta, bread, fruits and milk. This does result in immediate weight loss but most of the weight lost is water. When a person goes back to eating carbohydrates, the water weight is regained. If the individual stays on the diet for a long time, eventually muscle and fat weight will be lost. Healthwise, there are many problems with this diet. Inadequate diets, not addressing all the food groups, tend to worsen chronic and acute conditions and make recovery from illness harder. The high protein and high fats can increase the risk of heart disease, cancers and kidney diseases. The lack of carbohydrates depletes muscle glycogen stores and can make exercise seem harder. It can also lead to conditions such as nausea, diarrhea, constipation and fatigue. A great deal of calcium is also lost when protein levels are high while calcium intake is low because of diet restrictions. But, the most dangerous problem is ketosis. This is a process where ketones, such as acetone, build up in the blood due to incomplete breakdown of stored fats. This causes very bad breath and can cause the pH of the blood to become more acidic. If the pH of the blood is altered too greatly, proteins and enzymes stop working properly and this can actually lead to death. Diet Pills and Medications Weight reducing medication can be divided into two categories: prescription drugs and over the counter drugs. The latter group tends to have smaller amounts of the active substance that supposedly makes them safer. There are also many natural or homeopathic products that contain ingredients that studies suggest, may have an effect on appetite. Regardless of the type, weight loss drugs have one of three mechanisms of action. A. suppression of appetite – These reduce the desire to eat and tend to contain

amphetamine-like substances. Some of the side effects include increased blood pressure, dry mouth, constipation, headache and insomnia. Example - Sibutramine or Reductil

B. increase the body’s metabolism – These drugs increase the rate of metabolism

by stimulating the central nervous system. These stimulants can be very addictive.

C. interference with the body’s ability to absorb specific nutrients in food – These

drugs, such as Orlistat, block the breakdown of fats, preventing fat absorption. Side effects include oily bowel movements, stomach pain and flatulence.

Weight loss medications have endured some bad press over the last decade with the introduction of such drugs as fen-phen and Redux. Fen-phen is actually a combination of the two drugs phentermine and fenfluramine. It was the most commonly prescribed diet medication in the 1990’s. Dexfenfluramine or Redux was developed as an alternative to fenfluramine as it had fewer side effects. Both drugs were removed from



the market in September 1997 when mounting evidence suggested that both could cause heart valve degeneration in up to 30% of those who had used it.

Support Questions

1. Keep a food log for three days. How close are you to following the Canada Food Guide in terms of number of servings in each of the food groups. Do you need to make any adjustments to your diet to provide a healthier mix of dietary energy sources?

2. Dinitrophenol (DNP) was a weight loss drug introduced in the 1930’s. It worked by making the mitochondrial membrane more permeable to H+ (the H+ leaked across the membrane more easily). This caused more production of heat but less ATP. a. How would this action lead to weight loss? b. What would be the dangers of using this drug?

Bioremediation Bioremediation involves using living organisms to clean up contaminated soil or water. There are three main types of this process. Biostimulation – Nutrients and oxygen are added to contaminated areas to encourage the growth and activity of naturally occurring bacteria that will break down the contaminant. Bioaugmentation – Organisms that can clean up a particular contaminant are added to the area. This tends to work better when the contaminant has been removed from the area and moved to a site when the conditions for growth of the organism can be maximized. Intrinsic Bioremediation – This type occurs naturally in water and soil. This tends to be seen in petroleum contamination sites where bacteria naturally begin to break down the contaminant. The reason that these processes work is that different bacterial species can use the contaminant molecules to release energy to power their biological processes. When the contaminant molecules are broken down, energy is released. Scientists are studying various bacterial species to determine which ones are suitable for the different contaminants. For example, in gold mining operations, cyanide, a very potent poison, is used to remove gold from the surrounding rock. Cyanide tainted water when released back into the ecosystem, kills all the living things in the area. Some companies are using bacteria that break down cyanide, to treat the water until the cyanide is removed



and then releasing it back into the ecosystem. The already contaminated areas have been exposed to the bacteria as well and have decreased the cyanide levels to the point where life can grow again. Research is also underway to use bacteria to clean up oil spills both on land and in the lakes and oceans. It is hoped that the bacteria will be able to break down the oil molecules and remove them from the environment. In March of 1989, the oil tanker Exxon Valdez ran aground and, in five hours, leaked approximately 258 000 barrels of oil into the waters off the coast of Alaska, contaminating about 300 miles of coastline. This disaster provided a natural laboratory for scientists to study how various bacterial species were able to promote the clean up of the region. Phytoremediation Phytoremediation is a form of bioremediation but uses plants instead of bacteria. This process makes use of a plant’s natural ability to contain, degrade or remove contaminants from water and soil. Scientists have begun using such plants as sunflowers, ragweed, cabbage and geraniums to help clean up contaminated sites. There are several advantages and disadvantages to using this form of remediation. Plants are environmentally friendly and cost-effective. They have the ability to clean up a large number of contaminants and in many cases, the metals that they absorb can be removed from the plant matter and recycled. Because their root systems push down into the soil, they are able to prevent or reduce contaminants from entering the ground water. On the negative side, remediation can take a long time because it relies on the natural cycle of plant growth. The contaminants can only be removed from areas within the reach of the plant’s root system. This is limited to approximately three to six feet for plants and ten to fifteen feet for trees. There is also a risk that of animals eating the contaminated plants and moving the poison into the food chain. There are five basic types of phytoremediation based on the whether the contaminant is a metal or an organic chemical. For metal extraction, the following methods are used: Phytoextraction – In this method, the plants physically absorbs the metals through the root system and move it to the upper portion of the plant such as the stems and leaves. The plants can then be harvested and discarded properly once the metals have been removed.



