Chapter 8 Practice Questions

True or False: In animal cells, most ATP synthesis takes place in the mitochondria, but in plant cells, most of the ATP used by plant cells is made in the chloroplasts.

False

True or false: The Calvin cycle is a relatively constant process, the rate of which is independent of factors such as temperature and nitrogen concentration.

False

True or False: The first photosynthetic organisms probably used chlorophyll as the primary light-absorbing pigment.

False. On page 170 of your book, it says, "Similarly, it is unlikely that these first photosynthetic organisms employed chlorophyll as a means of absorbing sunlight for the simple reason that the biosynthetic pathway for chlorophyll is complex, consisting of at least 17 enzymatic steps".

True or False: Not all photosynthetic organisms are plants, but one thing they all have in common is that they can only be found within a narrow temperature and moisture range.

False. Photosynthetic organisms can be in the photic zone which is from the surface of the ocean to about 100 meters deep because enough sunlight penetrates to enable photosynthesis. Photosynthesis can also occur in places that are moist and warm like grasslands and tropical rainforests. Photosynthesis can occur in dry regions as well with a combination of photosynthetic bacteria and unicellular algae that form an easily disturbed layer on the surface of the soil known as desert crust.

The products of the Calvin cycle are 3-carbon sugars. True or False?

True

True or False: Some of the intermediates in the biosynthesis of chlorophyll are themselves capable of absorbing light energy?

True

True or False: Collectively, most photosynthesis carried out in the ocean is performed by single-celled organisms as opposed to large, multicellular marine plants.

True.

For every six CO2 molecules incorporated into carbohydrate molecules, how many triose phosphates can be exported from the chloroplast? a. 2 b. 1 c. 10 d. 6 e. 12

a. 2 The first step of the Calvin cycle is carboxylation where carbon dioxide is combined with RuBP which produces a 6-carbon compound that immediately breaks into two molecules of 3-phosphoglycerate which is the first stable product of the Calvin cycle. Rubisco is responsible for the addition of the carbon atoms needed for the formation of carbohydrates. For energy increase to take place, carbon compounds must be reduced. NADPH (nicotinamide adenine dinucleotide phosphate) is the reducing agent that is used to transfer electrons that allow carbohydrates to be synthesized from CO2. The next step of the Calvin cycle is the reduction of the 3-phosphoglycerate that was produced when the CO2 was added to the RuBP. ATP donates a phosphate group to 3-phosphoglycerate and NADPH transfers two electrons and one proton to the phosphorylated compound which releases one phosphate group. A triose phosphate is the result of the formation of the 3-carbon carbohydrate molecule formed by the previous energy transfer. Triose phosphates are the true products of the Calvin cycle. Triose phosphates are the form that carbohydrates are exported from the chloroplast during photosynthesis.

Which of the following are produced directly as a result of the movement of electrons through a photosynthetic electron transport chain? a. ATP and NADPH b. water and carbohydrates c. oxygen and carbohydrates d. carbohydrates and ATP

a. ATP and NADPH The process of the photosynthetic electron transport chain is as follows: 1. begins with the absorption of sunlight by protein-pigment complexes 2. absorbed sunlight provides energy that drives electrons through the photosynthetic electron transport chain - movement of electrons through the transport chain is used to produce ATP and NADPH which are the energy sources needed to synthesize carbohydrates using CO2 in the calvin cycle

Assuming that all is working properly, which of the following is at a higher energy level? a. An excited-state antenna chlorophyll b. An excited-state reaction center chlorophyll

a. An excited-state antenna chlorophyll Most of the chlorophyll molecules in the thylakoid membrane act as an antennae. Energy is transferred between chlorophyll molecules until it is finally transferred to a specially configured pair of chlorophyll molecules known as the reaction center. The reaction energy is where light energy is converted into chemical energy and a result of the excited electron's transfer to an adjacent molecule. Antennae gather light energy.

