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Biology 12 Answer Key Unit 2 • MHR TR 1

Answer Key

Unit 2 Metabolic Processes

Answers to Unit 2 Preparation Questions (Assessing Student Readiness)(Student textbook pages 108–11) 1. d

2. e

3. Intermolecular forces (London dispersion specifically)

4. a. reactants b. products

5. Formation of gas, colour change, precipitate formation, release or absorption of energy

6. b

7. substrate

8. The structure is made of intramolecular interactions causing folding, twisting due to the R groups. Its function is to loosely bond to the substrate decreasing the energy in bonds and making them easier to break.

9. Changing the temperature or pH.

10. a. amino acids b. simple sugars (monosaccharides) c. nucleotides

11. neutral

12. Enzymes decrease the activation energy needed for a reaction to progress. The energy of the reactants must be increased before the bonds break and the energy of the products decreases. Energy must be released during this reaction.

13. The cell membrane is made of phospholipids and proteins. The phospholipids have a hydrophyllic (polar) head and hydrophobic (nonpolar) tail. The head is attracted to water and the tail is repelled. When placed into solution, the tails spin away from water and a bilayer forms. It is a mosaic because it is made of discreet components (that are not bonded). It is fluid because the components are flexible and can move from place to place in the membrane. See Figure 2.12 on page 69 of the student textbook.

14. The cell wall provides structure to the cell. Plants need the cell wall to keep the plant rigid. The cell wall allows the plant cell to maintain turgor pressure. Animal cells do not need this structure due to the fact that animals make specialized cells to give them structure (e.g., bones, calcium deposits) if needed.

15. 1—microtubule 2—actin filament 3—intermediate filaments 4—lysosome 5—centrioles 6—centrosome 7—cytoplasm (or cytosol) 8—vesicle 9—Golgi apparatus 10—nuclear envelope 11—chromatin 12—nucleolus 13—nuclear pore 14—rough endoplasmic reticulum 15—smooth endoplasmic reticulum 16—ribosomes 17—peroxisome 18—mitochondrion 19—chain of ribosomes

16. The mitochondria break down high energy organic molecules to convert stored energy into usable energy in the form of ATP. They perform cellular respiration and are responsible for the complete oxidation of organic molecules to carbon dioxide.

17. Oxygen crosses the membrane by passive transport/simple diffusion from the blood into the cell and then into the mitochondria.

18. 1—central vacuole, water storage and support for cell 2—nucleus, contains DNA which stores and replicates

genetic information 3—chloroplast, photosynthesis 4—mitochondrion, cellular respiration

19. Chloroplasts act as the engines of photosynthesis. They contain chlorophyll, which absorbs light energy and are the site of the redox reactions that convert carbon dioxide and water into energy-rich carbohydrates and oxygen (as a waste product).

2 MHR TR • Biology 12 Answer Key Unit 2

20. The chloroplast and mitochondrion both transform energy from one form to another. The mitochondria releases energy from organic compounds and the chloroplast converts light into chemical potential energy.

21. 1—hair (trichome) 2—cuticle 3—upper epidermis 4—palisade mesophyll 5—mesophyll 6—spongy mesophyll 7—lower epidermis 8—cuticle 9—stomata/guard cell 10—vein

22. e

23. b

24. The vein transports water and minerals into the leaf and the products of photosynthesis out of the leaf.

25. Plant cells have chloroplasts, cell wall, and a large central vacuole. Only animal cells have lysosomes or centrioles. Plant cells are larger and have a more structured shape than animal cells.

26. Diffusion is the movement of particles from an area of high concentration (the initial drop of food colouring) to an area of low concentration (the surrounding water). This happens until equilibrium is reached (the water is all pink).

27. Only some molecules will be able to cross the membrane.

28. The water level will rise on the side containing urea. Osmosis occurs from the area that has higher water concentration to the area that has lower water concentration.

29. Facilitated diffusion requires carrier or channel proteins. They allow molecules that cannot travel through the phospholipid membrane to enter or leave the cell. This is necessary when a chemical is polar, large, or charged.

30. Active transport requires ATP to occur. Molecules move from low to high concentration. Passive transport occurs randomly from high to low concentration and does not require ATP.

31. facilitated diffusion

32. a. Na+ is forced into the cell down its concentration gradient. This process is coupled to the movement of glucose against its concentration gradient by the transport protein. The energy in the sodium gradient is used to create a glucose gradient. This is called a symporter.

b. The energy in the sodium gradient. ATP was the source of energy to create. the sodium gradient

c. Active transport or, more specifically, secondary active transport using a symporter.

33. Diffusion happens from high to low concentration. If the concentration of solutes in water is high, the concentration of water must be low and vice versa. This means that in a less concentrated solution, water is in high concentration.

34. Wavelength is the distance between two crests.

35. Only certain wavelengths stimulate receptors (rhodopsin) in our retina. Visible light is made of those wavelengths that those receptors can detect.

36. Light can be transmitted, reflected, refracted, or absorbed depending on the opacity, optical density, lustre, and colour of the material that the light hits.

37. Fossil fuels are composed of ancient organisms that once photosynthesized and stored the Sun’s energy.

38. Wasting energy means using it inefficiently, such that energy is lost to the environment rather than performing the task.

39. Sample answer: A drumstick moves through the air (mechanical) and hits a drum membrane (sound).

40. Sample answer: Heat is transferred from a fire, to a pot, then to the pot’s contents.

41. Autotrophs create chemical energy from sunlight through photosynthesis. Heterotrophs must consume chemical energy. Both autotrophs and heterotrophs then convert the chemical energy into useful energy to power life processes.

42. ATP, NADPH

Chapter 3 Energy and Cellular Respiration

Answers to Learning Check Questions(Student textbook page 118) 1. Metabolism refers to all reactions occurring in an

organism, including those that build new compounds (anabolism) and those that break them down (catabolism).


2. Anabolic reactions decrease entropy and require energy to be put into the system (they are endergonic) and catabolic reactions increase entropy and release energy (they are exergonic).

3. Whenever a chemical bond forms between two atoms, energy is released. This causes the amount of chemical energy in the molecule to decrease each time a bond forms.

4. Energy cannot be created or destroyed, but it can be transformed from one type into another and transferred from one object to another. This means that the total amount of energy in the universe remains constant.

5. Since the universe must tend toward disorder, compounds must have a natural tendency to break apart, which would increase entropy if this energy were not converted to other forms such as heat.

6. Free energy is the energy available to do work in an organism. An endergonic reaction requires an input of free energy. An exergonic reaction releases energy. Entropy is related to the constant input and release of energy.

(Student textbook page 124) 7. Cellular respiration includes the catabolic pathways

that break down energy-rich compounds to produce ATP, while aerobic respiration refers to those pathways that require oxygen in order to proceed.

8. C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(ℓ) + energy Since cellular respiration takes more than two dozen

reactions and this shows only one step, the arrow must represent a summary of those processes.

9. Glycolysis-cytosol (not in mitochondria); pyruvate oxidation and Krebs cycle (mitochondrial matrix); oxidative phosphorylation (inner mitochondrial membrane).

10. The process in which two molecules of ADP are converted to two molecules of ATP (at reaction seven in glycolysis) for every molecule of glucose entering glycolysis.

11. Oxidative phosphorylation is the formation of ATP (after the Krebs cycle is complete) using energy obtained from redox reactions in the electron transport chain.

12. Glycolysis is the metabolic pathway that breaks glucose into two pyruvate molecules (ATP).

(Student textbook page 128) 13. NAD+ is reduced to form NADH, an energy-rich

electron carrier that allows for the production of ATP.

14. The Krebs cycle is the cyclic metabolic pathway that acquires acetyl-CoA and ultimately oxidizes it into carbon dioxide while regenerating the compound that picks up more acetyl-CoA. It converts released energy to ATP, NADH, and FADH2. Its importance is in the production of large quantities of NADH and FADH2, which generate more ATP than would be formed if substrate-level phosphorylation had occurred instead of oxidative phosphorylation.

15. Pyruvate loses a carbon in the form of CO2 and is oxidized by NAD+, resulting in NADH. The remaining two carbons are attached to a co-enzyme called CoA.

16. Each molecule of glucose produces two molecules of pyruvate. Each pyruvate goes through the Krebs cycle independently.

17. Reactions 4, 5, and 7.

18. Reactions 4 and 5 generate CO2 and NADH, (isocitrate combines with isocitrate dehydrogenase which allows NAD+ to remove an H atom, oxidizing isocitrate, releasing CO2, and forming NADH. This repeats in reaction 5 with the enzyme α-Ketoglutarate dehydrogenase).

ATP is produced in reaction 6 by substrate level phosphorylation, a complex reaction in which a phosphate group replaces the CoA while the substrate, succinate, is bound to the enzyme. The phosphate group is then added to a molecule of guanosine diphosphate (GDP) forming guanosine triphosphate (GTP). The terminal phosphate group from GTP is then transferred to ADP to produce ATP.

FADH2 is produced when FADH is reduced by the oxidation of succinate in reaction 7.

Answers to Caption QuestionsFigure 3.1 (Student textbook page 114): Bricks, boards, and cement have more entropy than the building does. When the building is put together, the entropy decreases. Demolishing the building would be a catabolic reaction.

Figure 3.3 (Student textbook page 115): Answers could include thermal energy, as this is the usual waste product associated with light.

Figure 3.5 (Student textbook page 118): Graph B, since energy is released to form the products. Glucose has more potential energy than carbon dioxide and water does.

Figure 3.15 (Student textbook page 131): Acetyl CoA


Answers to Section 3.1 Review Questions(Student textbook page 121) 1. Metabolic pathways are step-by-step sequences, in

which one substrate or more is changed into a product, and the product becomes a substrate for a subsequent reaction. A unique enzyme catalyzes each of these reactions. In the absence of enzymes, the reactions would not occur fast enough to sustain the life of the cell.

2. Diagram should look like Figure 3.1 on page 114 of the student textbook. With the reactants and products labelled and the energy changes identified.

3.

Type of Energy Description Example

Kinetic energy

Energy of motion. A boulder rolling down a hill.

Potential energy

Stored energy. A boulder at the top of a hill.

Thermal energy

The kinetic energy of particles.

As an object gains heat, the particles move faster.

Chemical energy

Potential energy stored in the arrangement of bonds.

The bond between carbon and hydrogen in methane (CH4) provides potential energy for combustion.

Bond energy

The energy required to break a chemical bond.

Two oxygen atoms bonded to each other to form O2 are sharing electrons to fill their valence shells and are more stable than the two separate oxygen atoms.

a. Potential energy before bonding, and chemical energy after bonding.

b. Thermal energy is kinetic energy based on the movement of particles and chemical energy is potential energy stored in the arrangement of bonds.

4. The first law states that energy cannot be created or destroyed, but it can be transformed from one type into another and transferred from one object to another. This means that energy is transferred during chemical reactions between the bond energy and chemical potential energy, thermal energy and kinetic energy.