Figure 8-2 Phytoextraction Source: biology-online.org/phytoextraction Rhizofiltration – Plants using this method either absorb the contaminant directly into the roots or it is attracted to and held by the roots. This only works for surface and ground water remediation. Plants that are grown in clean water are replanted in the contaminated areas and when the roots are saturated with the contaminant, they are removed and replaced. This process has been used in artificially created wetlands to treat wastewater and contaminated water from landfill sites. Phytostablization – Rather than absorbing the contaminant, the plants are used to contain or at least slow down the movement of the contaminant. This can help prevent the contamination of ground water.



Figure 8-3 Phytoextraction Source: biology-online.org/phytoextraction For organic chemicals, there are two further types of remediation. Phytotransformation – In this process, plants are able to absorb the chemical and actually break it down into less harmful components through its metabolic processes. Rhizosphere Bioremediation – It is not the plants themselves that break down the contaminant but rather, they provide natural substances that microorganisms such as yeast, fungi and bacteria need to grow. Once the growth of these organisms is stimulated, their metabolic processes break down the material in question. Research into the different plant species that could be utilized is well underway. It is hoped that eventually, a seed bank of plants that can be used for the various contaminants will be established so that in the future, if a site is found to be contaminated, a plant species will be available to help solve the problem. Using plants to clean a site is much more environmentally friendly than the complete removal of the contaminated material. It is a good way to make use of our natural resources.

Support Questions

3. Describe the advantages and disadvantages of these natural remediation methods.



Key Question #8

1. One of the more recent popular diets is the South Beach Diet. Research this diet

and answer the following questions. (15 marks)

a. Describe how this diet is similar to the basic low carbohydrate diet. (2 marks)

b. Describe how this diet differs from the basic low carbohydrate diet. (8 marks)

c. Based on your knowledge, is this diet a safe way of losing weight? (5 marks)

2. One of the new weight loss miracle drugs is Hoodia Gordonii. Research this

substance and answer the following questions. (8 marks)

a. Where is it found? (2 marks) b. How does it work to control weight? (2 marks) c. Are there any potential side effects? (2 marks) d. What are the potential problems with obtaining this substance? (2 marks)

3. Arsenic is a chemical element that can cause death to humans and animals and

has been released into the environment through a number of industrial processes. It has been discovered that the Chinese Brake Fern grows well in contaminated soil and will take up the arsenic through phytoextraction. Research the Chinese Brake Fern and explain in a short report how it mediates contaminated soils and water. (10 marks)

4. Using the information presented below and your research from question #3,

answer the following questions:

• Typical arsenic concentration in contaminated soil is 100 p.p.m. or 100 mg of arsenic per kg of soil

• One brake fern can extract 38 mg of arsenic from the soil in 20 weeks.

a. How many harvests and how long would it take to phytoremediate this soil assuming the ferns grow year round? (2 marks)

b. Is it realistic to assume that the ferns will always be able to remove 38 mg of arsenic in 20 weeks? Explain. (2 marks)

c. What are some of the limitations that may affect the brake fern’s ability to phytoextract the arsenic? (2 marks)


SBI4U


Support Question Answers

SBI4U – Biology Support Question Answers

Lesson 5 1. The following are some examples of energy transformation. This is only a small

sample.

• A light bulb – electrical energy to heat and light • Fire – chemical energy to heat and light • Car engine – chemical energy (gasoline) to mechanical energy • Solar panel – light into electricity • Firecracker – chemical energy to sound and light • Glow stick – chemical energy to light

2. The First Law of Thermodynamics - Energy cannot be created or destroyed but

changed from one form into another.

The Second Law of Thermodynamic - Disorder (entropy) in the universe is always increasing. At every stage of transformation, there is increasing entropy.

3. An endergonic reaction is a non-spontaneous reaction where free energy is

taken up during the reaction and is stored. An endothermic reaction refers to the movement of heat in a system. In this case heat is absorbed by the system. An endergonic reaction is USUALLY endothermic but not always since entropy can play a role. An exergonic reaction is a spontaneous reaction where free energy is released. This is usually accompanied by a release of heat (exothermic) but not always.