What is the INITIAL carbon input in the Calvin cycle? a. CO2 b. rubisco c. triose phosphate d. C6H12O2

a. CO2 The Calvin cycle begins with carboxylation which is the addition of carbon dioxide to the five carbon structure.

A researcher is carrying out an experiment where she labels a protein with a fluorescent tag (so she can visualize its location in the cell), and introduces this tagged protein into the lumen of a single thylakoid. She observes her treated cells periodically and notices that the labled protein can move between grana, but is never observed in the stoma. What can she deduce? a. The protein likely travels through a common lumen shared by thylakoid membranes and grana, and cannot easily diffuse through the thylakoid membrane. b. This protein can easily transfer between the inner and outer mitochondria membranes. c. This protein likely travels between different thylakoid membranes by moving through the stroma, but its movement through the stroma is very brief. d. This protein cannot easily diffuse through the thylakoid membrane. e. All thylakoid membranes and grant share a common lumen, through which the labeled protein can move.

a. The protein likely travels through a common lumen shared by thylakoid membranes and grana, and cannot easily diffuse through the thylakoid membrane.

Which of the following outcomes would you expect if the pH of the thylakoid lumen increases from 4 to 6? a. The rate of ATP synthesis by ATP synthase will decrease b. The change in pH will not have a significant effect on the rate of photosynthesis c. Less oxygen will be produced d. Proton transport through ATP synthase from the thylakoid lumen to the stroma will increase. e. More NADP+ will be reduced to NADPH.

a. The rate of ATP synthesis by ATP synthase will decrease. pH is determined by the negative log of the concentration of H+ ions The more H+ ions in a solution, the more acidic it is. On page 164, it says, "When the photosynthetic electron transport chain is operating at full capacity, the concentration of protons in the lumen can be more than 1000 times greater than their concentration in the stroma (equivalent to a difference of 3 pH units). This accumulation of proteins on one side of the thylakoid membrane can then be used to power the synthesis of ATP by oxidative phosphorylation". So when the electron transport chain is working at full capacity, the liquid inside the lumen is more acidic than basic since there is a lot more of a concentration of protons in the lumen than that of the stroma. As the solution gets more basic from a transition of a pH of 4 to 6, the concentration of H+ ions in the lumen is decreasing. When there was a higher concentration of H+ ions (more acidic) it was ideal and then the synthesis of ATP was high. When there is a lesser H+ concentration, it will slow it down.

How does the metabolism occurring in chloroplasts differ from that of mitochondria? a. different electron acceptors and electron sources b. different protein sources c. different electron acceptors d. none of the other answer options is correct e. different electron sources

a. different electron acceptors and electron sources STUDY THIS

ATP production in photosynthesis requires: a. light, electrons, and protons b. electrons c. protons d. light and protons e. light

a. light, electrons, and protons Accumulation of protons in the thykaloid lumen drives the synthesis of ATP. ATP synthase synthesizes ATP in the chloroplasts/mitochondria. Cell uses light energy to produce ATP. Movement of electrons through the photosynthetic electron train leads to the formation of ATP.

Which one of the following statements BEST represents the relationship between cellular respiration and photosynthesis? a. photosynthesis stores energy in organic molecules, while respiration releases it b. photosynthesis occurs only during the day and respiration occurs only at night c. respiration occurs only in animals and photosynthesis occurs only in plants d. photosynthesis reverses the biochemical pathways of respiration e. respiration stores energy in organic molecules, while photosynthesis releases it

a. photosynthesis stores energy in organic molecule while respiration releases it

Many photosynthetic prokaryotes are capable of cyclic electron transport only. It is likely that such organisms can ____ but not ____. a. produce ATP; reduce CO2 b. reduce CO2, synthesize carbohydrates c. produce ATP, reduce H2O d. produce NADPH; oxidize H2O e. produce NADPH; reduce CO2

a. produce ATP; reduce CO2 The Calvin cycle requires two molecules of NADH and three molecules of ATP per CO2 incorporated in to carbohydrates. The transport of four electrons through the photosynthetic electron transport chain needed to reduce NADP molecules does not transfer enough protons into the lumen to produce the required 3 ATPs. In addition to the electron transport chain, another electron transport is needed to increase the production of ATP. Cyclic electron transport causes electrons from photosystem 1 to be redirected from ferrodoxin back into the electron transport chain. These electrons reenter the photosynthetic electron transfer chain.