The second law states that during any process, the universe tends toward disorder. For any spontaneous process to occur, there must be a loss of “free energy” (energy that is able to do work) in the form of “unusable” energy (heat) that will contribute to increasing the overall disorder of the universe. So every time there is a change of energy from one form to another, some must be “lost” to the system in the

form of heat. A process can increase the “local” order of a system, but energy must be expended as heat to increase the overall disorder of the universe. For example, it is impossible to clean and organize your room (a decrease in local entropy) without using a lot of chemical and kinetic energy and emitting some energy as heat, which increases the overall entropy of the universe.

5. An open system exchanges matter and energy with its surroundings. A closed system does not. The first law of thermodynamics refers to open systems; the second law of thermodynamics applies to closed systems

6. Living things themselves are not closed systems. They use inputs of matter and energy to reduce their local entropy. This energy comes from the sun. Therefore, energy is transferred from one to the next (first law) and energy is expended to reduce entropy (second law).

7. As the particles separate, they are more free to move, this means that the entropy has increased.

8. a. A shows an endergonic reaction in which the products have more free energy than the reactants. This reaction is not spontaneous. B shows an exergonic reaction in which the products have less free energy than the reactants. This reaction is spontaneous.

b. A needs energy, B releases energy.

9. The reactants have more free energy than the product, so a spontaneous reaction occurs without the input of energy.

10. Anabolic reactions usually decrease local entropy. This makes them tend to be endergonic. They require an input of energy, so the change in free energy would be positive.

11. Diagrams should resemble Figure 3.6 on page 119 of the student textbook. Adenine, phosphate group and ribose should be clearly labelled.

12. Diagrams should resemble Figure 3.7 on page 120 of the student textbook with ATP, ADP, and Pi clearly labelled. Energy is input into the world from the Sun. This energy is transferred to ATP, which can then be transferred to other molecules when the third phosphate from ATP is transferred to become ADP. Endergonic reactions are often powered by ATP. Exergonic reactions can produce ATP.

13. Reduction occurs when a chemical receives electrons from another chemical. Oxidation occurs when it loses electrons to another chemical. They are linked because there must be a donor and a recipient for the electrons.


14. By recycling the electron carriers and ATP, the cell has a constant capacity for redox reactions. Once a carrier loses its electrons, it can then go pick up new ones. It keeps the ATP cycle going so that energy can continue to be transferred and power life processes.

Answers to Section 3.2 Review Questions(Student textbook page 133) 1. Aerobic respiration is the metabolic pathway that

breaks down energy-rich compounds to produce ATP and requires oxygen to proceed. C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

2. Tables should resemble Figure 3.9 on page 123 of the student textbook.

3. In the cytosol, glycolysis breaks glucose into two 3C molecules and energy. In the mitochondrial matrix, the 3C molecules are made into 2C molecules (acetyl CoA) which then enter the Krebs cycle, generating intermediate energy carriers and ATP. The NADH and FADH2 created are converted to ATP through oxidative phosphorylation on the inner mitochondrial membrane.

4. Substrate level phosphorylation is the conversion of ATP to ADP or vice versa on an enzyme. Oxidative phosphorylation is the use of electron transport chains to generate ATP chemiosmotically.

5. To break down glucose into pyruvate and generate ATP and NADH. Water also results.

6. a. The pathway oxidizes acetyl CoA to CO2, regenerates a compound that connects to acetyl CoA so that the cycle can continue and creates ATP, FADH2 and NADH.

b. acetyl CoA is formed from pyruvate by oxidation and release of CO2

c. NAD+ and FADH+

7. It effectively converts the energy stored in NADH and FADH2 to energy in the form of ATP. By oxidizing these two energy-rich compounds, it also forms NAD+ and FAD which are needed by the Krebs cycle, which will reduce them again while oxidizing carbon.

8. The electron transport chain is a series of electron carriers and proteins that are embedded in the inner membrane of the mitochondrion. Electrons donated by NADH and FADH2 are transported through this chain, providing the energy needed for oxidative phosphorylation.

9. Yes, because they pick up their passengers (electrons and hydrogen) during glycolysis (pyruvate oxidation and Krebs) and drop them off at the electron transport chain. They are not changed in the process and, once their passengers are dropped off, they go pick up new ones.

10. Chemiosmosis is the process that uses energy in a hydrogen ion gradient across the inner mitochondrial membrane to drive phosphorylation of ADP to form ATP. ATP synthase catalyzes the phosphorylation of ADP. Most of the energy of cellular respiration is generated by this reaction.

11. The Krebs cycle requires NAD+ and FADH+ to reduce pyruvate. If there is no oxygen, the electron transport chain does not pass electrons to it to produce water. This means that electrons are not taken from the NADH and FADH2, and therefore NAD+ and FADH+ are not available. As glycolysis also uses up NAD+, it would also ultimately be inhibited by a lack of oxygen as well. However, if fermentation takes place, it can use up the NADH produced by glycolysis and supply the NAD+ required.

12. If the electron transport chain is inhibited, very little ATP is produced, and human metabolism would not have enough energy to continue.

13. Some protons leak through the inner mitochondrial membrane without passing through an ATP synthase complex. Some of the energy from the hydrogen ion gradient in the mitochondria is used to transport pyruvate molecules generated during glycolysis from the cytoplasm into the mitochondria. And, some energy is used to transport ATP out of the mitochondria for use in the cytoplasm.

14. feedback inhibition

15. a. iii, ii, i, iv, v b. ATP generation in mitochondria arises from

chemiosmosis. In this process, electron transport coupled to proton transport generates a proton gradient across the inner mitochondrial membrane. This gradient powers the phosphorylation of ADP to form ATP.

16. Diagrams should show an enzyme with active sites for ADP and Pi. ATP is the product. See chemiosmosis Figure 3.13B on page 128 of the student textbook. Sample caption: Aerobic respiration requires the oxygen released by substrate-level phosphorylation.


Answers to Section 3.3 Review(Student textbook page 137) 1. Anaerobic respiration is a metabolic pathway in which

an inorganic molecule other than oxygen is used as the final electron acceptor during the chemiosmotic synthesis of ATP. This occurs in the cytosol of bacteria, yeast, and animal muscle cells in the process of fermentation.

2. Fermentation is a form of anaerobic respiration. During anaerobic respiration, the final electron acceptor in bacteria can be nitrate or carbon dioxide. During fermentation, NAD+ is regenerated throughan alternate method and there is no ETC.

3. There is no oxygen to drive the ETC. This means that an alternate electron receptor is needed or that the ETC does not occur. All of the energy comes from glycolysis. Glucose cannot get completely oxidized.

4. a. Fermentation b. A—yeast, B—muscle cells c. Allows glycolysis to continue since NAD+ must be

available to continue to process glucose.

5. The Krebs cycle does not occur, so not as much NADH and FADH2 is made. Therefore, the ETC does not happen and chemiosmosis does not happen.

6. They use an alternate final electron acceptor to oxygen. For example, methanogens use carbon dioxide.

7. Anaerobic respiration causes lactate to form in muscles, which causes pain and extends recovery time, interfering with the athlete’s ability to perform.

8. Risks include: costs more than gasoline, requires a lot of grain/crop land, only 10% ethanol is made and must be processed, distillation requires a lot of energy, toxic and flammable products can be made

Benefits include: renewable resource, cleaner combustion, can make other organics (e.g., acetone)

9. Both require NAD+ as an oxidizing agent, include the production of pyruvate, and don’t require oxygen. Glycolysis stops at the production of pyruvate. Anaerobic processes regenerate NAD+ but glycolysis itself does not. Anaerobic processes use electron acceptor other than oxygen to generate NAD+.

10. Answer should demonstrate an understanding of the process of anaerobic respiration and the production of ethanol, and the pros and cons of using pig manure for the process (page 136 of the student textbook provides general pros and cons of biogas).

Answers to Chapter 3 Review Questions(Student textbook pages 147–51) 1. c 2. a 3. e 4. b 5. b 6. e 7. a 8. a 9. e 10. b 11. d 12. b 13. d 14. c 15. Glycolysis—cytosol; reactants: glucose, NAD+, ADP,

Pi; Products: pyruvate, H2O, NADH, ATP Pyruvate oxidation—inner membrane of mitochondria;

reactants: pyruvate, NAD+, CoA; products: CO2 + NADH + acetyl-CoA

Krebs cycle—matrix; reactants: acetyl-CoA, NAD+, FAD, H2O; products: CO2, NADH, ATP, FADH2

Oxidative phosphorylation—inner membrane; reactants: NADH, FADH2, O2, ADP, Pi; products: NAD+, FAD, H2O, ATP

16. In the absence of oxygen, pyruvate is changed into lactate or alcohol. If oxygen is present, pyruvate is converted to acetyl-CoA and enters the Krebs cycle.

17. The first product in the Krebs cycle is citric acid. It has three carboxyl functional groups.

18. NADH provides electrons for the electron transport chain. They are passed to oxygen to make water. It also creates a proton gradient which powers the synthesis of ATP during chemiosmosis. Once NADH is oxidized, it can pick up new electrons at an earlier stage.

19. If it didn’t, the Krebs cycle would not continue and no more NADH, FADH2, or ATP could be generated. A deficiency would cause fatigue and a build up of lactate, which could cause tissue damage.

20. The molecules are converted and enter cellular respiration at different stages. Proteins (amino acids) are converted to pyruvate or another intermediate in glycolysis or the Krebs cycle. The glycerol portion of fats is converted to G3P and enters glycolysis at that step. The fatty acid portions are converted to acetyl-CoA, and enter the Krebs cycle.


21. They act as inhibitors.

22. Energy must be input to form (be stored in) the bonds as entropy decreases.

23. They release energy that can be picked up by ATP and transferred to other molecules for cell processes. They create free energy.

24. Energy is the ability to do work. Kinetic energy is free energy (energy of motion in bodies or particles). Potential energy is stored in chemical bonds.

25. Bond energy arising from the breaking of chemical bonds is used by cells to drive endergonic reactions such as the production of ATP.

26. To maintain life (a highly ordered low-entropy state), energy must be constantly input and transferred to molecules to power reactions (create ATP). When anabolic reactions occur, they use ATP and this energy must be replaced. The sun provides the input required.

27. Children are growing. This requires a great deal of anabolic reactions which decrease entropy. To fight entropy, energy is required.

28. Catabolic reactions have a negative ∆G because entropy increases and energy was released. When ∆G is negative, the reaction is exergonic. Anabolic reactions have a positive ∆G, which requires an input of energy. When ∆G is positive, the reaction is endergonic. If entropy increases in a reaction, the ∆S will be positive and contribute to a negative ∆G. Meaning this increasing entropy contributes to making reactions spontaneous. A decrease in ∆H would do the same.

29. For every ATP produced, an ADP is produced. Each used ATP must be replaced quickly. Also, ATP production and use are coupled to catabolic and anabolic reactions, and in chemiosmosis, ATP production is coupled to the proton gradient.

