chapter 10 HW and DSM

The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce _________ to ___________.

CO2, G3P

In the light reactions, light energy is used to oxidize __________ to _______.

H2O, O2

Where does the Calvin cycle of photosynthesis occur?

Stroma

Which of the following statements correctly describes the difference in carbon fixation between C3 and C4 plants?

The first product of carbon fixation in C4 plants is a four-carbon compound instead of a three-carbon compound.

How many electrons at a time are passed between the pigment molecules in the light-harvesting complexes? a) 0 b) 1 c) 2 d) 3 e) 4

a) 0

In C3 plants the conservation of water promotes _____. a) photorespiration b) the light reactions c) photosynthesis d) a shift to C4 photosynthesis the opening of stomata

a) photorespiration

The Calvin cycle depends on inputs of chemical energy (ATP) and reductant (NADPH) from the light reactions to power the conversion of CO2 into G3P. In this exercise, consider the net conversion of 3 molecules of CO2 into 1 molecule of G3P. Drag the labels to the appropriate targets to indicate the numbers of molecules of ATP/ADP, NADPH/NADP+, and Pi (inorganic phosphate groups) that are input to or output from the Calvin cycle. Labels can be used once, more than once, or not at all.

a. 6 ATP 6 ADP b. 6 NADPH 6 NADP+ c. 6pi d. 2pi e. 3 ADP 3 ATP

Both mitochondria and chloroplasts __________.

use chemiosmosis to produce ATP

The light reactions require the cooperation of two photosystems to power linear electron flow from water to NADP+. Drag each item into the appropriate bin depending on whether the process is associated with Photosystem II (PS II) only, Photosystem I (PS I) only, or both PS II and PS I. Note that "electron transport chain" here refers to the electron transport chain between the two photosystems, not the one that functions after PS I.

-Photosystem II oxidation of water reduction of electron transport chain between the two photosystems -Photosystem I reduction of NADP+oxidation of electron transport chain between the two photosystems -Both light absorption reduction of primary electron acceptor

Redox reactions of photosynthesisIn photosynthesis, a redox compound that is produced in the light reactions is required to drive other redox reactions in the Calvin cycle, as shown in this figure along with other components of photosynthesis. Drag the terms to the appropriate blanks to complete the following sentences summarizing the redox reactions of photosynthesis. Terms may be used once, more than once, or not at all.

1. In the light reactions, light energy is used to oxidize H2O to O2. 2. The electrons derived from this oxidation reaction in the light reactions are used to reduce NADP+ to NADPH. 3. The Calvin cycle oxidizes the light-reactions product NADPH to NADP+. 4. The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce CO2 to G3P. In the light reactions, light energy is used to remove electrons from (oxidize) water, producing O2 gas. These electrons are ultimately used to reduce NADP+ to NADPH.In the Calvin cycle, NADPH is oxidized back to NADP+ (which returns to the light reactions). The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P), which then exits the Calvin cycle.

For every molecule of O2 that is released by photosystem II, _________ H2O molecules are needed, which together pass _________ electrons to the PS II reaction-center complex.

2,4

The Calvin cycle could not occur without the light reactions. Which of the following statements describes why this is the case?

ATP and NADPH produced in the light reactions provide the energy for the production of sugars in the Calvin cycle.

The light reactions of photosynthesis supply the Calvin cycle with __________.

ATP and NADPH.

Which of the following statements is a correct distinction between autotrophs and heterotrophs?

Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.

What property of the pigment chlorophyll makes it appear green?

Chlorophyll absorbs all of the visible spectrum of light except green, which it reflects.

Of the following, which occurs during the Calvin cycle?

Co2 is reduced

Which of the following processes occurs during the second phase, the reduction phase, of the Calvin cycle?

G3P production

From the following choices, identify those that are the inputs and outputs of the Calvin cycle. Drag each item to the appropriate bin. If the item is not an input to or an output from the Calvin cycle, drag it to the "not input or output" bin.

In the Calvin cycle, the energy outputs from the light reactions (ATP and NADPH) are used to power the conversion of CO2 into the sugar G3P. As ATP and NADPH are used, they produce ADP and NADP+, respectively, which are returned to the light reactions so that more ATP and NADPH can be formed.