Which of the following is an advantage of having two slightly different photosystems in the chloroplasts? a. Cells are able to use light energy at twice the maximum efficiency predicted for cells with a single photosystem. b. Electrons can be extracted from water and used to reduce NADP+ to NADPH. c. Twice as many electrons can be excited by a given amount of light energy. d. Cells are able to use both blue and green wavelengths of light for photosynthesis.

b. Electrons can be extracted from water and used to reduced NADP+ to NADPH.

During their experiments with chlorella, Calvin and Benson found no free glucose. Why do you think this is? a. Glucose would cause H2O to leave the Chlorella cells b. Glucose is stored as starch c. Glucose is an isomer of fructose d. Green algae do not respire when illuminated. e. Glucose takes too long to synthesize.

b. Glucose is stored as starch. - The Calvin cycle is capable of producing more carbohydrates than the cell needs or, in a multicellular organism, more than the cell is able to export. - If carbohydrates accumulated in the cell, they would cause water to enter the cell by osmosis which can damage the cell. Carbohydrates are formed in the reduction stage of the Calvin cycle. This can be studied on page 159 in figure 8.6. Melvin Calvin and Andrew Benson used 14CO2 to follow the incorporation of CO2 into carbohydrates. The first step in the first experiment was to inject 14CO2 into a flask containing Chlorella. (14 stands for the atomic mass, and in the 1940's radioactive 14CO2 became available in quantities that allowed experiments). The second step in the first experiment was that after a specified amount of time, drop cells of chlorella into boiling alcohol to halt the reactions. The third step in the first experiment was to identify radioactively labeled compounds using 2D paper chromatography. 2D paper chromatography separates molecules according to factors such as size and charge that affect their mobility. The results of the first experiment was that RuBP, triode phosphates, and 3-PGA all showed up. The first step of the second experiment was to shorten exposure to 14CO2 enough so that only one compound is labeled on the 2D paper chromatography. After only a short exposure to light, 3-PGA was the initial product of carboxylation. Experiment 3 was following exposure to 14CO2 as in experiment 1, it prevented carboxylation by withholding CO2 and seeing which labeled product increases and which decreases. When withholding CO2, RuBP increases while 3-PGA decreases relative to the amounts in Experiment 1, RuBP is the other substrate involved in the carboxylation step.

The terminal electron acceptor of a photosynthetic electron transport chain is: a. NADPH b. NADP+ c. oxygen d. NAD+ e. water

b. NADP+

ATP, NADPH, and NADH contain stored energy used by plant cells. Which of these molecules provides the energy that is stored in carbohydrate during the Calvin cycle? a. ATP b. NADPH c. NADH

b. NADPH Nicotinamide adenine dinucleotide phosphate is the reducing agent that is used to the Calvin cycle that transfers electrons that allow carbohydrates to be synthesized from carbon dioxide.

In the lab you isolate a chlorella mutant that is unable to switch xanthophyll pigments into the inactive, non-heat-dissipating form. if you released that mutant into a small pond shaded by trees, would the mutation spread, and why? a. Yes, because the heat released by the xanthophyll would warm up the cells and enhance photosynthesis. b. No, because mutations never spread in nature. c. No, because the light absorbed by chlorophyll would be released as heat and thus not make ATP or NADPH. d. Yes, because the xanthophylls prevent the production of reactive oxygen species. e. No, because the xanthophyll prevent the production of reactive oxygen species.

b. No, because the light absorbed by chlorophyll would be released as heat and thus not used to make ATP or NADPH. Xanthophylls slow the forming of reactive oxygen species by reducing excess light energy. They convert light energy into heat.