30. If catabolic reactions were to stop, ATP production would stop. The organism would not have any energy as it would all be chemical potential energy and not available for life processes.

31. If no ATP could be produced, the flow of energy in the ecosystem would be halted.

32. The energy used and released is not thermal energy, as implied by the terms endothermic and exothermic, it is free energy in the form of ATP. Endergonic and exergonic also include the concepts of entropy and energy changes.

33. The supply of glucose must be replenished to provide the energy needed to maintain tissue function. The person cannot eat, so the IV is the only way to input those raw materials.

34. To provide the hydrogen gradient needed to power chemiosmosis and the electrons for the electron transport chain.

35. Yes, they could be potentially oxidized fully to form CO2. This energy can be released if the lactate and ethanol are converted and enter cellular respiration to be further processed.

36. The energy can be thermal, to assist in the movement of compounds across a membrane, contraction of a muscle, or emit light in phosphorescent animals.

37. Bouncing, since the conversion is not fluid but occurs in discreet stages.

38. Diffusion occurs from areas of higher concentration to those of lower concentration. At high concentration, the entropy is low. The spontaneous movement to spread out increases the entropy. The second law states that entropy increases with any change.

39. The amount of energy released or gained depends on the amount of energy being stored or transferred and whether the randomness is increasing or decreasing.

40. Glycolysis—fructose 6 phosphate + ATP → fructose 1, 6-bisphosphate, and BPG + ADP → 3PG + ATP

Krebs cycle—succinyl-CoA + GDP + Pi → GTP + ADP → ATP, and one of succinate + FAD → fumarate + FADH2, or malate + NAD+ → oxaloacetate + NADH

41. fructose 6-phosphate + ATP → fructose 1, 6-bisphosphate fructose 6-phosphate + ATP; fructose 6-phosphate is the substrate

42. Sample answer: You have forgotten that there are two G3P molecules that go through reactions 6 to 10. This results in the production of four ATP molecules. Since two ATP molecules are consumed and four ATP molecules are produced, the net is two ATPs.

43. It is an enzyme that carries the acyl group to another molecule. It facilitates the transition.

44. Analogies should demonstrate an understanding of the role of ATP synthase in the generation of ATP using the hydrogen gradient. There should be some part of the analogy representing hydrogen, ADP, Pi, ATP, and ATP synthase. ATP synthase should bind the ADP and Pi.

45. Alanine could enter as pyruvate (as they both have three carbons). Aspartic acid and glutamic acid enter as oxaloacetate (as it has four carbons).


46. All organisms must convert the 6C sugar to a 3C sugar. Oxygen is not required for this stage. What differs is what happens to that 3C sugar in the absence of oxygen.

47. When alcohol is produced, carbon dioxide is produced. The carbon dioxide bubbles make the dough rise.

48. Experiments should demonstrate a method to capture and measure the amount of heat released and should have safety measures to control the burning of the ethanol. Typically, a hot water calorimeter can capture the released energy and the temperature changes can be used to calculate the heat transferred using the equation Q = mcT.

49. An anabolic reaction involves using energy to build large molecules from smaller molecules. In secondary active transport, energy from an electrochemical gradient is used to transport molecules or ions across a membrane.

50. A decrease, as many small pieces are being joined to make a larger piece, therefore the randomness has decreased.

51. By constant input of new glucose and coupling reactions and controlling the rate of cellular respiration by feedback inhibition.

52. a. the bond connecting the third phosphate b. It is exergonic. c. +30.5 kJ/mol would be needed to form the bond in

the endergonic reaction

53. A is the reactant(s) and B is the product(s).

54. By using alternate energy sources like lipids which can enter cellular respiration at the Krebs cycle.

55. CoA is needed in order for pyruvate to enter the Krebs cycle. If quantities are not high enough, less NADH can be made. NAD+ is needed to reduce chemicals in various stages and become NADH which generates ATP. Less ATP means less energy and more fatigue.

56. Diagrams should resemble Figure 3.5A on page 118 of the student textbook. The process is endergonic and the change in free energy is positive. Water (H2O) and carbon dioxide (CO2) are the reactants and methane (CH4) and oxygen (O2) are the products.

57. Diagrams should resemble Figure 3.6 on page 119 of the student textbook. ADP has one less phosphate group than ATP.

58.

ProcessChange in

Entropy

burning a piece of wood increase

table salt dissolves in water increase

a toy is assembled decrease

ice forms decrease

boxes are unpacked after you move houses increase

a librarian shelves books that were returned decrease

gases are absorbed into the blood from the lungs

decrease

59. Graphic organizers must include information from Figure 3.8 on page 120 of the student textbook. A flow chart would be a good choice.

60. Graphic organizers should include the information in Figure 3.10 on page 125 of the student textbook.

61.

Process Location ATP/

Reducing Power

glycolysis cytosol 2 ATP2 NADH

pyruvate oxidation mitochondrial matrix

2 NADH

The Krebs cycle mitochondrial matrix

6 NADH2 FADH2

2 ATP

Oxidative phosphorylation

inner mitochondrial membrane

32 or 34 ATP

62. See row 4 of Figure 3.9 on page 123 of the student textbook.

63. See Figure 3.10 on page 125 of the student textbook. (Numbered enzyme names can be omitted and replaced with the reaction name)

1, 3, 7, 10—oxidative phosphorylation 6—oxidation/reduction 2, 4, 5, 8—isomerization 9—dehydration

64. See the left side of Figure 3.17 on page 135 of the student textbook.

65. Answers should include: NADH—two produced during glycolysis; two

produced during pyruvate oxidation; lead to production of 3 ATP per NADH during oxidative phosphorylation; enter ETC at first protein (NADH dehydrogenase); lead to production of 28 or 30 ATP


Similarities—produced during Krebs cycle; lead to production of ATP during oxidative phosphorylation; are reducing agents

FADH2—two produced during Krebs cycle; lead to production of 2 ATP per FADH2; enter ETC at second protein (Q); lead to production of 4 ATP

66. All relate to the last steps of cellular respiration leading to the generation of ATP and occur on the inner mitochondrial membrane. The redox chain is formed by five electron carriers of differing redox potential (from least to most oxidizing). During oxidative phosphorylation, NADH and FADH2 are oxidized by the proteins and their electrons are passed to the next most oxidizing electron carrier until they are accepted by O2 which is the strongest oxidant. The protons are pumped across the membrane in reactions coupled to electron transport, and create a proton gradient across the membrane. Chemiosmosis occurs when the hydrogen ions pass through an ATP synthase complex and ATP is generated.

67. See Figure 3.8 on page 120 of the student textbook. Reducing power is the ability of a molecule to transfer electrons to another molecule. NADH and FADH2 have reducing power and are strong reductants. NADH has more reducing power than FADH2.

68. a. See Figure 3.13A on page 128 of the student textbook. The hydrogen gradient is analogous to the difference in height of water between the top and bottom of a dam. The water at the top has potential energy. When it falls, it causes the turbines to turn and leads to the formation of electricity. This is like the hydrogen gradient that has potential energy which causes the production of ATP as hydrogen ions pass through ATP synthase. Also, the ATP synthase “spins” as the protons move though the membrane, just like the turbine spins as the water moves through.

b. ATP synthase is the generator. It “creates” energy as H+ pass through.

69. The pH, temperature, and amount of nutrients will affect how well the yeast grows. The build-up of acids could kill the yeast. When yeast cells have enough oxygen, they reproduce rapidly, using aerobic respiration to make ATP. Once the oxygen is used up, the yeast cells switch to ethanol fermentation. However, once the ethanol builds up, it becomes toxic to the yeast and the yeast will die. Therefore, it is important that there is sufficient oxygen throughout the culture medium.

70. a. The other 60 percent is given off as heat, which help regulate an organism’s temperature.

b. The energy available to do work decreases as more of it is transformed into unusable heat. Aerobic respiration generates a lot of heat. This heat ensures the overall increase in entropy of the universe and is thus a manifestation of the second law.

71. Fast-oxidative fibres do not need many mitochondria because they obtain most of their energy from glycolysis, which occurs outside of the mitochondria. Slow-oxidative fibres need mitochondria to carry out oxidative phosphorylation to generate ATP.

72. A sprinter needs to run fast for a short time, thus it would be beneficial to make ATP as quickly as possible. Fast-glycolytic fibres produce ATP quickly via glycolysis.

73. A long distance runner needs to keep moving for a long time, thus it would be beneficial to have a steady supply of ATP from oxidative phosphorylation. This process is also a much more efficient, as the runners fuel is oxidized completely through the Krebs cycle and oxidative phosphorylation, not just through glycolysis and fermentation.

74. Research should include information about anaerobic respiration in methanogens and alternate pathways for several food sources.

75. Bacteria that decompose algae use up oxygen in the process of aerobic respiration. The resulting lack of oxygen means that fish and other aquatic life cannot carry out aerobic respiration, so they die off.

76. The bacteria could remove essential nitrate from agricultural lands, which would be a problem since plants require nitrate to grow. On the other hand, these bacteria could be used to remove nitrate from sewage so that the nitrate would not end up in natural bodies of water where it could cause algal blooms.

77. Sample answer: Microbial fuel cell research could help scientists learn about the electron transport chain and the possible electron acceptors that bacteria can use.

78. Microbial fuel cells could be used for wastewater treatment and to generate electricity without the need to burn fossil fuels.

79. Sample answer: Yes, because so many critical processes involve chemical reactions. For example, redox reactions and the metabolic pathways in aerobic respiration


80. Different microorganisms produce different products from fermentation, each of which would have a distinctive flavour and properties including gas production or colour.

81. Antioxidants can donate electrons to oxidants in redox reactions. As a result, the oxidants will no longer be reactive and will not pull electrons away from cellular components such as proteins, lipids, and DNA.

82. An understanding of glycolysis is key to understanding this condition because phosphofructokinase regulates an important step early on in glycolysis: the conversion of fructose 6-phosphate to fructose 1, 6-bisphosphate. When phosphofructokinase is deficient, there is a build-up of fructose 6-phosphate and the previous compound in the pathway, glucose 6-phosphate. This knowledge provides a starting place for exploring various treatment possibilities that target glycolysis. For example, students may suggest that dogs could be treated with active phosphofructokinase or ADP (to activate the enzyme), or with substances that would block the enzyme’s inhibitors (citrate and ATP) from interacting with the enzyme.

83. Typically, when protons diffuse through ATP synthase, the energy released is harnessed to add phosphate to ADP, making ATP. However, if the potential energy of the concentration gradient is not harnessed chemically, the diffusion of the protons will generate heat.

84. Sugar costs less than that. It doesn’t make sense to buy it. The gains in energy would be minimal as you are only skipping the glycolysis stage.