From the following choices, identify those that are the inputs and outputs of the light reactions. (Recall that inputs to chemical reactions are modified over the course of the reaction as they are converted into products. In other words, if something is required for a reaction to occur, and it does not remain in its original form when the reaction is complete, it is an input.) Drag each item to the appropriate bin. If the item is not an input to or an output from the light reactions, drag it to the "not input or output" bin.

In the light reactions, the energy of sunlight is used to oxidize water (the electron donor) to O2 and pass these electrons to NADP+, producing NADPH. Some light energy is used to convert ADP to ATP. The NADPH and ATP produced are subsequently used to power the sugar-producing Calvin cycle.

The electrons derived from this oxidation reaction in the light reactions are used to reduce ___________ to ______________.

NADP+, NADPH

The Calvin cycle oxidizes the light-reactions product ___________ to ___________.

NADPH, NADP+

The light reactions of photosynthesis generate high-energy electrons, which end up in __________. The light reactions also produce __________ and __________.

NADPH; ATP; oxygen

In the light reactions of photosynthesis, ATP is produced by photophosphorylation. Which of the listed processes is most similar to photophosphorylation?

Oxidative phosphorylation in cellular respiration

ATP synthesis in chloroplasts is very similar to that in mitochondria: Electron transport is coupled to the formation of a proton (H+) gradient across a membrane. The energy in this proton gradient is then used to power ATP synthesis. Two types of processes that contribute to the formation of the proton gradient are: processes that release H+ from compounds that contain hydrogen, and processes that transport H+ across the thylakoid membrane. Drag the labels to the appropriate locations on the diagram of the thylakoid membrane. Note: One target of Group 1 and one target of Group 2 should be left empty.

Photosynthetic electron transport contributes to the formation of a proton (H+) gradient across the thylakoid membrane in two places. In PS II, the oxidation of water releases protons into the thylakoid space. Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space. The resulting proton gradient is used by the ATP synthase complex to convert ADP to ATP in the stroma.

Carbon dioxide and oxygen enter and exit a leaf by diffusion. Which structure(s) on a leaf allow(s) this process to happen?

Stomata

During the Calvin cycle, what happens during the carbon fixation phase?

The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.

The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why?

The Calvin cycle requires products only produced when the photosystems are illuminated.

In eukaryotes, all the reactions of photosynthesis occur in various membranes and compartments of the chloroplast. Identify the membranes or compartments of the chloroplast by dragging the blue labels to the blue targets. Then, identify where the light reactions and Calvin cycle occur by dragging the pink labels to the pink targets.

The chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions. Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.

During which process is molecular oxygen produced in photosynthesis?

The light reactions by linear electron flow

The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)

The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. A reaction or process is dependent on another if the output of the second is an input to the first. For example, the light reactions are dependent on the Calvin cycle because the NADP+ and ADP produced by the Calvin cycle are inputs to the light reactions. Thus, if the Calvin cycle slows (because of a decrease in the amount of available CO2), the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced.

Why are most autotrophs referred to as the producers of the biosphere?

They are the ultimate sources of organic compounds for all nonautotrophic organisms.

The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives this chemiosmosis is formed across which structure(s)?

Thylakoid membrane

Chlorophyll molecules are in which part of the chloroplast?

Thylakoid membranes

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

Water is oxidized and carbon dioxide is reduced.

You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?

While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.

Why is it correct to say that the linear electron flow of the light reactions directly captures energy in NADPH but only indirectly captures energy in ATP? a) Electrons are directly transferred to NADP+ to form NADPH, but electron flow is used to generate a proton gradient for ATP synthesis. Electrons are not directly transferred to ATP. b) Electrons used to generate ATP are extracted from water, but electrons used to generate NADPH come directly from PS I. c) NADPH is generated directly in the chloroplast, but ATP is synthesized in the mitochondrion. d) Light energy is used to excite electrons used to generate NADPH, but the energy used to make ATP comes from the cytochrome complex. e) Electrons are directly transferred to NADP+ to form NADPH in the electron transport chain after PS I, but ATP synthesis requires electrons that have flowed through both photosystems.

a) Electrons are directly transferred to NADP+ to form NADPH, but electron flow is used to generate a proton gradient for ATP synthesis. Electrons are not directly transferred to ATP.

Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.) a) The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. b) The rate of O2 production would remain the same because the light intensity did not change. c) The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease. d)The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle.

a) The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease.

The net reaction of the Calvin cycle is the conversion of CO2 into the three-carbon sugar G3P. Along the way, reactions rearrange carbon atoms among intermediate compounds and use the ATP and NADPH produced by the light reactions. In this exercise, you will track carbon atoms through the Calvin cycle as required for the net production of one molecule of G3P. For each intermediate compound in the Calvin cycle, identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. As an example, the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms. Labels may be used once, more than once, or not at all.

a. 3 molecules 3 carbons b. 6 molecules 18 carbons c. 6 molecules 18 carbons d. 5 molecules 15 carbons e. 3 molecules 15 carbons f. 3 molecules 15 carbons Counting carbons—keeping track of where the carbon atoms go in each reaction—is a simple way to help understand what is happening in the Calvin cycle. To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms). In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms. At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons. The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P. Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.

Which of the following is the correct order of electron flow in the light reactions of photosynthesis? a) O2 → P680 chlorophyll a pair → PS I primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS II primary electron acceptor → Fd → NADPH b) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH c) H2O → P700 chlorophyll a pair → PS I primary electron acceptor → Pc → cytochrome complex → Pq → P680 chlorophyll a pair → PS II primary electron acceptor → Fd → NADPH d) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → ATP e) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → ATP → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH

b) H2O → P680 chlorophyll a pair → PS II primary electron acceptor → Pq → cytochrome complex → Pc → P700 chlorophyll a pair → PS I primary electron acceptor → Fd → NADPH

If the Calvin cycle slows down, what will happen to the rate of O2 production in PS II, and why? a) O2 production will not change because light energy will still be absorbed by the pigment molecules and excite the PS II chlorophyll a pair. b) O2 production will slow down because less NADP+ will be regenerated in the Calvin cycle. c) O2 production will speed up because not as much NADPH will be used in the Calvin cycle and so it will accumulate in the chloroplast. d) O2 production will not change because the Calvin cycle is a separate process from the light reactions. e) O2 production will slow down because the chloroplast will need less light energy to send to the Calvin cycle.

b) O2 production will slow down because less NADP+ will be regenerated in the Calvin cycle.

When a pigment molecule in a light-harvesting complex absorbs a photon of light, what happens to its excited-state electron? a) The excited-state electron is passed to electron acceptors P680 or P700. b) The electron falls back to its ground state, while passing its excited-state energy to an electron in a nearby pigment molecule. c) The excited-state electron excites electrons in other pigments around it, so that multiple pigments can send electrons to P680 or P700. d) The excited-state electron is removed and transferred to a nearby pigment molecule, causing the next pigment to enter an excited state.

b) The electron falls back to its ground state, while passing its excited-state energy to an electron in a nearby pigment molecule.

In C4 and CAM plants carbon dioxide is fixed in the _____ of mesophyll cells. a) stomata b) stroma c) cytoplasm d) thylakoids e) grana

c) cytoplasm

The most important role of pigments in photosynthesis is to __________.

capture light energy

In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.

carbon dioxide

C4 plants differ from C3 and CAM plants in that C4 plants _____. a) are better adapted to wet conditions b) use PEP carboxylase to fix carbon dioxide c) use malic acid to transfer carbon dioxide to the Calvin cycle d) transfer fixed carbon dioxide to cells in which the Calvin cycle occurs e) open their stomata only at night

d) transfer fixed carbon dioxide to cells in which the Calvin cycle occurs

The energy used to produce ATP in the light reactions of photosynthesis comes from __________.

movement of H+ through a membrane

When chloroplast pigments absorb light, __________.

their electrons become excited

How does carbon dioxide enter the leaf?

through the stomata

The light reactions of photosynthesis occur in the __________.

thylakoids

The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from

water

Where do the electrons entering photosystem II come from?

water