All cells able to carry out photosynthesis have: a. chloroplasts, mitochondria, and a plasma membrane b. a plasma membrane c. chloroplasts and mitochondria d. mitochondria e. chloroplasts

b. a plasma membrane REVIEW

The organisms believed to be the first to use two different photosystems in a single photosynthetic electron transport chain are the: a. algae b. cyanobacteria c. archaea d. green plants e. yeast

b. cyanobacteria

In the Calvin cycle, ATP is required to: a. reduce 3-PGA b. donate a phosphate group to 3-PGA c. reduce triose phosphates d. carboxylate RuBP e. reduce RuBP

b. donate a phosphate group to 3-PGA Nicotinamide adenine dinucleotide phosphate (NADPH) is the reducing agent used in the Calvin cycle and transfers the electrons that allow carbohydrates to be synthesized from CO2 so that rules out a and e. On page 158, "Regeneration of RuBP requires ATP". The reduction of 3-phosphoglyerate consists of two steps. The first step is that ATP donates a phosphate group to 3-PGA.

The fluid-filled interior compartment of the thylakoid network is referred to as the: a. stroma b. lumen c. cytoplasm d. intermembrane space e. grana

b. lumen

How many molecules of NADPH are required for 12 molecules of RuBP to be carboxylated by rubisco? a. 10 b. none of the other answer options is correct c. 12 d. 24 e. 36

b. none of the other answer options is correct the six carbon compound that is produced when carbon dioxide and RuBP immediately breaks into two molecules of 3-phosphoglycerate which is the first stable product of the calvin cycle.

Rubisco is characterized by: a. the ability to use two substrates b. slow catalysis and the ability to use two substrates c. slow catalysis d. fast catalysis

b. slow catalysis and the ability to use two substrates

Which of the following is true concerning the Calvin cycle and light harvesting reactions of photosynthesis? a. they take place in different organelles b. they take place in different compartments of the same organelle c . they take place in different types of cells in the plant d. none of the other answer options is correct

b. they take place in different compartments of the same organelle. Light dependent reactions take place in the thylakoid membrane within the chloroplast. The Calvin cycle takes place in the stroma of the chloroplast.

Which of the following is/are rubisco substrates? a. O2 b. RuBP c. CO2, O2, and RuBP d. CO2 e. CO2 and RuBP

c. CO2, O2, and RuBP Rubisco is in the carboxylation stage of the Calvin cycle and acts as a carboxylase because it adds carbon dioxide to the 5-carbon sugar called ribose 1,5-biphosphate (RuBP). Both RuBP and CO2 have to bind to the active site for the reaction to proceed. This reaction is spontaneous. According to section 8.4, rubisco can catalyze the addition of either carbon dioxide or oxygen to RuBP, but the addition of oxygen instead of carbon dioxide can substantially reduce the amount of carbohydrate produced.

Which step of the Calvin cycle would be affected first by a lack of NADPH? a. all of these choices are correct b. regeneration c. reduction d. carboxylation

c. Reduction Carboxylation is the first step within the Calvin cycle where a carbon dioxide is bonded to a 5-carbon sugar called RuPB. Reduction is the second step of the Calvin cycle where NADPH is needed. NADPH is a reducing agent that is used in the Calvin cycle that transfers electrons that allow carbohydrates to be synthesized from carbon dioxide. Reduction is the addition of an electron to something. In this step, NADPH transfers two electrons and one proton to the phosphorylated compound which releases one phosphate group to form the triose phosphates.