85. By manipulating H ion permeability, the pH of blood and tissues can be altered beyond safe levels. These products “short circuit” aerobic respiration, resulting in less ATP production from the oxidation of NADH. Safe levels would be difficult to regulate, users could effectively starve themselves even while still consuming food if too many H ions passed through the membrane without going through ATP synthase.

86. A decrease in entropy. There is less randomness in a polymer than in its monomer subunits.

87. If oxygen is not available to accept electrons at the end of oxidative phosphorylation, the cell will not be able to do aerobic respiration and only 2 ATP of energy will be made (compared to 36 ATP). This is not enough energy to maintain body function. In addition, lactate will be produced which causes muscle pain and cramping.

88. A reduced hydrogen gradient would reduce the amount of ATP produced during chemiosmosis. This could lead to cell death and if it were widespread, tissue and organ failure.

Answers to Chapter 3 Self-Assessment Questions(Student textbook pages 152–3) 1. c

2. a

3. c

4. e

5. d

6. b

7. d

8. e

9. a

10. d

11. Anabolic pathways decrease entropy by building polymers from monomers. They are endergonic (require energy input). Catabolic pathways increase entropy by breaking down molecules and are exergonic (release energy).

12. Active transport, heat, muscle contraction, the emission of light in phosphorescent animals

13. During any process, the universe tends toward disorder. This only applies in a closed system that has no energy input. In living organisms, energy is input from the sun or food which fights entropy and enables anabolic pathways.

14. enthalpy and entropy

15. See Figure 3.5 on page 118 of the student textbook. An endergonic reaction occurs when products have more free energy than the reactants. Energy must be put into the system. An exergonic reaction occurs when products have less free energy than the reactants. Energy is released from the system.

16. ATP is regenerated as it is used, as long as raw materials are available. See Figure 3.7 on page 120 of the student textbook.

17. Substrate level phosphorylation results in the direct production of ATP from ADP and Pi on an enzyme. ADP and Pi are the substrate. Oxidative phosphorylation requires the use of intermediate energy carriers with reducing power (NADH and FADH2). Electrons are passed through a transport chain of proteins so that a hydrogen gradient forms, which powers ATP generation during chemiosmosis.


18. 1—a. intermembrane space; b. proton gradient, pyruvate oxidation

2—a. inner membrane; b. electron transport chain 3—a. cristae (inner membrane); b. increased

surface area 4—a. matrix; b. Krebs cycle

19. NADH and FADH2 cannot be oxidized if there is no oxygen. This means that NAD+ and FAD+ are not available to reduce in the Krebs cycle if the last stage of cellular respiration does not occur. Krebs is not directly dependent on oxygen but does not occur if the dependent step (oxidative phosphorylation) is halted.

20. Dehydrogenase—It facilitates the removal of hydrogen.

21. Oxygen is the final electron acceptor. It is the most oxidative portion of the ETC. Sample analogy: When you are paid, you receive money similar to NAD receiving electrons. When you buy something, you give money to the vendor, similar to NADH giving to the ETC. The money ends up in a bank, similar to the electrons travelling to oxygen.)

22. Some protons leak through the inner membrane and do not pass through ATP synthase. Some energy is used to get pyruvate into the mitochondria. Some energy is used to transport ATP out of the mitochondria.

23. 1—activates phosphofructokinase and allows glycolysis to continue

2—citrate inhibits phosphofructokinase and stops glycolysis

3—ATP inhibits phosphofructokinase and stops glycolysis

4—NADH inhibits pyruvate dehydrogenase and prevents pyruvate oxidation

24. They contain methanogens which use electron transport chains and generate hydrogen ion gradients that provide energy for phosphorylation. They use hydrogen that is synthesized by other organisms as an energy source and carbon dioxide as an electron acceptor. The summary equation for their metabolism is:

4H2(aq) + CO2(aq) → CH4(g) + 2H2O(ℓ)

b. Climate change is caused by the buildup of methane (and other greenhouse gases) in the atmosphere, which increases the amount of radiant heat that the atmosphere traps. By capturing the methane from cows and using it for fuel, the impact would be reduced.

25. Animal muscle cells that are temporarily without oxygen carry out lactate fermentation. The pyruvate generated by glycolysis reacts with NADH to reoxidize it to NAD+. In the reaction, pyruvate is converted into lactate (also called lactic acid). The reoxidized NAD+ allows glycolysis to continue.

Chapter 4 Photosynthesis

Answers to Learning Check Questions(Student textbook page 159) 1. It represents the overall sum of many reactions. It is an

oversimplification because water and carbon dioxide don’t simply join together to make glucose.

2. Thylakoids are one of many interconnected sac-like membranous disks within the chloroplast. They contain the molecules that absorb energy from the Sun to power photosynthesis.

3. Venn diagrams should include: Light Dependent—uses light energy to make ATP and

NADPH; water is used Similarities—occur in the chloroplast Light Independent—use ATP and NADPH to

create glucose

4. Green pigments (like chlorophyll) reflect green light. The other colour wavelengths are absorbed by the plant for photosynthesis.

5. Each pigment has an ideal wavelength of light that it absorbs, meaning that a wider variety (range) of wavelengths can be absorbed.

6. Peaks represent greater light absorption. Troughs indicate that more reflection of light (less absorption) has occurred.

(Student textbook page 163) 7. To supply electrons and hydrogens for (ultimately) the

production of ATP and NADPH.

8. The movement of hydrogen ions is linked to the synthesis (creation) of ATP by chemiosmosis.

9. Venn diagrams should include: Thylakoid—found in chloroplast; contains chlorophyll

and photosystems; home of electron transport carriers that pump protons across the membrane; result in production of O2, NADPH, and ATP

Similarities— double membrane; electron transport chains; ATP synthase; increase surface area; result in the production of ATP


Cristae— found in mitochondria; home of electron transport carriers that pump protons across the membrane; result in production of ATP, NAD+, and H2O

10. Sketches should resemble Figure 4.7 on page 160 of the student textbook.

11. Non-cyclic photophosphorylation produces ATP, NADH, and oxygen gas. The electron flow is unidirectional from water to NADP+. Cyclic photophosphorylation only produces ATP. Electrons cycle and, therefore, no source of electrons (water) or sink for electrons (NAD+) is required. Excited electrons leave photosystem I and are passed to an electron acceptor. From the electron acceptor, they pass to the b6-f complex and back to photosystem I. The proton gradient is generated in the same manner as in noncyclic photophosphorylation, and ATP synthesis by chemiosmosis occurs.

12. A gradient formed with ions is more effective than one formed with neutral molecules, as both the concentration gradient and a charge gradient across the membrane contributes to the stored energy. So both a concentration gradient and voltage across the membrane build up. Both of these contribute to push a charged solute (ion) back across the membrane through the ATP synthase.

(Student textbook page 167) 13. To fix atmospheric carbon and create a three-carbon

sugar called G3P.

14. G3P

15. It is a 5C compound that CO2 immediately binds to. It is unstable and then breaks apart into two 3C compounds. This creates the cyclic nature of the Calvin cycle.

16. For every 12 G3P molecules made in the Calvin cycle, two are used to make glucose. The other 10 G3P are used to regenerate six RuBP.

17. PGA is energized by ATP through phosphorylation and reduced by NADPH to produce G3P.

18. Any three of: sucrose, starch, cellulose, RuBP

Answers to Caption QuestionsFigure 4.1 (Student textbook page 156): Examples could include other phyla of plantae such as gymnosperms, ferns, and mosses, or other protists like euglena.

Figure 4.8 (Student textbook page 161): Protons would leak across the membrane and ATP could not be produced through chemiosmosis.

Figure 4.11 (Student textbook page 166): Glycolysis

Answers to Section 4.1 Review Questions(Student textbook page 165) 1. The light-dependent reactions use light energy to

produce two high-energy compounds: ATP and NADPH. The light-independent reactions use the energy from ATP and NADPH to produce a high-energy organic molecule.

2. Sketches should resemble Figure 4.2 on page 157 of the student textbook with these parts labelled: outer membrane, inner membrane, stroma, granum, thylakoid membrane, thylakoid space.

3. An absorbance spectrum graph shows the relative amounts of different light wavelengths that a compound absorbs. The absorbance spectrum of the chlorophylls tells that chlorophyll a absorbs light wavelengths between roughly 375 and 425 nm and between 650 and 700 nm, and chlorophyll b absorbs light between 450 and 525 nm and between 635 and 660 nm.

4. A pigment is a compound that absorbs certain wavelengths of visible light. The role of pigments in photosynthesis is to absorb light energy in sunlight and pass it on to other compounds involved in the light-dependent reactions.

5. a. Diagrams should resemble Figure 4.7 on page 160 of the student textbook.

b. Circles should be around the electron and electron carrier, NADP+ + H+, NADP reductase, and NADPH. The high-energy compound formed is NADPH and it is formed by using the electron and an H+ ion to reduce NADP+ to NADPH. Students should also circle the b6-f complex and the H+ ion. The proton will help to form ATP by ATP synthase via chemiosmosis.

c. The 2H2O → 4H+ + O2 reaction should be circled. The source of the oxygen is water.

d. A hole is formed when the P680 reaction centre loses an excited electron and becomes positively charged. The source of the electrons needed to fill the hole is a water molecule. Another hole is formed when an excited electron leaves the P700 reaction centre. The electron is replaced by one from photosystem II provided by an electron carrier.

6. No, a plant could not survive solely on photosystem II because the electrons produced from photosystem I are used to reduce NADP+ to NADPH, one of the high energy molecules the plant depends on for the light-independent reactions. Without the electrons, no NADPH would be produced.


7. Venn diagram should include: Mitochondria— use chemophosphorylation; energy

provided by NADH and FADH2

Similarities—use a phosphorylation reaction to produce ATP; use ATP synthase molecule, H+ ions, and ADP to produce ATP by chemiosmosis; use electron transport systems embedded in membranes

Chloroplasts—use photophosphorylation; energy provided by light

8. If a plant contained only chlorophyll a, its ability to trap energy would be less than half the ability of a plant containing both chlorophyll a and b because it could not absorb most of the light wavelengths that chlorophyll b does.

9. The conclusion that the plant must be maximizing the use of the Sun’s energy is incorrect. If the leaves are white, then white light is being reflected. This means that little or no wavelengths are being absorbed by the leaves. It must be getting its energy from a source other than the Sun.

10. Light causes the oxidation of chlorophyll because it loses electrons through the excitation process. In oxidation reactions, electrons are lost.

11. See Figure 4.7 on page 160 of the student textbook. Circled parts should include b6-f complex, electron carrier, photosystem I, reaction centre P700, photon, 2e-, electron acceptor, 2e-, electron carrier, and the arrows that connect them.

12. Cyclic electron transport allows the plant to make additional ATP. Some anabolic reactions in plants require ATP and some require ATP and NADPH in varying amounts. By adjusting the amount of noncyclic electron transport (makes NADPH and ATP) and the amount of cyclic electron transport (makes only ATP), the photosynthetic apparatus can adjust the relative amounts of ATP and NADPH it produces to the amount needed at any particular time.