4. The reaction will occur spontaneously because delta G is negative, meaning that

the amount of energy in the reactants is greater than that of the products and will therefore be released, making the reaction exergonic.

5. ATP is the “energy currency” of the cell or all living organisms. Many types of

organisms use many different mechanisms to release the energy stored in chemical bonds but, all convert it to ATP. It can be used to power all the diverse energy consuming processes an organism needs to survive from muscle contraction to active transport to creating complex molecules.

Lesson 6 1. The photosynthetic rate of the bean plant exposed to blue light will be much

higher than the bean exposed to green light because the pigments in the chloroplasts absorb more light in the blue wavelengths and blue light has more energy than green light.

2. Twelve carbon dioxide molecules must enter the Calvin cycle to produce one

molecule of sucrose, which requires 36 ATP and 24 NADPH.



3. Plants produce excess sugar during a sunny day so that the plant has enough carbohydrate (glucose) to generate the energy it requires using cellular respiration during dark or cloudy days.

4. The herbicide DCMU will not affect ATP initially, because of cyclic electron flow.

But, NADPH cannot be produced because the electrons are not released. After a short time, depending on light intensity and the rate of photosynthesis, ATP formation will stop because not more ADP molecules are available to be converted into ATP.

DCMU is an effective herbicide because it prevents the Calvin cycle from occurring and if no glucose is made, the plant will starve to death and run out of energy.

Lesson 7 1. The correct order should be: muscle cell, nerve cell, skin cell and fat cell. The

muscle cell needs the most energy because the heart muscles have to contract continually to keep the heart beating. The nerve cell is next since it uses up energy sending nerve signals from one part of the body to another. The skin cell does not require as much as it only need energy to run its basic cellular functions. The fat cells require almost no energy since they do nothing but accumulate fat.

2. If an organism lacked the first enzyme in the glycolysis pathway, cellular

respiration would not be able to occur because the reactant for the next reaction would never be produced.

3. One molecule of glucose stores more energy than two molecules of pyruvate

because some of the potential energy in the glucose molecule has been released and passed on to the 2 ATP molecules and the 2 NADH molecules. Some of the energy would also be dissipated as heat.

4. a. An electron carrier is first oxidized and then reduced when another molecule picks up the electrons but a final electron acceptor is only reduced since it is the last molecule to receive the electrons.

b. The final electron acceptor in aerobic respiration is oxygen.

5. Substrate-level phosphorylation generates ATP directly from an enzyme

catalyzed reaction while oxidative phosphorylation generates ATP indirectly through chemiosmosis. The process is oxidative because it involves several sequential redox reactions, with oxygen being the final electron acceptor. It is more complex than substrate-level phosphorylation and it produces far more ATP molecules for every glucose molecule processed.



6. a. FADH2 is an electron carrier from the Krebs cycle that transfers its two electrons to an acceptor in the electron transport chain

b. pyruvate is the molecule produced at the end of glycolysis that is able to enter the mitochondrian to undergo pyruvate oxidation and then enter the Krebs cycle

c. ATP synthase is an enzyme complex located in the inner mitochondrial

membrane that uses the proton motive force to generate ATP

d. Coenzyme A is a substance derived from a B vitamin that attaches to the oxidized pyruvate molecule allowing it to enter the Krebs cycle

e. glyceraldehyde-3-phosphate is the molecule produced in the last step of

the energy investment phase of glycolysis which is then able to continue through to the energy payoff stage of glycolysis

7. Two differences between aerobic respiration and fermentation are: aerobic

respiration requires oxygen while fermentation does not and aerobic respiration yields 36 ATP molecules, carbon dioxide and water while fermentation yields 2 ATP molecules, and ethanol or lactic acid.

Lesson 8 1. Responses will vary depending on one’s diet but typically in North America, we

eat more grain servings and meat and alternatives servings than are healthy. Most of us need to increase our servings of fruits and vegetables.

2. a. Because a lot of the energy was lost as heat, more glucose and other molecules needed to broken down in order to generate enough energy for the cells to operate properly. This meant that the system was using more stored energy in the form of fat and thus weight loss occurred.

b. The dangers of this drug was that fact that the energy was released as heat rather than being converted to ATP. This caused the overall temperature of the body to rise. If the temperature became too high, the body’s enzymes stopped working and death could occur.

3. The advantages are: it is better for the environment with less disruption to the

other plants and animals in the area, its may be more cost effective, it allows the contaminants such as metals, oils and other toxic waste to be removed and can prevent it from reaching the ground water.

The disadvantages are: it can take a long time, sometimes years before a site is decontaminated, if animals eat the plants that are absorbing the toxin it may harm them and it is limited to where bacteria and plants will grow.


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SBI4U - Durham District School · PDF fileSBI4U – Biology Lesson 5 ... This transformation occurs during cellular respiration as the glucose molecules are broken down releasing not