During photosynthesis, ____ is reduced to ___. a. water; carbon dioxide b. oxygen; water c. carbon dioxide; sugar d. carbon dioxide; oxygen e. sugar; oxygen

c. carbon dioxide; sugar

In the Calvin cycle, ATP is required to: a. reduce triode phosphates b. carboxylate RuBP c. donate a phosphate group to 3-PGA d. reduce 3-PGA e. reduce RuBP

c. donate a phosphate group to 3-PGA

In the calvin cycle, NADPH is: a. reduced b. oxidized and reduced c. oxidized d. phosphorylated e. none of the above

c. oxidized

In the evolution of photosynthesis, which process happened first? a. chloroplast membrane structure b. endosymbiosis c. the acquisition of two photosystems by cyanobacteria d. mitochondrial membrane structure

c. the acquisition of two photosystems by cyanobacteria

Light energy is converted to chemical energy in the: a. central vacuole b. nucleus c. thylakoid membrane d. cytoplasm e. mitochondria

c. thylakoid membrane The reaction center is where energy is transferred between chlorophyll molecules until it is finally transferred to a specifically configured pair of chlorophyll molecules called the reaction center In the reaction center, light is converted into chemical energy as a result. The reaction center is within the electron transport chain and the electron transport chain is within the thylakoid membrane.

In the chloroplasts of plant cells, the absorption of light energy and the movement of electrons along an electron transport chain occurs in the ___ and the synthesis of carbohydrates takes place in the ___. a. inner membrane; stroma b. inner membrane; matrix c. thylakoids; stroma d. thylakoids; matrix e. inner membrane; cytoplasm

c. thylakoids; stroma The thylakoid membranes are structures that resemble flattened sacs that are grouped into structures called grana that are within a chloroplast. Page 156 says, "The photosynthetic electron transport chain is located in the thylakoid membrane". The stroma is the region surrounding the thylakoid membrane where carbohydrate synthesis takes place. Sunlight is captured and transformed into chemical energy by the photosynthetic electron transport chain in the thylakoid membrane.

Which of the following compounds is required for the carboxylation step of the Calvin cycle? a. ATP and NADPH b. ATP c. NADPH d. RuBP e. 3-PGA

d. RuBP The carboxylation step of the Calvin cycle is where carbon dioxide is added to the five carbon molecule. Refer to page 157,158 in your book. The 5-carbon sugar is called ribulose 1,5-biphosphate (RuBP) and is catalyzed by the enzyme ribulose biphosphate carboxylase oxygenase (rubisco). RuBP and Co2 diffuse into the active site of rubisco and once the active site is occupied the addition of CO2 to RuBP proceeds spontaneously in the sense that NO ADDITION OF ENERGY IS REQUIRED. The product of caraboxylation is a 6-carbon compound that immediately breaks into two molecules of 3-phosphoglycerate (3-PGA).

Which of the following is a major evolutionary step that is hypothesized to have occurred in to evolution of photosynthesis? a. the ability to use water as an electron donor b. the acquisition by eukaryotic organisms of photosynthesis by endosymbiosis c. the acquisition by cyanobacteria of a second photosystem d. all three of these steps are hypothesized to have been important in the evolution of photosynthesis

d. all three of these steps are hypothesized to have been important in the evolution of photosynthesis

Beginning with the step catalyzed by rubisco, arrange the steps in the Calvin cycle in the proper sequence in which they occur. a. reduction, regeneration, carboxylation b. regeneration, carboxylation, reduction c. reduction, carboxylation, regeneration d. carboxylation, reduction, regeneration e. carboxylation, regeneration, reduction

d. carboxylation, reduction, regeneration

Which of the following is responsible for the transport of electrons between photosystem II and photosystem I? a. water b. chlorophyll c. NADP+ d. cytochrome b6f e. NADPH

d. cytochrome b6f

Low temperatures slow the activity of rubisco but enhance its ability to select CO2 over O2. Low temperature thus: a. increase photosynthesis rates b. increase the production of reactive oxygen species c. increase photorespiration rates d. decrease photorespiration rates

d. decrease photorespiration rates Photorespiration is the process of consumption of O2 and release of CO2 in the presence of light. The reaction speed is affected because rubisco is an enzyme that is highly selective to favor the addition of carbon dioxide over oxygen. As temperatures get lower, the activity of rubisco is slow. Rubisco wants to be slow so that it will be highly selective and choose CO2 over O2 when binding with RuBP. Rubisco can have O2, but it is bad for the cell. Photorespiration is when O2 binds to the active site, but if the reaction is slow there is a lesser chance of that happening.