13. Analogies should show an understanding of the various parts and processes of chemiosmosis, including the proton gradient, ATP synthase, the thylakoid membrane and the production of ATP from ADP.

14. No, the splitting of water is not required for all of photosystem I’s tasks. When Photosystem I is involved in cyclic electron transport it does not need a continual supply of electrons from photosystem II as it cycles electrons and is only pumping protons across the thylakoid to make ATP. However, if NADPH is required, then photosystem II activity and water splitting is required for the continual supply of electrons needed to produce NADPH.

15. Phosphorylation is the process of attaching a phosphate to an organic compound, such as ADP. In oxidative phosphorylation, the energy needed to attach a phosphate group to ADP to form ATP comes from the flow of electrons from NADPH and FADH2 to oxygen. In photophosphorylation, the energy to create ATP comes from electrons exited by light energy. Both types of phosphorylation use chemiosmosi

Answers to Section 4.2 Review Questions(Student textbook page 171) 1. The stroma of chloroplasts 2. Carbon Dioxide Fixation Reaction|

CO2 + RUBP → unstable C6 → 2 PGA This reaction is catalysed by Rubisco 3. The overall function for the reduction phase of the

Calvin cycle is to increase the energy level of the PGA molecules by converting them into glyceraldehyde-3-phosphate, G3P.

4. Glycolysis breaks down six-carbon glucose molecules into two, three-carbon molecules producing one ATP molecule and one NADPH molecule. So, the first two steps in G3P-glucose conversion are to remove a phosphate group from ATP to form ADP and to oxidize an NADPH molecule to form NADP+.

5. Diagram should show that 10 molecules of G3P are used to create six molecules of RuBP, which is needed in phase 1 of the Calvin cycle to keep the cycle going.

6. 18 ATP, 12 NADPH 7. Of the 12 molecules of G3P produced in six turns

of the Calvin cycle, two molecules are used to make glucose or other sugars, and 10 molecules are required to replace the six molecules of RuBP, which were used in phase 1 of the Calvin cycle.

8. Photorespiration is the reaction of RuBP (ribulose-1, 5-bisphosphate) with oxygen, which essentially reverses carbon fixation. The reaction produces phosphoglycolate and 3-phosphoglycerate. The result of photorespiration is that all the energy used to regenerate RuBP is wasted, so the efficiency of photosynthesis is reduced.

9. Under hot, dry conditions, leaves lose water through the stomata (bottom arrows on left side). To reduce water loss, the stomata close as shown on the right diagram. With the stomata closed, the oxygen produced in the light-dependent reactions cannot escape and carbon dioxide cannot enter. The ratio of oxygen to carbon dioxide increases. Since oxygen and carbon dioxide compete with each other for sites on the rubisco enzyme, the amount of photorespiration increases.


10. C4 plants have a layer of cells called bundle sheath cells, which C3 plants do not have. The Calvin cycle happens only in the bundle sheath cells. In C4 mesophyll cells, carbon dioxide is fixed to a compound called PEP, producing a 4-carbon compound called oxaloacetate. Oxaloacetate is converted into malate, which is then transported into the bundle sheath cells. Once there, it is converted to pyruvate, and carbon dioxide is released into the Calvin cycle. When the climate is hot and dry, carbon dioxide levels normally decrease due to the stomata closing, and so photorespiration becomes more likely. However, the malate is pumped into the bundle sheath cells and so the carbon dioxide concentration inside the cell stays high enough for RuBP to bind with CO2 rather than oxygen. This decreases the amount of photorespiration.

11. CAM plants minimize photorespiration by separating carbon dioxide fixation from the Calvin cycle by time of day. At night, the stomata are open and carbon fixation happens, producing malate. It is then stored in a large vacuole. When the stomata are closed during the day, the carbon dioxide is removed from malate and enters the Calvin cycle.

12. CAM plants would not have an advantage over native boreal forest species. Since CAM plants are adapted to prevent photorespiration, which happens in hot, dry conditions, and the boreal forest seldom has these conditions, the CAM plants’ ability to store malate would be inefficient because it takes energy to fix carbon dioxide into malate and store it until day, when it is used in Calvin cycle.

13. The candle burned out because the combustion reaction used up all the available oxygen in the bell jar. During the 27 days, the plant photosynthesized. It used the carbon dioxide in the jar, some of which was a product of the candle’s combustion reaction, to produce glucose. The glucose was then used in cellular respiration. The by-products of cellular respiration are carbon dioxide and water. Photosynthesis must have happened at a higher rate than cellular respiration, so that oxygen unused in cellular respiration was released into the bell jar through the leaves. Enough oxygen accumulated to keep the combustion reaction going when the candle was re-lit.

14. Students will likely agree with the statement because the light-dependent reactions produce NADPH and ATP. The only source of these high-energy molecules are the light-dependent reactions. If the light-dependent reactions ceased to function, the light-independent reactions would also cease, once the NADPH and ATP were used up.

Answers to Chapter 4 Review Questions(Student textbook pages 179–80) 1. e

2. c

3. c

4. c

5. e

6. a

7. b

8. a

9. b

10. c

11. b

12. d

13. c

14. c

15. The energy levels available for its electrons will determine the wavelengths of energy (light) that a molecule can absorb.

16. Carotenoids absorb light wavelengths between roughly 450 and 525 nm. These wavelengths are not well absorbed by other pigments. So having carotenoids allows them to use more of the visible light spectrum to photosynethesize. Carotenoids are also protective; they help protect the plant from reactive oxygen species.

17. Pigments are associated with different proteins. The association with the protein fine tunes the absorbance spectrum of the pigments, some increasing the wavelength and some decreasing the wavelength. This allows clusters of pigment to trap more energy.

18. Carotenoids and other pigments in the leaves.

19. A photosystem is composed of a cluster of light-absorbing pigments in a protein-based antenna complex, and a reaction centre, which contains chlorophyll and proteins. When any pigment in a photosystem absorbs a photon, it passes the energy to the chlorophyll a molecule in the reaction centre. When it receives the energy, an electron in the reaction centre becomes excited, leaves the centre, and goes to an electron acceptor.

20. In noncyclic photophosphorylation, the P680 molecule in the reaction centre of photosystem II absorbs a photon, and an electron becomes excited and leaves the molecule. The electron moves to the primary electron acceptor. The water splitting reaction supplies another electron to the oxidized P680 so it is ready to repeat this reaction. In the meantime, an electron


carrier picks up the electron from the primary electron acceptor and gives it to the b6-f complex, which uses the electron’s energy to pump hydrogen ions into the thylakoid space. Another electron carrier then transports the electron to photosystem I, where it is re-energized by a photon. The excited electron passes to another electron acceptor, to an electron carrier, and then to NADP+ reductase, where the electron provides the energy to form NADPH.

21. One source of hydrogen ions in the thylakoid space is from water molecules, once they have been split. Hydrogen ions are also pumped from the stroma into the thylakoid space by the b6-f complex.

22. Both cyclic and non-cyclic photophosphorylation produce hydrogen ions, which create the proton gradient needed to produce ATP. However, only noncyclic photophosphorylation produces NADPH.

23. Scientists would like to mimic photosynthesis because in photosystem II, water is split to produce hydrogen and oxygen. Hydrogen is a potential source of clean fuel because it burns efficiently and does not produce carbon dioxide. However, obtaining hydrogen by other methods is difficult and often produces carbon dioxide, a greenhouse gas. If scientists could mimic the splitting of water in photosystem II, they could obtain hydrogen efficiently.

24. Stroma of chloroplasts

25. Phase 1—carbon fixation bonds atmospheric carbon dioxide to RuBP, which forms two molecules of PGA

Phase 2—reduction uses ATP and NADPH to form higher energy G3P molecules, which are used to produce glucose and other sugars

Phase 3—regeneration of RuBP; ATP is used to turn G3P into RuBP, needed for Phase 1

26. Photorespiration happens in hot dry climates because in these conditions, plants close their stomata to reduce water loss. Because carbon dioxide cannot enter the plant, the concentration of carbon dioxide decreases relative to oxygen in the mesophyll cells. Oxygen and carbon dioxide compete for sites on the enzyme rubisco. When oxygen reacts with RuBP, photorespiration occurs.

27. CAM plants increase the concentration of carbon dioxide in their chloroplasts by fixing carbon dioxide during the night when their stomata are open, forming malate. The malate is stored in a vacuole and is decarboxylated, freeing the carbon dioxide, which is fixed again to RuBP by rubisco and enters the Calvin cycle during the day, when there is enough ATP and NADPH produced to power the cycle.

28. Photorespiration consumes energy and cellular respiration produces it.

29. Because the more hydrogen ions there are in the thylakoid space, the more potential there is for the protons to help create a useable form of energy as they pass through the ATP synthase by chemiosmosis. The greater the proton gradient, the more they drive the formation of ATP, a usable form of energy for the cell.

30. The results support Mitchell’s chemiosmotic hypothesis because he artificially created a proton gradient: there was high concentration of protons inside the grana and a low proton concentration outside. Such a difference in concentrations creates the conditions needed for chemiosmosis. You would predict that there would be formation of ATP as the protons pass through the grana membranes. His experiment did produce ATP for a short time while the gradient still existed.

31. Engelman’s results show that aerobic bacteria clustered around parts of the filamentous alga that produced oxygen. Oxygen is a product of photosynthesis. Photosynthesis occurs most in the parts of the alga that were exposed to wavelengths of blue and red light. So, photosynthesis requires only certain wavelengths (blue and red which are absorbed by chlorophyll) of the visible light spectrum.

32. Chlorophyll in a leaf does not fluoresce because most of the electrons that absorb light become excited and enter the electron transport chain and their energy is used to create ATP.

33. The action spectrum shows that the plant produces the most oxygen, and therefore photosynthesizes most effectively, in the presence of wavelengths of roughly 525 nm and 575 nm. Since the absorbance spectrum shows that none of the pigments absorb effectively at those wavelengths, the diagrams show that some other pigment is involved in photosynthesis in this plant.

34. Regular fluorescent lights are not useful for growing plants indoors because they do not emit the wavelengths of light that plant pigments absorb, so photosynthesis happens poorly or not at all.

35. An uncoupler could provide a leakage path for protons through the thylakoid membrane, preventing the buildup of a proton gradient. This would not inhibit electron transport, but would stop the production of ATP. An uncoupler could also inactivate the ATP synthase enzyme in the thylakoid membrane by somehow altering its mechanism to stop it from bonding a phosphate group to an ADP molecule but still allowing the protons to pass through the ATP synthase molecule.


36. No, NADPH would be produced if chloroplasts receive only light of 700 nm or longer because photosystem I needs to replace the electron excited by a photon. Normally, it receives an electron from photosystem II. If photosystem II is inactive, it cannot provide the replacement electrons. So, no NADPH can be produced. However, cyclic electron transport could occur and ATP could be formed.

37. The electron acceptors are placed above the photosystems to indicate that the electron each acceptor receives has increased its energy content. The Y axis of the Z scheme diagrams is energy in redox potential units.

38. Sample answer: I predict that they carry out cyclic photophosphorylation because electrons have to do two things: Drive NADPH synthesis and pump protons across the membrane. If it was noncyclic, each electron would have enough energy to do only one of these things. They primarily do cyclic electron transport, but given appropriate electron donors and acceptors they can do noncyclic reactions. They are not as strongly oxidizing as PSII though, and cannot oxidize water.

39. Chloroplasts have an extensive membrane system because photosystems I and II, b6-f complex, NADP reductase, and ATP synthase are all embedded in the thylakoid membrane. The larger the membrane surface area, the more of these structures the chloroplasts can hold. Since all these structures are involved in photosynthesis, increased amounts of them mean increased amounts of photosynthesis can happen.

40. The error van Helmont made was to conclude that the mass of the tree came from water alone. He did not know about photosynthesis. The increase in mass came from one of the products of photosynthesis, which is carbohydrate, formed by water combining with carbon dioxide gas in the presence of light. At the time, it would have been difficult to imagine that all that mass came from the air.

41. The compound labelled 14C was probably PGA. It is the first stable compound in the Calvin cycle. Carbon dioxide combines with RuBP to form PGA.

42. Light energy is converted through photosynthesis to chemical energy in the leaf in the form ATP and NADPH. The energy in ATP and NADPH is used by the Calvin cycle to fix CO2 and produce glucose. Chemical energy of glucose is used to build cellulose, found in wood. The chemical energy in wood is converted to heat and light energy when it is burned in a campfire. The heat from the fire is transferred

to the marshmallow, and glucose and sucrose in the marshmallow undergo chemical changes as they cook. When the marshmallow is consumed, the chemical energy in it is released through cellular respiration, which converts the energy into ATP.

43. The concentration of RuBP would eventually decrease because normally it is constantly replenished during the Calvin cycle. Since the Calvin cycle is powered by ATP produced by the light-dependent reactions, there would eventually be no energy to run the Calvin cycle and so it would not be replenished. Similarly, PGA concentrations would eventually decrease because RuBP is converted to PGA in the cycle. So, as RuBP concentrations decrease, so would the PGA concentration.

44. Researchers might have been looking for an enzyme that would add carbon dioxide to a two-carbon compound because in Calvin’s early experiments the first products made were the three-carbon compounds PGA and G3P. Adding carbon dioxide, which has one carbon, to a two-carbon compound would produce three-carbon compounds.

45. C4 and CAM plants are less efficient in cool, moist conditions because they have adaptations to prevent photorespiration happening in their chloroplasts. Photorespiration only happens when the stomata close in hot, dry conditions to prevent water loss. Because CO2 cannot enter the leaf, oxygen levels rise relative to CO2 levels. The relative increase of oxygen means that photorespiration is more likely to occur. The adaptations to increase the levels of CO2 to prevent photorespiration in these conditions uses ATP and so costs the plant energy. But in moist, wet conditions the stomata remain open and CO2 levels remain high, so photorespiration is less likely to happen. C4 and CAM plants are using energy to prevent photorespiration that is unlikely to happen, so they are less efficient.

46. The mesophyll cells and bundle sheath cells are extremely important to C4 plants. In the mesophyll cells, carbon dioxide is fixed to PEP, eventually forming malate. The malate is transported to the adjacent bundle sheath cells, where the carbon dioxide is removed from the malate and enters the Calvin cycle. The Calvin cycle happens only in the bundle sheath cells.

47. Sketches should show low absorbance in the blue wavelengths and high absorbance in the higher wavelengths. Since the leaf is deep blue, it reflects light wavelengths that produce a deep blue colour. This leaf would then be absorbing wavelengths other than blue: the longer wavelengths green, orange, and red.


48. Sketches should resemble the chloroplast in Figure 4.2 on page 157 of the student textbook.

49. Diagrams must show that photons of light of a shorter wavelength have higher energy than photons of light of a longer wavelength.

50. An absorbance spectrum shows the relative amounts of light that a pigment absorbs at different wavelengths. An action spectrum shows the relative amounts of oxygen produced by photosynthetic organisms at different light wavelengths. These two graphs have similar shapes. So, photosynthetic oxygen production is linked to selected wavelengths of light as well as to specific pigments that absorb these wavelengths.

51. Essays should clearly describe how light energy is captured by chloroplasts converted into NADPH and ATP. It must be detailed, outline all the steps, and use all specified terms.

52. An excited electron leaving photosystem I goes to an electron acceptor and then to an electron carrier. From this carrier, it can go one of two routes. In the first route, the carrier passes the electron to the b6-f complex, and provides the complex with enough energy to pump a proton into the thylakoid space. From there, the electron returns to the P700 reaction centre in photosystem I. This is cyclic electron transport. In the second route, the excited electron goes to the same electron acceptor as the first route, but then it passes to NADP reductase and powers the reduction of NADP+ to NADPH. This is the last step in noncyclic electron transport. An excited electron cannot do both because it contains enough energy do only one of these reactions. It must be re-energized by returning to the reaction centre. Diagrams should resemble Figure 4.9 on page 162 of the student textbook.

53. 6CO2 + 18 ATP + 12 NADPH + water → 2 G3P + 16 Pi + 18 ADP + 12 NADP+

54. Rubisco accepts both oxygen and carbon dioxide. If it accepts oxygen, photorespiration happens, which reverses carbon fixation and reduces the efficiency of photosynthesis. For C4 plants, they keep carbon dioxide concentrations high by separating carbon fixation from the Calvin cycle and delivering the carbon dioxide to the Calvin cycle in a separate cell. For CAM plants, they keep the carbon dioxide concentration high by fixing carbon dioxide to form malate at night and storing it in a vacuole to be used during the day when the stomata close.

55. The components of the light-dependent reactions are embedded in the membrane because ATP synthesis occurs by chemiosmosis. For this reaction to happen, there has to be a proton gradient across a membrane. The enzymes of the light-independent reactions do not involve chemiosmosis, so they do not need to be associated with a membrane.

56. Venn diagrams should include:

C3 • CO2 fixed to form PGA

C3 and CAM • CO2 fixation and Calvin cycle happen in same cell

CAM • CO2 fixation happens at night

C4 and CAM • stomata close during the day and open at night

• CO2 fixed to form malate

C4 • Calvin cycle is in bundle sheath cell and CO2 fixation happens in mesophyll cell

C3, C4, and CAM • fix CO2 and convert it to G3P

57. energy + 6CO2 + 6H2O → glucose + 6O2Graphic organizers should show the origin of each reaction component, the role of each component in the light-dependent and/or light-independent reactions, and the relationship among the components of the reaction.

58. Graphic organizers should include the key concepts and relationships such as the locations and functions of the light-dependent reactions and light-independent reactions in photosynthesis, as well as differences in the light-independent reactions among C3, C4, and CAM plants.

59. Answers should clearly state how β-carotene is related to retinal, and show evidence of consulting at least two independent sources through documentation and critical thinking that analyses the research to reach a conclusion.

60. Essays should state an opinion supported by clearly outlined facts.

61. Sample answer: It is more beneficial to develop genetically engineered plants rather than animals because you do not have to feed plants and so the input costs might be lower. Also, you might be able to combine the production of useful compounds with food production. For example, a useful product might be produced in the leaves of corn plants, which are not edible. So, the corn plant could produce a useful product in addition to the regular corn crop.


62. Plans should show a thorough knowledge of the workings of the Z scheme and should help players remember the names of the Z scheme’s components.

63. Answers should clearly summarize the researchers’ work and show evidence of consulting at least two independent sources.

64. a. Sample answers: Increasing CO2 levels would decrease photorespiration because it would keep the CO2 level high relative to the oxygen level. Increasing the carbon dioxide levels will ultimately increase photorespiration. Or, as carbon dioxide levels increase, the climate warms, making hot dry conditions more likely. In these conditions, stomata close and internal concentrations of oxygen increase relative to CO2. So, photorespiration rates would increase.

b. Answers may or may not change, depending on answers in part a.

65. Answers should demonstrate an understanding of the chosen topic and clearly explain how it helped them understand a related concept in another area.

66. a. C4 plants are less likely to undergo photorespiration because C4 plants are able to keep the concentration of CO2 high, relative to oxygen. Oxygen competes with CO2 in the regenerating RuBP phase of the Calvin cycle. C4 plants keep the level of CO2 high, and so maintain the efficiency of photosynthesis.

b. Answers should clearly state how researchers propose to convert rice from C3 to C4 and should show evidence through documentation that at least two independent sites were consulted.

67. Each plant will produce more pharmaceutical. This increases the efficiency of production, requiring fewer plants and less agricultural space. Risks include undesirable properties and that those properties may enter the wild or unaltered population.

68. It increases the efficiency of photosynthesis by reducing the amount of photorespiration that occurs in the Calvin cycle when oxygen reacts with RuBP instead of carbon dioxide. This provides plant cells with more energy in the form of glucose. The cell can use this glucose to power many cellular processes, including growth.

69. The oxygen would have ended up in PGA molecules because CO2 enters the Calvin cycle and is added to RuBP to become PGA, which is then converted into G3P, which is the precursor of glucose and other sugars.

70. a. light-dependent reactions b. The splitting of water to extract electrons and

hydrogen ions. c. Rubisco could be linked to CO2 with the term

fixes. The Calvin cycle could be linked to the side of Carbon reactions, with the remaining terms stemming from it at an equal level: occurs in C3 plants, occurs in bundle-sheath cells of C4 plants, and occurs in the daytime in CAM plants.

Answers to Chapter 4 Self-Assessment Questions(Student textbook pages 184–5) 1. d

2. c

3. e

4. d

5. e

6. e

7. a

8. d

9. e

10. c

11. 1—stroma; 2—inner membrane; 3—outer membrane; 4—granum; 5—thylakoid space; 6—thylakoid membrane

12. The object appears black because it is absorbing all the light wavelengths that hit its surface. Because green light is shining on it, the pigments it contains absorb green wavelengths.

13. The absorbance spectrum shows the wavelengths of light photosynthetic pigments absorb and the action spectrum shows which wavelengths of light promote photosynthesis.

14. Carotenoids absorb light in the blue and green wavelengths, increasing the number of wavelengths a plant can use for photosynthesis. They also protect the plant from reactive oxygen species.

15. a. Only NADPH would be produced because, in order to produce ATP, the membrane needs to be impermeable to hydrogen ions so it can create a proton gradient that is needed for chemiosmosis to happen through ATP synthase.

b. Only ATP would be produced. The excited electrons released by photosystem II get passed to the b6-f complex, which can then pump protons across the membrane. This creates the proton gradient needed for ATP production by ATP synthase.


c. Only cyclic electron transport would occur and only ATP be produced.