Antennae accompany reaction centers, promoting ____. a. H+ transfer b. electron transfer c. heat loss d. energy transfer e. fluorescence

d. energy transfer

Where does the oxygen come from that is produced as a by-product of photosynthesis? a. from the breakdown of carbohydrates b. from the reduction of CO2 c. from the Calvin cycle d. from breakdown of water

d. from breakdown of water

Organisms with only one photosystem cannot: a. reduce CO2 b. oxidize H2S c. reduce NADP+ d. produce O2 e. reduce H2O

d. produce O2 Photosystems are protein-pigment complexes and functional and structural units that absorb light energy and use it to drive electron transport. O2 is the by-product of pulling electrons from water. Water is abundant within cells and is always available to serve as an electron donor in photosynthesis, but O2 diffuses away readily rather than accumulates. It takes a great deal of energy to pull electrons from water. The amount of energy that a single photosystem can capture from sunlight is not enough both to pull an electron from water and produce an electron donor capable of reducing NADP+. Photosystem II supplies electrons at the beginning of the electron transport chain and when Photosystem II loses an electron it is able to pull electrons from water. Photosystem I energizes electrons with a second input of light energy so they can be used to reduce NADP+.

Which of the following statements is true regarding reactive oxygen species? a. Reactive oxygen species are formed when excess electrons are added to O2. b. Reactive oxygen species are likely to form if NADP+ is rare in a cell. c. Reactive oxygen species can form when O2 is exposed to excess light energy. d. Reactive oxygen species can be neutralized by antioxidants. e. All of these choices are correct.

e. All of these choices are correct. Reactive oxygen species are highly reactive forms of oxygen that can be formed either by the transfer of absorbed light energy from antenna chlorophyll directly to O2 or by the transfer of an electron forming O2-. By the Calvin cycle's use of NADPH, NADP+ is returned to the photosynthetic electron transport chain which means any factor that causes the rate of NADPH use to fall behind the rate of light-driven electron transport can potentially lead to damage. Some chemicals can detoxify reactive oxygen species like ascorbate (vitamin C), beta carotene, and other antioxidants. Xanthophyll are yellow-orange pigments that slow the formation of reactive oxygen species by reducing excess light energy.

Which of the following statements is true regarding the Calvin cycle? a. the calvin cycle is considered a "dark" reaction because it is not directly related to photosynthesis b. the calvin cycle is a carefully regulated process because excess starch can be toxic to plant cells. c. the calvin cycle uses a rare (and thus "rate-limiting") enzyme called rubisco d. the action of rubisco is all that is necessary to produce high-energy triose phosphate from O2 e. none of the other answer options is correct.

e. None of the other answer options is correct.

From its ground state, photosystem II can: a. pull electrons from H2O b. emit light energy c. pull protons from H2O d. pass electrons to photosystem I e. absorb light energy

e. absorb light energy Photosystem II supplies electrons to the beginning of the electron transport chain. When photosystem II loses an electron and is oxidized, it is able to pull electrons from water.

Cyclic electron transport enhances ATP production because: a. cyclic electron transport is more energy efficient than linear electron transport b. proton translocation decreases c. ADP production increases d. photosystem I pumps more protons e. electrons are transferred from ferredoxin to plastoquinone

e. electrons are transferred from ferredoxin to plastoquinone

In addition to chlorophylls, light-harvesting antennae include other pigments. What is the benefit of these additional pigments? a. lower antioxidant capacity b. enhanced resonance transfer c. increased structural stability of the antenna d. tighter binding of the antennae to the thylakoid e. narrower range of wavelength reflection

e. narrower range of wavelength reflection

In a thylakoid membrane, absorbed light energy is passed from one chlorophyll molecule to another until it is: a. all of these choices are correct b. dissipated as heat c. both dissipated as heat and released as fluorescence d. released as fluorescence e. passed to a reaction center

e. passed to a reaction center