16. Sketch should resemble Figure 4.8 on page 161 of the student textbook. The significance of the membrane is that it is impermeable to protons, and so creates the conditions needed to build a proton gradient across the membrane. This gradient is needed for chemiosmosis to happen through ATP synthase, which produces ATP.

17. Flow charts should show water being split into its constituent parts and show its role in role in the light-dependent reactions, donating electrons to replace the excited electron in photosystem II and its role in providing protons to the proton gradient in the thylakoid space. It should also show that the oxygen ends up in the thylakoid space but the hydrogens end up in the stroma after helping to create ATP.

18. We may be able to mimic photosystem II’s ability to split water into hydrogen and oxygen. This would be an efficient method of creating hydrogen, which could be used as a power source for fuel cells. This method would produce energy without producing carbon dioxide, so it would not release greenhouse gases.

19. During the carbon fixation phase of the Calvin cycle, atmospheric carbon dioxide is attached to RuBP to produce two molecules of a three-carbon compound, PGA.

20. The energy used in the first step is ATP. In the second step, NADPH provides the energy. NADPH is provided by the reduction of NADP+ by NADP reductase in the electron transport chain. The ATP is provided by the phosphorylation of ADP by ATP synthase in the thylakoid membrane.

21. Energy is needed to complete the conversion because the PGA molecules are more oxidized than the G3P molecules and are hence in a in a lower energy state. They are first activated by ATP and then reduced by NADPH. In their reduced state these molecules are in a higher energy state. The goal is to produce molecules that are high in energy that can be used to make glucose as an energy source for many cellular reactions.

22. six

23. 18 ATP and 12 NADPH

24. Cause and effect maps or flow charts are good choices for graphic organizers. They should show that the hot, dry weather causes the plant to close its stomata to conserve water. It should also show the relationships between the concentrations of CO and O2 and the effect this has on the reactions that take place on the rubisco enzyme as well as on the energy level.

25. a. 1—three carbons; 2—four carbons; 3—four carbons; 4—four carbons; 5—three carbons; 6—three carbons

b. 7—mesophyll cell; 8—bundle sheath cell c. Calvin cycle d. G3P, which will make glucose and other sugars e. The overall result of the C4 cycle is the concentration

of CO2 into the bundle sheath cells so that the Calvin cycle can produce high energy G3P—a starting substrate in many other metabolic pathways—without losing energy to photorespiration.

Answers to Unit 2 Review Questions(Student textbook pages 189–90) 1. b

2. a

3. c

4. d

5. c

6. b

7. d

8. b

9. d

10. b

11. b

12. a

13. b

14. c

15. a

16. • One of the three carbons in pyruvate is cleaved off (oxidized) and released as carbon dioxide.

• The remainder, called an acetyl group, becomes associated with a carrier molecule (CoA) to produce acetyl-CoA.

• This reaction is coupled to the reduction of NAD+ to produce NADH.

17. Energy enters the ETC through the reduced molecules NADH and FADH2. Their reducing power is passed on to enzymes which use this energy to pump protons into a region of high proton concentration. The energy is now associated with the concentrated protons in the intermembrane space. This energy is lost as the protons move from an area of higher concentration to an area of lower concentration through the ATP synthase enzyme channel. This enzyme uses their kinetic energy to join Pi to ADP so the energy finally rests in the new phosphate-phosphate bond of ATP.


18. Cells break down molecules to release energy that is used to make more ATP from ADP and inorganic phosphate.

19. Lactic acid fermentation can occur in muscles. In this process, enzymes break down a glucose molecule into two lactic acid molecules and transfer energy to ATP.

20. 6CO2 + 18 ATP + 12 NADPH + water → 2 G3P + 16 Pi + 18 ADP + 12 NADP+

21. Photorespiration occurs when oxygen is used as a substrate for rubisco instead of carbon dioxide. Since this produces metabolically useless products, the efficiency of photosynthesis can be reduced by up to 20 percent since production, even of waste, still requires energy.

22. Potential energy is stored for later use. In a biological system, this would be bond energy since chemical energy is stored in bonds and released when the bonds are broken. Kinetic energy is associated with movement. In this case, this means the movement associated with particles (measured as heat) and called thermal energy.

23. ATP synthase is an enzyme required for the synthesis of ATP during chemiosmosis. In mitochondria, the enzyme is embedded in the inner membrane. The hydrogen ions concentrated in the intermembrane space diffuse back across the membrane into the matrix via channels created by ATP synthase. The enzyme uses the energy of the concentration gradient to bind a phosphate group to ADP, forming ATP.

24. carbon dioxide

25. malate

26. Since the Calvin cycle takes place in the stroma, it is likely that B (the vacuole) would contain 3-carbon sugars.

27. Granum. One component is a thylakoid.

28. thylakoid membranes

29. Ethanol has been known as a clean burning fuel for hundreds of years but only recently made its way into gasoline engines. Since gasoline has always been cheaper than ethanol, it was only recently that ethanol was added to gasoline. Cars manufactured after 1980 can run on a gasohol mixture that contains up to 10 percent ethanol. To facilitate widespread ethanol use, sources must be found that do not compete with food.

30. a. pyruvate b. carbon dioxide, ATP, NADH, FADH2

c. glyceraldehydes-3-phosphate, ADP+, NADP+

31. Glucose and oxygen are two reactants of aerobic cellular respiration.

32. Phosphofructokinase is the main point of control for glycolysis. A second major point of regulation is the conversion of pyruvate to acetyl-CoA. These enzymes, as well as others in the Krebs cycles, are regulated by feedback inhibition. When molecules like ATP and NADH are in excess, they bind to allosteric sites on the enzymes, inhibiting their activities.

33. Lactic acid fermentation and alcoholic fermentation are two anaerobic processes.

34. The photosystem II centre is optimized for light at 680 nm while the photosystem I is optimized for light at 700 nm. Photosystem II obtains electrons from the splitting of water (in noncyclic photophosphorylation), and photosystem I receives electrons from electron transport originating in photosystem II. Photosystem II is used to build a proton gradient, and the major product of photosystem I is NADPH.

35. Photophosphorylation allows organisms to obtain energy from the Sun and avoid dependence on other life for energy, usually in the form of glucose.

36. During sleep, cellular respiration continues as cells function. The products of cellular respiration are carbon dioxide and water, both of which are lost through breathing. Furthermore, water mass may be lost (in varying degrees) through salivation, sweating, and evaporation.

37. The mouse (either the same one or a relative of comparable mass), the amount of sunlight and its intensity, the food source for the mouse, and the activity level and stimulation (or lack thereof).

38. a. Initially, this diet would make sense from an energy perspective since a reduction in carbohydrates would decrease caloric intake while an increase in exercise would increase caloric expenditure; both contributing to weight loss.

b. Unfortunately, metabolism primarily operates on the breakdown of sugar to provide energy for bodily function. The removal of carbohydrates from this cycle will cause energy to be taken from other sources such as protein in muscle tissue and (potentially) fat. As exercise increases, the energy demands on the body will continue protein and muscle metabolism, leading to rapid and unhealthy changes in body composition.


39. a. The pH is increasing for the first two intervals, therefore photosynthesis is using carbon dioxide and increasing the pH of the water through the removal of carbonic acid. The third interval has only a small decrease in pH, which implies that the two processes are probably occurring at the same average rate. The pH subsequently drops, indicating that carbon dioxide is being produced through cellular respiration.

b. Since there are five to nine hours of sunlight prior to a decrease in pH, t=0 is close to noon, assuming that it is the summer.

c. Since there hasn’t been an increase in pH, the Sun is likely absent, indicating a dark and cloudy day.

40. Oxidative phosphorylation couples the oxidation of NADH and FADH2 through the electron transport chain, providing energy to pump H+ across the membrane. Chemiosmosis refers to the breaking down of H+ gradient to generate ATP through ATP synthase.

41. Such a change in released energy would prompt modifications to the process of cellular respiration. The energy cycle would become an AMP-ADP process for energy transfer. In addition, because ADP is a lower-energy molecule than ATP, the cells would eventually require more available adenosine.

42. a. The intended purpose of modification would be to increase the incorporation of carbon dioxide and increase sugar production. Both of these would help the world by decreasing carbon dioxide levels and increasing food production.

b. The fact that enzymes catalyze reactions quickly and are likely limited by the amount of reactants or energy available.

43. a. A control would be the optimal operating conditions for a C3 plant. This could be determined by measuring fixation rates at various temperatures and using the highest value as the control.

b. The independent variable would be the temperature, and the dependent variable would be the amount of carbon fixed.

c. The amount of light, carbon dioxide level, water vapour level, and soil condition.

44. a. Seeds need only a small amount of water to germinate, hence the three seeds in 50 mL have far more water than required. This is a problem since heat produced will be distributed in the large volume of water, making it hard to detect. The thermometer should be suspended in the liquid to avoid measuring the heat of the table through the

flask wall. This could also be avoided if all items were at room temperature prior to starting the experiment. Furthermore, the standard classroom thermometers have an error range of 0.5°C, making small changes hard to detect.

b. Sample answer: Fill the flask with a large number of seeds and pour in room temperature water until the seeds are covered. Place a loose-fitting top on the flask, and hang an electronic thermometer (ideally with graphing capabilities) in the suspension. Insulate the entire container to retain as much heat as possible.

45. a. The individual correctly recognized that exergonic means spontaneous but, in a biological setting, spontaneous means a reaction that proceeds once enough energy is provided to make it start.

b. The demonstration could be improved by adding energy; heat, for example.

46. a. He could demonstrate that the pH of the water is increasing since photosynthesis will use carbon dioxide (dissolved in the water) and produce oxygen, which remains in the cells.

b. Since all three parts of his experiment only contain a portion of white light, each will likely be slower. Based on relative light absorption, blue would be the faster, followed by red, then green (which is would occur slowest, if at all).

c. It is possible that by selecting the first leaf-disk, the data it provides may be an outlier. It would be more accurate to select either the average time or the median time as a control value for the rate of photosynthesis.

47. Answers should include: • Glycolysis is the first set of reactions in aerobic

cellular respiration. It is an anaerobic process that takes place in the cytoplasm of the cell. During glycolysis, there is a net of two molecules of ATP in the cell and NAD+ is reduced to NADH. The fate of pyruvate, the final product of glycolysis, depends on the availability of oxygen and on the type of organism. When oxygen is available, pyruvate enters the matrix of the mitochondrion. A series of reactions yields carbon dioxide and acetyl-CoA.

• Acetyl-CoA enters the Krebs cycle by combining with a four-carbon compound. During the Krebs cycle, two carbon atoms are fully oxidized into carbon dioxide, and NAD+ and FAD are reduced to NADH and FADH2. For every molecule of acetyl-CoA, one molecule of ATP is produced.


• The reduced NADH and FADH2 that are formed during the Krebs cycle donate their electrons to the electron carriers in electron transport. As electrons are passed from one carrier to the next, the energy that is released is used to pump hydrogen ions across the mitochondrial inner membrane into the intermembrane space, creating a concentration gradient. Each NADH produced in the Krebs cycle results in three molecules of ATP, and each molecule of FADH2 produced results in two molecules of ATP.

48. Sample answer: Rubisco is the most essential enzyme for life on Earth since it catalyzes the removal of carbon dioxide from the air and incorporates this carbon into higher-energy sugar molecules, allowing non-plant life to function.

49. Diagrams should resemble Figure 4.15 on page 170 of the student textbook.

50. Sample graph:

Glycolysis

Carbon dioxide

Krebs Cycle

Pyruvate Oxidation

Free

Ene

rgy

51. a Water could be split efficiently to produce hydrogen fuel, which does not produce carbon dioxide (greenhouse gas) it burns.

b. Research should show that two independent sources were consulted.

c. Regardless of format, presentations should outline the research group’s general approach to the problem and the group’s estimate of when they hope to accomplish their goals.

52. Diagrams should be similar to the image of the mitochondrion in Figure 3.9 on page 123 of the student textbook.

53. Diagrams should indicate that lactic acid fermentation, in human cells, produces lactic acid, but alcoholic fermentation, by yeast, produces alcohol and carbon dioxide. Both processes also produce (net) two molecules of ATP.

54. The second law of thermodynamics states that energy and systems tend towards disorder. Disorder is the final state of energy in the universe. Every chemical reaction and process increases the disorder in the universe. Anabolic processes, those that build more complex systems, build up a small amount of local order while creating greater overall disorder.

55. Sample diagram:ADP

Creatine-P

ATP

Creatine

56. 1—ATP donates phosphate, making the glucose more reactive

2—metabolite is split and modified into two identical three-carbon molecules.

3—2 NAD+ are reduced 4—2 ATP are produced 5—2 water molecules are produced 6—2 pyruvate and 2 ATP molecules are generated

57. Anabolic pathways build up molecules from smaller starting materials. Photosynthesis is an example of an anabolic pathway since the larger sugar molecule is being produced. Catabolic pathways break down larger molecules either to extract energy or to obtain monomers for other anabolic reactions. Metabolic information may be used to (1) predict proper energy intake for a balanced diet and weight regulation, (2) identify problems caused by the buildup of intermediates or test for metabolites remaining after drugs have been consumed, or (3) improve sports training by understanding lactic acid formation and removal as well as the optimization of glucose metabolism (e.g., eating pasta prior to a cardiovascular activity).

58. a. Since the H+ gradient would break down ATP levels in the cell, concentrations would drop dramatically, triggering an increase in glucose oxidation. There would be a large amount of ADP present in cellular tissues, stimulating the Krebs cycle. This increase in oxidation would increase the need for oxygen and increase the amount of carbon dioxide present in the body.

b. Individuals exposed to DNF would likely have increased body temperature and increased breathing rate reflective of the increased rate of metabolism. If these are left unchecked, death may result.

59. Unreacted elements are considered to have the highest amount of energy since the process of forming bonds requires the input of energy. Therefore, ethanol has


less chemical energy than the atoms that compose it. Finally, the formation of carbon dioxide and water contain bonds that have even less energy that those in ethanol. Meaning that the combustion of ethanol will result in the released of energy.

60. a. The body normally converts phenylalanine into tyrosine. This does not occur in PKU. The additional phenylalanine builds up in neural tissues, leading to brain damage.

b. Someone with PKU must have a diet very low in phenylalanine to mitigate brain damage.

c. In Canada, children are tested for PKU at birth. Positive tests are confirmed, then parents are counselled by a nutritionist.

61. Some aerobic fitness classes offer short, vigorous workouts in which the muscle cells become depleted of oxygen. When the oxygen supply is limited, anaerobic respiration (or fermentation) occurs. It is really anaerobic respiration taking place.

62. During strenuous exercise, the amount of oxygen that can reach the muscles may be limited. As a result, anaerobic respiration (or fermentation) occurs. In anaerobic respiration, pyruvic acid is converted to lactic acid. The buildup of lactic acid in muscles causes muscle pain and fatigue.

63. Lactic acid is produced when there is insufficient oxygen to meet metabolic demands. The production of lactic acid causes a burning sensation in the muscles while its production allows for the regeneration of NAD+, giving glycolysis an electron acceptor and continuing the regeneration of ATP on a small scale. For an athlete, the burning sensation indicates that the muscle tissue is being pushed. Over time this intensity will improve the cells’ ability to tolerate and process lactic acid, increasing performance.

64. Pyruvate is transferred from the cytosol to the inner matrix of the mitochondria during cellular respiration. Extra pyruvate would be sent to the mitochondria for production of more acetyl-CoA. This could result in higher Krebs cycle activity and higher production of ATP. This may supply increased endurance. There is no justifiable explanation for the increased weight loss.

65. a. A charged battery could represent ATP and a drained battery ADP; a controlled quantity of energy is delivered, and energy delivered does useful work.

b. An active solar energy system may be represented by solar panels, wind generation, or heat pumps. In the analogy, the original source(s) of energy must be identified, transfers described, and the tasks

accomplished also described. The analogy must be reasonable. For example, the Sun is the source. The solar panel catches the light and converts it to electrical energy just like the chloroplast catches light and turns it into chemical energy. The energy transferred through wires is analogous to the ATP and NADPH produced in photosynthesis. The electrical energy from the solar panel can be used to do many mechanical tasks, just as the ATP and NADPH can be used to accomplish many metabolic tasks.

66. Answers should show an understanding of how the light-dependent and light-independent reactions are interrelated and how both these sets of reactions are related to the reactions of aerobic cellular respiration. Answers should also show the complementary nature of aerobic respiration and photosynthesis.

67. a. By increasing the production of red blood cells through the use of EPO, there would be more blood cells to absorb oxygen as the blood passed through the lungs. So, more oxygen would be available to the electron transport chain in the mitochondria, thus producing more ATP via oxidative phosphorylation.

b. Answers should clearly show how EPO is used and abused and its effects on the body. At least two independent sources must be consulted and documented. Both the intended and unintended consequences of using EPO must be shown.

68. Answers should clearly summarize the experiments Peter Mitchell did to test his chemiosmotic hypothesis and must show how these experiments supported his hypothesis. At least two independent sources must be consulted and documented.

Answers to Unit 2 Self-Assessment Questions(Student textbook pages 194–5) 1. d

2. a

3. c

4. b

5. b

6. b

7. a

8. b

9. c

10. c


11. The first law of thermodynamics states that energy cannot be created or destroyed and that the amount of energy always remains the same, although its form may vary. The second law of thermodynamics states the measure of disorder (entropy) is always increasing. These laws are significance to metabolic processes since the amount of energy that is extracted during a metabolic process will always yield less energy than is present in the food source, some energy is always “lost” to heat or other forms.

12. Chloroplasts that use cyclic photophosphorylation are able to produce more ATP than those that use noncyclic photophosphorylation. A cell would favour noncyclic photophosphorylation when doing anabolic reactions that require an electron donor, as noncyclic photophosphorylation produces NADPH that is required to reduce molecules.

13. Chemiosmosis is the process by which hydrogen ions diffuse to generate ATP through their movement from a region of higher concentration to a region of lower concentration. This process can be called phosphorylation since ADP is being phosphorylated to ATP. As the energy for this process originates from light (as collected by the photosystems) this entire process is described as photophosphorylation.

14. The oxidation of glucose is defined as a loss of electrons. Electron carriers such as NAD+ pick up these high-energy electrons and become reduced in the process. The electrons are transferred to another molecule that is subsequently reduced, eventually reducing oxygen and making water. This electron transport from NADH to oxygen is coupled to proton transport across the inner mitrochondrial membrane, leading to the development of a H+ gradient and the generation of ATP.

15. The room must be a closed system. If air can move in and out through vents, doors, and windows, the results would not be valid. Second, carbon dioxide produced by the experimenter in the room must be considered. To improve the experiment, create a small closed system with a large amount of limewater so that the solution is able to hold a large percent of the carbon dioxide that is created.

16. The Calvin cycle could be compared to someone reaching into a stream for water. Because of their juxtaposition, the individual is able to scoop with only one hand. Most of the water that is scooped is lost, but a small amount will be used. This is like the Calvin cycle since most of the energy spent in the Calvin cycle fixes carbon dioxide but very little of it actually becomes sugar. The majority of the energy is lost regenerating RuBP.

17. ATP allosterically inhibits phosphofructokinase in glycolysis, limiting this process when the cell has ample energy. Furthermore, ATP allosterically limits the activity of enzymes like α-Ketoglutarate dehydrogenase, repressing the Krebs cycle when sufficient energy is present.

18. CAM plants fix carbon dioxide at night while the stomata are open. This minimizes water loss since temperatures are low at night and less water will evaporate from the open stomata. During daytime, the stomata remain closed, preventing the escape of water and built up carbon dioxide.

19. Metabolism is the release of potential energy via the rearrangement of chemical bonds in molecules. The energy is frequently used to form new bonds as life continues. Much of the potential energy becomes kinetic energy rather than taking part in metabolism. This “loss” is essential since it provides heat for the organism, allowing enzymes to thrive under optimal working conditions.

Most reactions require an input of energy to be initiated. In cells, ATP is used to drive endergonic reactions. ATP produced from catabolic reactions is used to power anabolic reactions. This coupling of these reactions ensures that metabolism can continue.

20. a. Photosynthesis begins with the splitting of water. Researchers have recognized this as a source of hydrogen, the cleanest fuel.

b. Researchers could harness more energy here than in photosynthesis since there are fewer energy transformations required to make the final product. Each time energy is transferred, some energy is lost.

21. Methane from human waste has more potential energy since it is less oxidized.

22. Diagrams should resemble the mitochondria portion of Figure 3.9 on page 123 of the student textbook with the addition of labels for ATP production at the following pathways: glycolysis, Krebs cycle, electron transport chain, and chemiosmosis.

23. The transfer of high-energy electrons from one macromolecule to another provides energy for integral proteins to pump protons across a membrane into an enclosed region. Electrons are passed several times and protons are continually pumped until a region of higher concentration exists. Chemiosmosis occurs when hydrogen ions diffuse from an area of higher concentration to an area of lower concentration, providing energy to ATP synthase for the production of ATP.


24. a. This model works by showing how a high-energy electron releases its energy in stages, and thus becomes gradually less energized as it passes down the electron transport chain. The released energy is used to power ATP synthesis.

b. Metabolic processes such as cellular respiration require a multi-stage release of energy so that the energy of the electron is released slowly, in a manageable way. The cell has no way of harnessing the energy produced explosively when oxygen and hydrogen combine to form water. Instead, the electrons give up their energy in small amounts as they pass along the various steps of the electron transport chain.

25. The metabolic pathways involved in glucose oxidation are also involved in the metabolism of other carbohydrates, fats, and proteins.

unit 2 metabolic processes 14. - manning's · pdf filebiology 12 answer key unit 2 •...

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